Continuous stochastic detection of amino Acid enantiomers with a protein nanopore

A stochastic sensing method: Discrimination between enantiomeric amino acids is achieved when the amino acids bind to a Cu(II) complex within a protein nanopore sensor, which provides a chiral environment. The potential of the method is demonstrated by real-time observation of the increase in enantiomeric excess during an enzymatic kinetic resolution.     

Predicting the efficiency of antioxidants in polymers

The efficiency of antioxidants in polymers is determined by three processes: the chemical reactivity, the physical loss and a minimal effective concentration. In most cases, loss of the stabiliser by physical processes (evaporation, leaching) is more significant than the loss by chemical consumption. In this paper, a model is proposed that relates the protection time of an antioxidant to the migration in a polymer matrix. The parameters that determine the migration, i.e. mobility (D) and solubility (S) are predicted using theoretical modelling. A linear correlation was found between the protection time and the function −S ln(D). In some cases this correlation is better than that of the empirical model proposed by Moisan, ln(S²/D).     

Large Eddy Simulation of the sound field of a round turbulent jet

In this paper we will use Large Eddy Simulation (LES) to obtain the flow field of a turbulent round jet at a Reynolds number based on the jet orifice velocity of 11000. In the simulations it is assumed that the flow field is incompressible. The acoustic field of the jet is calculated with help of the Lighthill acoustic analogy. The coupling between the flow solver and the acoustic solver is discussed in detail. The Mach number used in the acoustic calculation was equal to 0.6. It is shown that the decay of the jet centerline velocity and centerline rms are in good agreement with experimental data of [12]. Furthermore, it is shown that the influence of the LES modeling on the acoustic field is very small, if the dynamic subgrid model is used.     

Highly enantioselective DNA-based catalysis

A new approach to DNA-based asymmetric catalysis is presented, which gives rise to very high enantioselectivities (up to 99% ee) in the copper catalyzed Diels-Alder reaction in water.     

A Kinetic and Structural Investigation of DNA‐Based Asymmetric Catalysis Using First‐Generation Ligands

The recently developed concept of DNA‐based asymmetric catalysis involves the transfer of chirality from the DNA double helix in reactions using a noncovalently bound catalyst. To date, two generations of DNA‐based catalysts have been reported that differ in the design of the ligand for the metal. Herein we present a study of the first generation of DNA‐based catalysts, which contain ligands comprising a metal‐binding domain linked through a spacer to a 9‐aminoacridine moiety. Particular emphasis has been placed on determining the effect of DNA on the structure of the Cu^II complex and the catalyzed Diels–Alder reaction. The most important findings are that the role of DNA is limited to being a chiral scaffold; no rate acceleration was observed in the presence of DNA. Furthermore, the optimal DNA sequence for obtaining high enantioselectivities proved to contain alternating GC nucleotides. Finally, DNA has been shown to interact with the Cu^II complex to give a chiral structure. Comparison with the second generation of DNA‐based catalysts, which bear bipyridine‐type ligands, revealed marked differences, which are believed to be related to the DNA microenvironment in which the catalyst resides and where the reaction takes place.     

Homogeneous vanadium-based catalysts for the Ziegler-Natta polymerization of alpha-olefins

Although their activity is often inferior to that of other systems, the use of vanadium-based catalysts in homogeneous Ziegler-Natta polymerizations allows the preparation of high-molecular-weight polymers with narrow molecular-weight distributions, ethene/alpha-olefin copolymers with high alpha-olefin incorporation, and syndiotactic polypropene. The main reason for the low activity of these catalysts is their deactivation during catalysis by reduction of active vanadium species to low-valent, less active or inactive species. We here present an up-to-date review of this area with particular emphasis on the attempts to improve catalyst performance and stability by the use of additives or ancillary ligands.     

Antibodies to short synthetic peptides for specific recognition of partly denatured protein

On immunization with subclasses of homologous proteins, the presence of immunodominant class-specific structures often prevents the development of subclass specific antibodies. Immunization with synthetic peptides representing specific structures in such a protein can then be used instead. Sequences derived from human IgG2 and Staphylococcus aureus enterotoxin were used as a model to develop general criteria for immunization with synthetic peptides. Peptide sequences were selected on the basis of criteria such as hydrophilic property, surface probability and secondary structure, which together constitute an antigenic index. The carrier proteins keyhole limpet hemocyanin and chicken gammaglobulin were coupled by using either carbodiimide or a maleimide. Peptide-specific responses can be elicited regardless of the sequence. Some coupling conditions influenced the specificity of the antibody responses. The results of immunization with short peptides not representing a natural B-cell determinant of a protein suggest that the frequency of native protein-recognizing antibodies is considerably lower than that of antibodies that recognize the protein in a partly denatured or altered state.