Concertos, trombone, orchestra, B♭ major; arr.

score and part. 34 cm

Mechanisms of Uranyl Sequestration by Hydrotalcite

Since the advent of large-scale U mining, processing, and enrichment for energy or weapons production, efficient capture and disposal of U, transuranics, and daughter radionuclides has constituted an omnipresent challenge. In this study, we investigated uranyl (UO₂²⁺) sequestration by hydrotalcite (HTC) as a coprecipitation or surface adsorption reaction scenario. The master variables of the study were pH (7.0 and 9.5) and CO₂ content during the reactions (CO₂-rich, CO₂r vs CO₂-depleted, CO₂p). In addition, we compared the outcomes of U–HTC coprecipitation reactions between pristine salt precursors and barren U mine wastewater (lixiviant). Extended X-ray absorption fine structure spectra revealed that uranyl adsorbs on the HTC surface as inner-sphere complexes in CO₂r and CO₂p systems with U–Mg/Al interatomic distances of ∼3.20 and ∼3.35 Å indicative of single-edge (¹E) and double-edge (²E) sharing complexes, respectively. Partial coordination of uranyl by carbonate ligands in CO₂r systems does not appear to hinder surface complexation, suggesting ligand-exchange mechanisms to be operative for the formation of inner-sphere surface complexes. Uranyl symmetry is maintained when coprecipitated with Al and Mg from synthetic or barren lixiviant solutions, precluding incorporation into the HTC lattice. Uranyl ions, however, are surrounded by up to 3–5 Mg/Al atoms in coprecipitated samples interfering with HTC crystal growth. Future research should explore the potential of Fe­(II) or Mn­(II) to reduce U­(VI) to U­(V), which is conducive for U incorporation into octahedral crystal lattice positions of the hydroxide sheet

Angiotensin II–Induced Leukocyte Adhesion on Human Coronary Endothelial Cells Is Mediated by E-Selectin

Abstract Clinical data suggest a link between the activation of the renin-angiotensin system and cardiovascular ischemic events. Leukocyte accumulation in the vessel wall is a hallmark of early atherosclerosis and plaque progression. E-Selectin, vascular cell adhesion molecule-1 (VCAM-1), and intercellular adhesion molecule-1 (ICAM-1) are adhesion molecules participating in mediating interactions between leukocytes and endothelial cells and have been found to be expressed in atherosclerotic plaques. We investigated whether angiotensin II, the effector of the renin-angiotensin system, influences the endothelial expression of E-selectin, VCAM-1, and ICAM-1. In coronary endothelial cells derived from explanted human hearts, angiotensin II (10 −11 to 10 −5 mol/L) induced a concentration-dependent increase in E-selectin expression. The effect was measured by cell ELISA and duplex reverse-transcription polymerase chain reaction (RT-PCR) and reached its maximum at 10 −7 mol/L. Angiotensin II induced only a small increase in E-selectin expression in cardiac microvascular endothelial cells. VCAM-1 and ICAM-1 were not affected by angiotensin II stimulation. In addition, the effect of angiotensin II–induced E-selectin expression on leukocyte adhesion was quantified under flow conditions. Angiotensin II (10 −7 mol/L) increased leukocyte adhesion significantly to 67% of the maximal effect by tumor necrosis factor-α at a wall shear stress of 2 dyne/cm 2 . This adhesion was found to be E-selectin dependent, as demonstrated by blocking antibodies. The AT 1 -receptor antagonist DUP 753 significantly reduced E-selectin–dependent adhesion, whereas the AT 2 -receptor antagonist PD 123177 had no inhibitory effect. In addition, only AT 1 -receptor, but not AT 2 -receptor, mRNA could be detected by RT-PCR in coronary endothelial cells. Therefore, it is suggested that AT 1 receptors mediate the effects of angiotensin II on E-selectin expression and leukocyte adhesion on coronary endothelial cells

Photochemistry and Electron Transfer Kinetics in a Photocatalyst Model Assessed by Marcus Theory and Quantum Dynamics

The present computational study aims at unraveling the competitive photoinduced electron transfer (ET) kinetics in a supramolecular photocatalyst model. Detailed understanding of the fundamental processes is essential for the design of novel photocatalysts in the scope of solar energy conversion that allows unidirectional ET from a light-harvesting photosensitizer to the catalytically active site. Thus, the photophysics and the photochemistry of the bimetallic complex <b>RuCo</b>, [(bpy)₂Ru^II(tpphz)­Co^III(bpy)₂]⁵⁺, where excitation of the ruthenium­(II) moiety leads to an ET to the cobalt­(III), were investigated by quantum chemical and quantum dynamical methods. Time-dependent density functional theory (TDDFT) allowed us to determine the bright singlet excitations as well as to identify the triplet states involved in the photoexcited relaxation cascades associated with charge-separation (CS) and charge-recombination (CR) processes. Diabatic potential energy surfaces were constructed for selected pairs of donor–acceptor states leading to CS and CR along linear interpolated Cartesian coordinates to study the intramolecular ET via Marcus theory, a semiempirical expression neglecting an explicit description of the potential couplings and quantum dynamics (QD). Both Marcus theory and QD predict very similar rate constants of 1.55 × 10¹² – 2.24 × 10¹³ s^–1 and 1.21 × 10¹³–7.59 × 10¹³ s^–1 for CS processes, respectively. ET rates obtained by the semiempirical expression are underestimated by several orders of magnitude; thus, an explicit consideration of electronic coupling is essential to describe intramolecular ET processes in <b>RuCo</b>

Magnetic Biocomposites for Remote Melting

A new approach toward the fabrication of biocompatible composites suitable for remote melting is presented. It is shown that magnetite nanoparticles (MNP) can be embedded into a matrix of biocompatible thermoplastic dextran esters. For that purpose, fatty acid esters of dextran with adjustable melting points in the range of 30–140 °C were synthesized. Esterification of the polysaccharide by activation of the acid as iminium chlorides guaranteed mild reaction conditions leading to high quality products as confirmed by FTIR- and NMR spectroscopy as well as by gel permeation chromatography (GPC). A method for the preparation of magnetically responsive bionanocomposites was developed consisting of combined dissolution/suspension of the dextran ester and hydrophobized MNPs in an organic solvent followed by homogenization with ultrasonication, casting of the solution, drying and melting of the composite for a defined shaping. This process leads to a uniform distribution of MNPs in nanocomposite as revealed by scanning electron microscope. Samples of different geometries were exposed to high frequency alternating magnetic field. It could be shown that defined remote melting of such biocompatible nanocomposites is possible for the first time. This may lead to a new class of magnetic remote control systems, which are suitable for controlled release applications or self-healing materials

Tetra-Sensitive Graft Copolymer Gels as Active Material of Chemomechanical Valves

Stimuli-responsive hydrogels combine sensor and actuator properties by converting an environmental stimulus into mechanical work. Those materials are highly interesting for applications as a chemomechanical valve in microsystem technologies. However, studies about key characteristics of hydrogels for this application are comparatively rare, and further research is needed to emphasize their real potential. The first part of this study depicts the synthesis of grafted hydrogels based on a poly­(<i>N</i>-isopropylacrylamide) backbone and pH-sensitive poly­(acrylic acid) graft chains. The chosen approach of grafted hydrogels provides the preparation of multiresponsive hydrogels, which retain temperature sensitivity besides being pH-responsive. A pronounced salt and solvent response is additionally achieved. Key characteristics for an application as a chemomechanical valve of the graft hydrogels are revealed: (1) independently addressable response to all stimuli, (2) significant volume change, (3) sharp transition, (4) reversible swelling–shrinking behavior, and (5) accelerated response time. To prove the concept of multiresponsive hydrogels for flow control, a <i>net</i>-poly­(<i>N</i>-acrylamide)-<i>g</i>-poly­(acrylic acid) hydrogel containing 0.6 mol % poly­(acrylic acid)-vinyl is employed as active material for chemomechanical valves. Remarkably, the chemomechanical valve can be opened and closed in a fluidic platform with four different stimuli

Fate of Photoexcited Molecular Antennae - Intermolecular Energy Transfer versus Photodegradation Assessed by Quantum Dynamics

The present computational study aims to unravel the competitive photoinduced intermolecular energy transfer and electron transfer phenomena in a light-harvesting antenna with potential applications in dye-sensitized solar cells and photocatalysis. A series of three thiazole dyes with hierarchically overlapping emission and absorption spectra, embedded in a methacrylate-based polymer backbone, is employed to absorb light over the entire visible region. Intermolecular energy transfer in such antenna proceeds via energy transfer from dye-to-dye and eventually to a photosensitizer. Initially, the ground and excited state properties of the three push–pull-chromophores (e.g., with respect to their absorption and emission spectra as well as their equilibrium structures) are thoroughly evaluated using state-of-the-art multiconfigurational methods and computationally less demanding DFT and TDDFT simulations. Subsequently, the potential energy landscape for the three dyads, formed by the π-stacked dyes as occurring in the polymer environment, is investigated along linear-interpolated internal coordinates to elucidate the photoinduced dynamics associated with intermolecular energy and electron transfer processes. While energy transfer among the dyes is highly desired in such antenna, electron transfer, or rather a light-induced redox chemistry, leading to the degradation of the chromophores, is disadvantageous. We performed quantum dynamical wavepacket calculations to investigate the excited state dynamics following initial light-excitation. Our calculations reveal for the two dyads with adjusted optical properties exclusively efficient intermolecular energy transfer within 200 fs, while in the case of the third dyad intermolecular electron transfer dynamics can be observed. Thus, this computational study reveals that statistical copolymerization of the individual dyes is disadvantageous with respect to the energy transfer efficiency as well as regarding the photostability of such antenna