Biocatalytic Feedback‐Driven Temporal Programming of Self‐Regulating Peptide Hydrogels

Switchable self‐assemblies respond to external stimuli with a transition between near‐equilibrium states. Although being a key to present‐day advanced materials, these systems respond rather passively, and do not display autonomous dynamics. For autonomous behavior, approaches must be found to orchestrate the time domain of self‐assemblies, which would lead to new generations of dynamic and self‐regulating materials. Herein, we demonstrate catalytic control of the time domain of pH‐responsive peptide hydrogelators in a closed system. We program transient acidic pH states by combining a fast acidic activator with the slow, enzymatic, feedback‐driven generation of a base (dormant deactivator). This transient state can be programmed over orders of magnitude in time. It is coupled to dipeptides to create autonomously self‐regulating, dynamic gels with programmed lifetimes, which are used for fluidic guidance, burst release, and self‐erasing rapid prototyping.     

The Cage Structure of IndanCHF3 is Based on the Cooperative Effects of CH⋅⋅⋅π and CH⋅⋅⋅F Weak Hydrogen Bonds

The structural and energetic features of the C?H???π interaction and the internal dynamics of the CHF₃ group change drastically in going from benzene?CHF₃ to indan?CHF₃, according to the analysis of the rotational spectrum of the latter complex generated in a supersonic expansion.     

On a Model of a Currency Exchange Rate – Local Stability and Periodic Solutions

A delay differential equation is presented which models how the behavior of traders influences the short time price movements of an asset. Sensitivity to price changes is measured by a parameter a. There is a single equilibrium solution, which is non-hyperbolic for all a>0. We prove that for a< 1 the equilibrium is asymptotically stable, and that for a>1 a 2-dimensional global center-unstable manifold connects the equilibrium to a periodic orbit. Its birth at a=1 is not of Hopf type and seems part of a Takens–Bogdanov scenario.     

Janus cylinders at liquid-liquid interfaces

We describe the first study on the self-assembly behavior of Janus cylinders at liquid/liquid interfaces. The Janus cylinders are characterized by a phase separation along the major axis into two hemicylinders of different wettability. The pendant drop technique and microscopic imaging were used to characterize the adsorption behavior and self-assembly of Janus cylinders at perfluorinated oil/dioxane and perfluorinated oil/dimethyl sulfoxide interfaces. According to the evolution of the interfacial tension and a series of TEM images taken during the cylinder adsorption, we will specify the characteristics of early to late stages of the Janus cylinder adsorption at a liquid-liquid interface and discuss the effect of Janus cylinder length and their concentration. We also establish that the broken symmetry of the corona leads to significantly higher interfacial activity as compared to homogeneous core-shell cylinders. The adsorption is characterized by three different adsorption stages: first, free diffusion to the interface, followed by continuous adsorption of cylinders including ordering and domain formation and, finally, additional packing with a rearrangement of domains and formation of a loose multilayer system.     

Optical coherence tomography in biomedical research

Optical coherence tomography (OCT) is a noninvasive, high-resolution, interferometric imaging modality using near-infrared light to acquire cross-sections and three-dimensional images of the subsurface microstructure of biological specimens. Because of rapid improvement of the acquisition speed and axial resolution of OCT over recent years, OCT is becoming increasingly attractive for applications in biomedical research. Therefore, OCT is no longer used solely for structural investigations of biological samples but also for functional examination, making it potentially useful in bioanalytical science. The combination of in vivo structural and functional findings makes it possible to obtain thorough knowledge on basic physiological and pathological processes. Advanced applications, for example, optical biopsy in visceral cavities, have been enabled by combining OCT with established imaging modalities. This report gives an outline of the state of the art and novel trends of innovative OCT approaches in biomedical research in which the main focus is on applications in fundamental research and pre-clinical utilization.     

Hole tunneling and hopping in a Ru(bpy)3(2+)-phenothiazine dyad with a bridge derived from oligo-p-phenylene

A molecular dyad was synthesized in which a Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) photosensitizer and a phenothiazine redox partner are bridged by a sequence of tetramethoxybenzene, p-dimethoxybenzene, and p-xylene units. Hole transfer from the oxidized metal complex to the phenothiazine was triggered using a flash-quench technique and investigated by transient absorption spectroscopy. Optical spectroscopic and electrochemical experiments performed on a suitable reference molecule in addition to the above-mentioned dyad lead to the conclusion that hole transfer from Ru(bpy)(3)(3+) to phenothiazine proceeds through a sequence of hopping and tunneling steps: Initial hole hopping from Ru(bpy)(3)(3+) to the easily oxidizable tetramethoxybenzene unit is followed by tunneling through the barrier imposed by the p-dimethoxybenzene and p-xylene spacers. The overall charge transfer proceeds with a time constant of 41 ns, which compares favorably to a time constant of 1835 ns associated with equidistant hole tunneling between the same donor-acceptor couple bridged by three identical p-xylene units. The combined hopping/tunneling sequence thus leads to an acceleration of hole transfer by roughly a factor of 50 when compared to a pure tunneling mechanism.     

On the weak O-H···halogen hydrogen bond: a rotational study of CH3CHClF···H2O

We measured the molecular beam Fourier transform microwave spectra of six isotopologues of the 1?:?1 adduct of CH(3)CHClF with water. Water prefers to form an O-H···F rather than an O-H···Cl hydrogen bond. This is just the contrary of what was observed in the chlorofluoromethane-water adduct, where an O-H···Cl link was formed (W. Caminati, S. Melandri, A. Maris and P. Ottaviani, Angew. Chem., Int. Ed., 2006, 45, 2438). The water molecule is linked with an O-H···F bridge to the fluorine atom, with r(F···H(w)) = 2.14 ?, and with two C-H···O contacts to the alkyl hydrogens with r(C(1)-H(1)···O(w)) = 2.75 ? and r(C(2)-H(2)···O(w)) = 2.84 ?, respectively. Besides the rotational constants, the quadrupole coupling constants of the chlorine atom have been determined. In addition, information on the internal dynamics has been obtained.     

Surface functionalization of electro-deposited nickel

A new in situ electrochemical method of functionalizing an oxide-free Ni surface is demonstrated using octanethiol. Initial adsorption results in a multilayer molecular film, which blocks both the hydrogen evolution reaction (HER) and re-oxidation of the Ni by ambient oxygen. However, excess octanethiol can be removed by rinsing with ethanol, leaving behind a monolayer that continues to protect against re-oxidation but gives rise to an unexpected enhancement in the HER, with a greater enhancement for longer film formation times. The presence of an octanethiol monolayer on the surface was confirmed by spectroscopic observation of the CH(2), CH(3) and thiolate groups using infra red spectroscopy, while X-ray photo-electron spectroscopy demonstrated the effectiveness of the thiol layer as a barrier to surface oxidation. The electrochemically prepared octanethiol film impedes oxidation of the Ni in air more effectively than a film formed by immersion in a solution of octanethiol in ethanol.     

Determination of heavy metals in suspended matter in the storage lake “Bitterfelder Muldestausee”

Dissolved and particulate trace elements have been determined in 400 samples of both the inflow and the outflow waters of the storage lake “Bitterfelder Muldestausse” in order to investigate the sedimentation of 22 elements transported by the highly polluted Mulde River, an affluent of the river Elbe. Inductively coupled plasma mass spectrometry (ICP-MS) has been used to analyse filtered water samples because of its multielemental capabilities, the excellent detection limits, the wide linear calibration range and the high speed of analysis. A special leaching procedure has been employed for the very low amounts of the suspended matter collected from each water sample. The dissolved material has been also analysed by ICP-MS. Testing of the procedure employed by the analysis of a standard reference material (SRM BCR 146) and use of the standard addition method has resulted in both a good precision (1–7%) and accuracy. Despite the wide variation in the composition of the suspended matter samples the concentrations of the heavy metals in sediment samples and in the suspended matter have been found to be comparable. A balance of sedimentation has been calculated based on the mean values of concentrations of all elements investigated in both the water and suspended matter samples of the inflow and outflow. Results from this first study show that the storage lake acts as a sedimentation trap for Zn, Cu, Pb, Ni, Cr, Cd, U and Co.