Variational multirate integration in multi-body dynamics

For systems that contain slow and fast dynamics, variational multirate integration schemes are used. These schemes split the system into parts which are simulated using two time grids consisting of micro and macro nodes. This formulation can be extended for multi-body systems. The rigid multi-body system is described by the so called director formulation and constraints describing the joints connecting the bodies. With the Lagrange multiplier method, the constraints are introduced into the equations of motion. A way to implement the null space method into the variational multirate framework is shown and the influence on the number of unknowns is investigated. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Effects of Embedded Dipoles in Aromatic Self‐Assembled Monolayers

Using a representative model system, here electronic and structural properties of aromatic self‐assembled monolayers (SAMs) are described that contain an embedded, dipolar group. As polar unit, pyrimidine is used, with its orientation in the molecular backbone and, consequently, the direction of the embedded dipole moment being varied. The electronic and structural properties of these embedded‐dipole SAMs are thoroughly analyzed using a number of complementary characterization techniques combined with quantum‐mechanical modeling. It is shown that such mid‐chain‐substituted monolayers are highly interesting from both fundamental and application viewpoints, as the dipolar groups are found to induce a potential discontinuity inside the monolayer, electrostatically shifting the core‐level energies in the regions above and below the dipoles relative to one another. These SAMs also allow for tuning the substrate work function in a controlled manner independent of the docking chemistry and, most importantly, without modifying the SAM‐ambient interface.     

Rational Design of Macromolecular Structures: Focusing on the Embryonic Stages of Polymerization

Acetate-terminated oligomers of fluoral, chloral and bromal, prepared with the lithium alkoxides of tert-butanol and (-)-borneol, were analyzed by gas chromatography, polarimetry, NMR and mass spectroscopies, and by single crystal x-ray diffraction methods. The configurational and conformational properties of the “embryonic” adducts were found to depend strongly on the relative size of the trihalomethyl side group in these systems. The results of our efforts, summarized here, help to shed new light on the origins of helical geometry and crystalline order in polymers of the perhaloacetaldehydes.     

Functional Polymers. X. Hydrolysis Studies of Polyesters and Polycarbonates of Bithionol and Their Copolymers

The hydrolysis behavior of a number of polymers of bithionol [2,2′-thiobis(4,6-dichlorphenol)] was investigated. The hydrolysis of polyesters of bithionol with aliphatic or aromatic dicarboxylic acids or phosphorus acids as well as polycarbonates and alternating copolycarbonates and polyurethanes or co(po1y-carbonates/polyurethanes) depends primarily on the water solubility of the polymer or at least on its degree of swelling. In the most favorable case of the alternating bithionol/PEG 4000 co-polycarbonate the hydrolysis rate of the polymer at 37°C was 1.62 L/mol/min at pH 10, 0.63 L/mol/min at pH 4 and 0.17 L/mol/min at pH 7.4. Copolycarbonates and copolyurethanes with PEG 4000 in the polymer chain have slightly lower rates of hydrolysis. When the solubility of the polymer is low and the crystallinity     

Functional Polymers. VIII. Polyesters from Hindered Bisphenols

It was demonstrated that highly hindered bisphenols could be used to produce polyesters of moderate molecular weight. Bisphenols linked in the 4 and 4′ or the 2 and 2′ positions and substituted in positions ortho and para to the phenolic hydroxyl groups with methyl or tertiary butyl groups (these bisphenols are now used as very effective antioxidants) formed polymers, their reactivity depending more on the nature of the group linking the two phenyl rings than on the steric effects of the ortho substi-tuents. Bisphenols linked in the 2 and 2′ positions and containing bulky electron-withdrawing groups were found to be least effective as condensation monomers although successful polymerization to moderate molecular weight could be achieved using me it polycondensation techniques.     

Oriental Lacquer. 10. The South East Asian Lacquer

Abstract

The family Anacardiaceae consists of 76 genera and about 600 species. A comparison of the species of Anacardiaceae is discussed with special emphasis on the importance of the exudates, the so-called sap, for their importance as lacquer to produce lacquer ware. Many exudates are poisonous. The individual chemical compounds which constitute the active ingredients of the oleoresin part of the sap and their function are described based on space-filling molecular models. Emphasis is also given to the organic components of lacquer trees of the South East Asian region, which is compared to other species of the Anacardiaceae family.     

Preparation and Characterization of Head-to-Head Polymers. III. Head-to-Head Poly (methyl Crotonate)

Alternating copolymers of cis-butene-2 and maleic anhydride were esterfied to the methylester which corresponds to head to head (H-H) poly(methyl crotonate).

The chemical, physical, and mechanical properties and thermal degradation behavior of H-H poly (methyl crotonate) was studied and compared with the properties of head to tail (H-T) poly(methyl crotonate). This latter polymer was made by a known anionic polymerization technique and was, unlike the amorphous H-H polymer, partially crystalline. The T_g of H-H polymer was found to be higher than that of the H-T polymer. Thermal degradation behavior of H-H and H-T polymer was between the degradation behavior of H-H and H-T poly(methyl cinnamate) and poly (methyl acrylate). Poly (methyl crotonates) degraded to a substantial part to small molecules and char; methyl crotonate was found among the degradation products. H-H Poly (methyl crotonate) gave also butene-2 and a mixture of dimethyl maleate and dimethyl fumarate on pyrolysis.     

The need for new isotope reference materials

Isotope reference materials are needed to calibrate and validate analytical procedures used for the determination of isotope amount ratios, procedurally defined isotope ratios or so-called δ values. In contrast to the huge analytical progress in isotope ratio analytics, the production of isotope reference materials has not kept pace with the increasing needs of isotope analysts. Three representative isotope systems are used to explain the technical and non-technical difficulties and drawbacks, on one hand, and to demonstrate what can be achieved at its best, on the other hand. A clear statement is given that new isotope reference materials are needed to obtain traceable and thus comparable data, which is essential for all kinds of isotope research. The range of available isotope reference materials and δ reference materials should be increased and matrix reference materials certified for isotope compositions or δ values, which do not exist yet, should be provided.     

Comparison of copper labeling followed by liquid chromatography-inductively coupled plasma mass spectrometry and immunochemical assays for serum hepcidin-25 determination

Hepcidin-25 has been defined as the key biomarker in iron metabolism. This peptide binds to the iron transporter ferroportin to cause its degradation. Therefore, the need for specific, accurate and precise methods for the quantification of hepcidin-25 in biological fluids is dramatically increasing. In this regard, the use of rapid immunochemical methods that provide low limit of quantification is desired for routine clinical use. However, such fast methodologies should be first analytically evaluated and compared with alternative strategies to check for their advantages and limitations. Here we compare the use of a commercial immunochemical assay for hepcidin determination with a novel analytical approach based on Cu-labeling of the peptide followed by Cu determination using liquid chromatography (HPLC) and plasma mass spectrometry (ICP-MS). The figures of merit of both systems reveal similar analytical characteristics and both seem to be adequate for the determination of the peptide at biologically relevant concentrations in human serum samples. The analysis of a larger number of samples (n = 50) by both techniques showed a good agreement in the concentrations found. Such finding permits to address the hepcidin recovery in the sample preparation procedure necessary for the HPLC-ICP-MS analysis in human serum that turn out to be 76–85%. Additionally, limitations due to cross-reactivity issues of the ELISA method could be addressed in some of the samples by using LC-ICP-MS and were confirmed by LC-Electrospray-MS.