Lanthanide macrocyclic quinolyl conjugates as luminescent molecular-level devices.

The Eu(III) tetraazamacrocyclic complexes [Eu.1] and [Eu.2], and the Tb(III) and Yb(III) complexes [Tb.1] and [Yb.2], have been synthesized as luminescent molecular-level devices. The Eu complexes exhibit unique dual pH switching behavior in water under ambient conditions. The delayed Eu emission is reversibly switched on in acid, with an enhancement factor of several hundred for [Eu.1]. These observations are consistent with the protonation of the quinoline aryl nitrogen moiety (pK(a) approximately equal to 5.9 for [Eu.1]). The fluorescence emission spectra of these complexes are unaffected by acid, but pronounced changes occur in alkaline solution due to the deprotonation of the aryl amide nitrogen (pK(a) approximately 9.4 for [Eu.1]). [Tb.1] shows a more intriguing pH dependence; Tb emission is switched "on" only in the presence of H+ and in the absence of molecular oxygen, whereas the fluorescence emission properties are similar to those observed with [Eu.1]. This behavior can be conveniently described as a molecular-level logic gate, corresponding to a two-input INHIBIT function, A wedge B'. The analogous [Yb.2] complex shows no such pH or O(2) dependence.     

Scaling laws in simple and complex proteins: size scaling effects associated with domain number and folding class

The native states of the most compact globular proteins have been described as being in the so-called “collapsed-polymer regime,” characterized by the scaling law R _g ~ n ^ν, where R _g is radius of gyration, n is the number of residues, and ν ≈ 1/3. However, the diversity of folds and the plasticity of native states suggest that this law may not be universal. In this work, we study the scaling regimes of: (i) one to four-domain protein chains, and (ii) their constituent domains, in terms of the four major folding classes. In the case of complete chains, we show that size scaling is influenced by the number of domains. For the set of domains belonging to the all-α, all-β, α/β, and α?+?β folding classes, we find that size-scaling exponents vary between 0.3?≤?ν?≤?0.4. Interestingly, even domains in the same folding class show scaling regimes that are sensitive to domain provenance, i.e., the number of domains present in the original intact chain. We demonstrate that the level of compactness, as measured by monomer density, decreases when domains originate from increasingly complex proteins.     

Proper Orthogonal Decomposition of Flexible Clap and Fling Elastic Motions via High-Speed Deformation Measurements

Many complex unsteady mechanisms are thought to facilitate the high efficiency and agility commonly observed in small biological flyers. One of these, the flexible clap and fling maneuver, has not been extensively studied; an experimental characterization is the focus of this work. The clap–fling mechanism is approximated with a single flexible membrane flapping wing, replacing the symmetry plane between two wings with a splitter plate simulating the pair wing. This produces a complex vibro-impact aeroelastic problem, the deformation resulting from which is measured with a high-speed visual image correlation system. A low-dimensional representation of the ensuing large data set is obtained with proper orthogonal decomposition. The POD modes, and the relative importance of each, can help elucidate crucial mechanisms and relationships within the flapping system, and are computed for various membrane wing structures and flapping frequencies, with or without the presence of the splitter plate.     

A radioanalytical phantom for assessing the efficacy of electrokinetic decontamination of entrained radioactivity within concrete media

A phantom for the evaluation of electrokinetic remediation of radioactive species from water saturated concrete is described. The phantom has been designed to be a general analogue for environments where structural concrete is saturated by radioactive aqueous solutions and where electrokinetic remediation may be deployed. It is also a specific analogue for the walls of storage ponds for legacy spend nuclear fuel pins where the pond water comprises a large volume of hazardous active waste that may penetrate the pond wall. The fabricated phantom was evaluated using a fixed electrical potential to monitor the rate of cationic transport of K⁺ through concrete samples of different thickness (20 and 35 mm respectively). Results of the evaluation show K⁺ diffusion coefficients of 5.20 × 10^?13 and 7.61 × 10^?13 m² s^?1 for the 20 mm and 35 mm samples, consistent with those seen in literature for the transport of caesium through concrete of similar thickness. The phantom offers a means of experimental validation of computational electrokinetic models as well as providing a basis to test the effects of electrode material on ionic transport rates, to interrogate the effects of pH on all components of the system, and as a basis for instruction, education and training in nuclear decommissioning and waste treatment.     

Orthogonal Cationic and Radical RAFT Polymerizations to Prepare Bottlebrush Polymers

An orthogonal combination of cationic and radical RAFT polymerizations is used to synthesize bottlebrush polymers using two distinct RAFT agents. Selective consumption of the first RAFT agent is used to control the cationic RAFT polymerization of a vinyl ether monomer bearing a secondary dormant RAFT agent, which subsequently allows side‐chain polymers to be grafted from the pendant RAFT agent by a radical‐mediated RAFT polymerization of a different monomer, thus completing the synthesis of bottlebrush polymers. The high efficiency and selectivity of the cationic and radical RAFT polymerizations allow both polymerizations to be conducted in one‐pot tandem without intermediate purification.     

Enantioselective binding of α-pinene and of some cyclohexanetriol derivatives by cyclodextrin hosts: A molecular modeling study

We have used molecular modeling to investigate the enantioselective separation of the monoterpene α-pinene on permethylated β-cyclodextrin and on α-cyclodextrin and the enantioselective separation of three cyclohexanetriol derivatives on permethylated β-cyclodextrin. Using the Consistent Valence Force Field (CVFF) from Insight/Discover, we have carried out systematic rigid-body docking grid searches on each of the optical antipodes of the organic guest molecules interacting with the cyclodextrins, followed by minimizations of the low-energy docked structures. A statistical mechanical analysis of the minimized energies yields data that agree in four out of five cases with the experimental elution order of enantiomers. The computed energies of the rigid-body docking before minimizations do not agree with the experimental results, suggesting that a conformational induced fit of the cyclodextrins upon binding of the organic guests may be involved in the mechanism of the chiral recognition. © 1996 by John Wiley & Sons, Inc.     

Applications of esr techniques to the study of free radical processes and kinetics in acrylic polymerizations

Electron spin resonance (ESR) techniques have been applied to a detailed study of batch and semicontinuous emulsion polymerization of methyl methacrylate; butyl acrylate and styrene have been briefly studied. Quenching of samples from the polymerization reactor followed by ESR analysis are useful, but we have developed continuous flow techniques which are preferable in many cases. ESR techniques can provide valuable information relating to the nature of free radical reactions, the concentration of propagating free radicals, and the kinetic processes in these reactions. Direct ESR analysis is most valuable but is not applicable to all systems. Spin trapping techniques can be useful for systems not accessible by direct analysis.