Catalysis of cationic surfactants in organic solvent: Hydrolysis of 2-nitro-4-carboxyphenyl acetate

Journal of Inclusion Phenomena and Macrocyclic Chemistry - The hydrolysis reaction of 2-nitro-4-carboxyphenyl acetate was studied in dichloromethane in the presence of an added electrolyte (NaOH)...     

E stereoregular 1,1 and 1,3 constitutional units from 1,3-butadiene in copolymerizations catalyzed by a highly hindered c(2) symmetric metallocene

Unprecedented 1,1 and 1,3 constitutional units from 1,3-butadiene, both presenting only the E configuration of the double bond, have been achieved by copolymerization with ethene, conducted at high temperature and low ethene concentration, when catalyzed by a highly hindered C(2) symmetric metallocene. Ethene/butadiene copolymerizations by this catalyst generally lead to prevailing methylene-1,2-cyclopropane units from butadiene. Polymer microstructures obtained for different comonomer concentrations clearly indicate that the rate-determining step leading to cyclopropanation involves ethene, while that leading to 1,1 and 1,3 constitutional units does not. A general copolymerization scheme and a molecular modeling study of the cyclopropanation reaction are presented. Molecular modeling also indicates that the E stereoselectivity for 1,1 and 1,3 constitutional units can be rationalized, in the assumption that an allyl isomerization of the terminal of the growing chain would occur.     

A combinatorial characterization of quadrics

In this paper we prove that in a projective space of dimension three and orderq the two plane characterk-sets fork {q ²+ 1,(q+1)²} are of the same type as the elliptic or the hyperbolic quadric, respectively. As a corollary we obtain a characterization of the elliptic and the hyperbolic quadrics.     

Complex Dirichlet Forms: Non Symmetric Diffusion Processes and Schrödinger Operators

The concept of complex Dirichlet forms ^c resp. operators L _c in complex weighted L ²-spaces is introduced. Perturbations of classical Dirichlet forms by forms associated with complex first-order differential operators provide examples of complex Dirichlet forms.Complex Dirichlet operators L _c are unitarily equivalent with (a family of) Schrödinger operators with electromagnetic potentials.To ^c there is associated a pair of real-valued non symmetric Dirichlet forms on the corresponding real weighted L ²-spaces, which in turn are associated with (non-symmetric) diffusion processes.Results by Stannat on non symmetric Dirichlet forms and their perturbations can be used for discussing the essential self-adjointness of L _c .New closability criteria for (perturbation of) non symmetric Dirichlet forms are obtained.     

Oxidation of aqueous solutions of cobalt(II) in the presence of some aminoacids

Summary The complexes between cobalt(III) and aminoacids such as glutamine, asparagine, glutamic acid, aspartic acid and proline were studied.Cobalt(III)-aminoacid systems were investigated by spectrophotometry after oxidizing the cobalt(II) complexes by sodium peroxide. The variation of the absorption spectra shows the pH dependence of the process and it is clear that the formation of the complexes occurs through oxo-intermediates.Complexation ratios, molar absorptivity values and the concentration quotients at equilibrium were determined at pH 2.2 to avoid the formation of binuclear dioxygen-cobalt complexes.     

Enantioselective synthesis of DIANANE, a novel C2-symmetric chiral diamine for asymmetric catalysis

DIANANE (endo,endo-2,5-diaminonorbornane) is a novel chiral C(2)-symmetric diamine, based on the rigid bicyclo[2.2.1]heptane scaffold. Schiff-base ligands derived from DIANANE have already found use in asymmetric catalysis, e.g., in the highly enantioselective Nozaki-Hiyama-Kishi reaction. We herein describe a practical synthesis of enantiomerically pure DIANANE, starting from norbornadiene in four steps: (i) Pd-MOP catalyzed Hayashi-hydrosilylation/Tamao-Fleming oxidation, (ii) oxidation to norbornane-2,5-dione, (iii) endo-selective reductive amination with benzylamine, and (iv) hydrogenolytic debenzylation. None of the steps involves chromatographic purification. For the Tamao-Fleming oxidation, the use of hydrogen peroxide in the form of its urea clathrate instead of aqueous solution proved beneficial. By the above sequence, enantiomerically pure (ee >or=99%) DIANANE was obtained from norbornadiene in 40-50% overall yield. The relative and absolute configuration of DIANANE was confirmed by X-ray crystallography of the DIANANE bis-tosylamide, and of its bis-camphorsulfonamide. Furthermore, the synthesis and X-ray crystal structure of the Schiff-base ligand derived from DIANANE and 3,5-di-tert-butyl salicylic aldehyde are reported.     

Diastereoselective aziridination of chiral alpha-carbonyl enoates

Nosyloxycarbamates very efficiently aziridinate optically active alpha-carbonyl enoates with high levels of diastereoselectivity under mild conditions and in a straightforward process.     

Synthesis of Chiral MOF-74 Frameworks by Post-Synthetic Modification by Using an Amino Acid

The synthesis of chiral metal–organic frameworks (MOFs) is highly relevant for asymmetric heterogenous catalysis, yet very challenging. Chiral MOFs with MOF-74 topology were synthesised by using post-synthetic modification with proline. Vibrational circular dichroism studies demonstrate that proline is the source of chirality. The solvents used in the synthesis play a key role in tuning the loading of proline and its interaction with the MOF-74 framework. In N,N′-dimethylformamide, proline coordinates monodentate to the Zn²⁺ ions within the MOF-74 framework, whereas it is only weakly bound to the framework when using methanol as solvent. Introducing chirality within the MOF-74 framework also leads to the formation of defects, with both the organic linker and metal ions missing from the framework. The formation of defects combined with the coordination of DMF and proline within the framework leads to a pore blocking effect. This is confirmed by adsorption studies and testing of the chiral MOFs in the asymmetric aldol reaction between acetone and para-nitrobenzaldehyde.     

Effect of thermal treatment under high pressure on the quality of a meat sauce

Abstract

It is known that pressure alone is not able to make shelf-stable any food stored in room conditions. Acid products are normally spoiled by enzymes, and low acid products are spoiled even by spore-forming micro-organisms. To overcome the problem the role of heat in the process has been re-evaluated and the possibility of destroying at the same time spores and enzymes has been found. This work compares the effect of sterilisation by High Pressure Processing (HPP) with one of the conventional retort processing techniques. Two batches of meat sauce were kept in room conditions over a year and their quality was evaluated periodically during the shelf life simulation. The physico-chemical characteristics of the retorted ones showed a progressive appearance of the typical thermal damage. The High Pressure Sterilised samples on the contrary showed limited damage, related to the unavoidable pre-heating. Their quality markers were constant over the shelf life evaluated period.