A design of experiments concept for the minimization of nonspecific peptide adsorption in the mass spectrometric determination of substance P and related hemokinin‐1

Substance P and hemokinin‐1 were predominantly examined by immunoassays with their limitation to differentiate appropriately between both peptides. The use of liquid chromatography coupled with tandem mass spectrometry is a promising, highly selective alternative. Adsorption processes have been identified in preliminary experiments to play a crucial role in the loss of mass spectrometry intensity of both peptides. Therefore, a design of experiments concept was created to minimize nonspecific peptide adsorption. For this purpose, the most critical influencing parameters—(1) the composition of the injection solvent as well as (2) the most suitable container material—were systematically and concordantly investigated. The addition of modifiers, such as formic acid, dimethyl sulfoxide, and organic solvents, to the injection solvent led to a substantial gain of intensity of substance P and hemokinin‐1 compared to the start gradient as an injection solvent. Furthermore, the systematic investigation underlined the high impact of the container material, demonstrating polypropylene as the most favorable material. A conjoint injection solvent optimum was found to determine both peptides simultaneously by the conduction of a sweet‐spot analysis. The experimental design substantially reduced nonspecific peptide adsorption and enabled the simultaneous and selective determination of endogenous substance P and hemokinin‐1 plasma levels.     

Shape-Aware Matching of Implicit Surfaces Based on Thin Shell Energies

A shape sensitive, variational approach for the matching of surfaces considered as thin elastic shells is investigated. The elasticity functional to be minimized takes into account two different types of nonlinear energies: a membrane energy measuring the rate of tangential distortion when deforming the reference shell into the template shell, and a bending energy measuring the bending under the deformation in terms of the change of the shape operators from the undeformed into the deformed configuration. The variational method applies to surfaces described as level sets. It is mathematically well-posed, and an existence proof of an optimal matching deformation is given. The variational model is implemented using a finite element discretization combined with a narrow band approach on an efficient hierarchical grid structure. For the optimization, a regularized nonlinear conjugate gradient scheme and a cascadic multilevel strategy are used. The features of the proposed approach are studied for synthetic test cases and a collection of geometry processing examples.     

Influence of the aluminum alkyl co-catalyst type in Ziegler-Natta ethene polymerization on the formation of active sites, polymerization rate, and molecular weight

The influence of the concentration of the co-catalysts triethylaluminium (TEAL), tri-iso-butylaluminium (TIBAL), tri-n-octylaluminium on the polymerization rate for standard Ziegler-Natta catalyst systems was studied. By comparing the influence of monomeric TIBAL with TEAL co-catalyst on the polymerization activity, the effect of TEAL dimerization was described. The use of the Eley-Ridealadsorption model instead of Langmuir-Hinselwood model is proposed for the absorption of monomeric aluminiumalkyl species and for the formation of active centers C*. It is further proposed that steric hindrance from different co-catalysts, which results in a higher molecular weight (MW) of polymers, is caused by active centers with reduced space for chain transfer reactions.