Active damping control for an underactuated multibody system

Light-weight robots and manipulators stand out due to their very good weight-to-load ratio and a low energy consumption. Unfortunately, the light-weight design yields a lower stiffness, which results in undesired elastic deformations, especially during high-speed working motion. One way to limit these unwanted oscillations can be implemented with modifications of the command signals, e.g. by input shaping or pre-computed feed-forward control. However, a feedback control-concept has the ability to provide a fast compensation of elastic deformations due to high-speed working motions or in case of unwanted environment contact as well as in the presence of other external disturbances. In this contribution, an active damping control (ADC) for fast moving manipulators with significant structural elasticities is presented. This approach does not require additional actuators and it is suitable for a large variety of manipulators that exhibit structural vibrations. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Stereoselective self-sorting in the self-assembly of a Phe-Phe extended guanidiniocarbonyl pyrrole carboxylate zwitterion: formation of two diastereomeric dimers with significantly different stabilities

The 'dipeptide extended' guanidiniocarbonyl pyrrole carboxylate zwitterion GCP-Phe-Phe 1 forms stable dimers in DMSO. However, dimerization is highly stereoselective. Only homochiral dimers are formed and the (L,L)·(L,L) dimer (K(dim) > 10(5) M(-1)) is significantly more stable by a factor of 10(3) than the diastereomeric (D,L)·(D,L) dimer (K(dim) = 120 M(-1)).     

A Supramolecular Stabilizer of the 14‐3‐3ζ/ERα Protein‐Protein Interaction with a Synergistic Mode of Action

We report on a stabilizer of the interaction between 14‐3‐3ζ and the Estrogen Receptor alpha (ERα). ERα is a driver in the majority of breast cancers and 14‐3‐3 proteins are negative regulators of this nuclear receptor, making the stabilization of this protein‐protein interaction (PPI) an interesting strategy. The stabilizer ( 1 ) consists of three symmetric peptidic arms containing an arginine mimetic, previously described as the GCP motif. 1 stabilizes the 14‐3‐3ζ/ERα interaction synergistically with the natural product Fusicoccin‐A and was thus hypothesized to bind to a different site. This is supported by computational analysis of 1 binding to the binary complex of 14‐3‐3 and an ERα‐derived phosphopeptide. Furthermore, 1 shows selectivity towards 14‐3‐3ζ/ERα interaction over other 14‐3‐3 client‐derived phosphomotifs. These data provide a solid support of a new binding mode for a supramolecular 14‐3‐3ζ/ERα PPI stabilizer.     

Hydroformylation of alkenes with paraformaldehyde catalyzed by rhodium-phosphine complexes

The hydroformylation of medium-chain C6 olefins and of allyl alcohol was achieved with paraformaldehyde in dioxane solution using rhodium catalysts with mono-, bi-, and tri-dentate phosphine ligands. The highest activities with n/i ratios around 2, were obtained for a system derived from [Rh(dppe)₂]⁺, prepared in situ by reaction of Rh(acac)(CO)₂ with 2 eq of dppe.     

Characterization of Photodegradation of Meta-tetra (Hydroxyphenyl)chlorin (mTHPC) in Solution: Biological Consequences in Human Tumor Cells

The photobleaching of meta -tetra(hydroxyphenyl)chlorin m THPC) (irradiation wavelength 413 nm) in protein-containing solution was evaluated by decay in absorbance in Soret band and in fluorescence (λ_exc= 423 nm, λ_em= 655 nm). Light exposure resulted in a decrease in absorption throughout the spectrum and simultaneous appearance of new absorption bands in the spectral region 325–450 nm. The rate of m THPC photodegradation, followed by decay in absorbance, was 15-fold lower than that observed in fluorescence. This fact reflects the photobleaching of presumably monomeric, fluorescing species of m THPC. In order to determine the consequences of photobleaching of fluorescing m THPC material on cellular uptake and photocytotoxicity, human HT29 colon adenocarcinoma cells were incubated with photobleached m THPC during 5 h with or without following irradiation with the fixed fluence. Surprisingly, but up to the time when the fluorescence decreased by 50%, only a slight decrease in photocytotoxicity was detected. Either aggregated forms that have been taken up undergo intracellular monomerization (but we did not observe increase in fluorescence in living cells) or the photodynamic activity is mostly due to aggregates. The discrepancy of m -THPC-photodynamic therapy (PDT) effect and fluorescence measurements may suggest that aggregated m -THPC plays an important role in m THPC-PDT.     

Screening of a combinatorial library reveals peptide-based catalysts for phosphorester cleavage in water

A combinatorial library of 625 octapeptides was screened for their efficiency to catalyze phosphorester cleavage in water. Octapeptides such as 1c, which contains a catalytically active histidine and two cationic residues (Gua) as potential anion-binding sites, show substrate hydrolysis in water. Metal-free catalysis with a rate enhancement of up to a factor of 175 over the uncatalyzed background reaction is observed.     

Artificial ditopic Arg-Gly-Asp (RGD) receptors

Covalent fusion of two artificial recognition motifs for arginine and aspartate resulted in a new class of ditopic RGD receptor molecules, 1-4. The two binding sites for the oppositely charged amino acid residues are linked by either flexible linkers of different length (in 1-3) or a rigid aromatic spacer (in 4). These spacers are shown to be critical for the complexation efficiency of the artificial hosts. If the linkers are too flexible, as in 1-3, an undesired intramolecular self-association occurs within the host and competes with, and thereby weakens, substrate binding. The rigid aromatic linker in 4 prevents any intramolecular self-association and hence efficient RGD binding is observed, even in buffered water (association constant of K(a) approximately 3000 m(-1)). A further increase in hydrophobic contacts, as in host 16, can complement the specific Coulomb attractions, thereby leading to an even more stable complex (Ka=5000 m(-1)). The recognition events have been studied with NMR spectroscopy, UV/Vis spectroscopy, and fluorescence titrations.     

A Tailor‐Made Specific Anion‐Binding Motif in the Side Chain Transforms a Tetrapeptide into an Efficient Vector for Gene Delivery

Arginine‐rich cell‐penetrating peptides are widely utilized as vectors for gene delivery. However, their transfection efficacy still needs to be optimized. To accomplish this, guanidinocarbonylpyrrole groups, which are tailor‐made anion binding sites, were introduced into the side chains of tetralysine to obtain the peptide analogue 1 . In contrast to the common strategy of adding a lipophilic tail to peptide vectors, this novel method most likely enhances transfection efficacy through more specific interactions between the binding motifs and DNA or the cell membrane. Tetrapeptide analogue 1 is thus the smallest peptidic transfection vector that has been reported to date. The transfection efficacy of 1 , which on average has less than two positive charges under physiological conditions, is even better than that of polyethylenimine (PEI). Furthermore, 1 exhibits only negligible cytotoxicity, which makes it an interesting candidate for further development.     

Gerrymander-proof representative democracies

International Journal of Game Theory - This article is devoted to the analysis of electoral systems involving two step procedures. It appears that designers are able to manipulate the result of...