Intramolecular energy transfer in a one-dimensional europium tetracyanoplatinate

The one-dimensional, polymeric compound (C15H11N3)Eu(H2O)2(NO3)(Pt(CN)4).CH3CN (1) has been shown to display an efficient donor-acceptor intramolecular energy-transfer (IET) process where ligand donors transfer energy to the Eu (III) acceptor. Single-crystal X-ray diffraction has been used to investigate the structural features of this compound in order to help understand the observed IET process. Crystallographic data: 1, monoclinic, space group P2(1)/c, a = 12.835(1) A, b = 15.239(1) A, c = 13.751(2) A, beta = 105.594(9) degrees , V = 2590.8(5) A(3), and Z = 4 (T = 290 K).     

Expedient Lewis acid catalyzed synthesis of a 3-substituted 5-arylidene-1-methyl-2-thiohydantoin Library

An efficient and rapid solution phase combinatorial synthesis of a 3-substituted 5-arylidene-1-methyl-2-thiohydantoin library was developed. The salient feature for this library production procedure is the addition of the Lewis acid catalyst, indium(III) trifluoromethanesulfonate, which serves to facilitate the direct condensation of aldehydes with 3-substituted 1-methyl-2-thiohydantoins. Use of this Lewis acid catalyst has resulted in faster reaction times, higher conversions and better purity profiles for these condensation reactions as compared to traditional uncatalyzed reactions. The resulting 315 member library of 3-substituted 5-arylidene-1-methyl-2-thiohydantoin is described.     

Synthesis of protein-polymer conjugates

Protein-polymer conjugates are widely employed for applications in medicine, biotechnology and nanotechnology. Covalent attachment of synthetic polymers to proteins improves protein stability, solubility, and biocompatibility. Furthermore, synthetic polymers impart new properties such as self assembly and phase behavior. Polymer attachment at amino acid side-chains and at ligand binding sites is typically exploited. This Emerging Area focuses on synthetic methods to prepare protein-reactive polymers and also employing the protein itself as an initiator for polymerization.     

A computational study of model hydrogen-, halogen-, beryllium- and magnesium-bonded complexes of aziridine derivatives

ABSTRACT

A computational study of the complexes F^?/H₂O…Z-aziridine, Z-aziridine…BeH₂/MgH₂ and F^?/H₂O…Z-aziridine…BeH₂ /MgH₂ (Z = Cl, H, Li) was undertaken in order to investigate the non-covalent interactions operative in the dimers and to assess their interplay in the trimer complexes. The halogen- and hydrogen-bonds between the O and Z atoms in F^?/H₂O…Z-aziridine are enhanced in the trimers by the Be(Mg) bond and vice versa, but the lithium bond is hardly affected. In the trimers containing F^?, the H bond is more dominant than the Be(Mg) bond, whereas the Be(Mg) bond is more dominant in the halogen- and lithium-bonded analogues. On the other hand, the Be(Mg) bond makes the major contribution to the energetic stability of all of the trimers containing H₂O.     

Double pulse quasi-collinear high harmonic generation scheme as a tool for X-ray laser plasma gain probing

We calculate the field distribution based on the vector diffraction theory for a superposition of spirally phase shifted radially polarized beams. Twisted longitudinally polarized field is found in the focal region. The total intensity as well as the polarization components rotates around the beam axis near the focus. Calculation of the Poynting vector at the focal plane shows that the electromagnetic energy is redistributed between different polarization components. Nonzero value of transverse components of the Poynting vector implies the transverse flow of the energy in the focal region.     

Shape-shifting micro- and nanopatterns controlled by temperature

Herein, features that alter their shape to form a different pattern upon an external trigger are described. Electron-beam lithography was used to fabricate micrometer- and nanometer-sized surface immobilized poly(triethylene glycol methacrylate) (pTEGMA) that exhibits significant thermal responsivity; the resulting hydrogels collapsed by up to 95% of their height upon addition of heat. Multicomponent features composed of both the thermoresponsive polymer and nonresponsive poly(ethylene glycol) (PEG) were then prepared. Upon increase in temperature, only the thermally responsive component of the pattern collapsed, causing a significant and predictable alteration in the overall pattern. Reversible micrometer- and nanometer-sized square-to-triangles, squares-to-checkerboards, smiles-to-neutral face, and zeros-to-ones shapes were shown.     

Measuring elastic constants of arbitrarily shaped samples using resonant ultrasound spectroscopy

One of the most important undertakings for materials is the measurement of the elastic behavior. As derivatives of the free energy with respect to atomic displacements, the elastic properties are closely connected to the thermodynamic properties of the material. Elastic behavior is a sensitive probe of the lattice environment in which all solid state phenomena occur, particularly in the vicinity of a phase transition. A useful method for measuring elastic properties is resonant ultrasound spectroscopy (RUS). Some novel materials to which RUS might be applied are often fragile or chemically reactive so that they cannot be polished into the shapes required by conventional RUS; for such cases a finite element method may be used. In this paper a discussion and test of a finite element method for RUS with arbitrarily shaped samples is provided.     

Trapping of Thiol Terminated Acrylate Polymers with Divinyl Sulfone to Generate Well-Defined Semi-Telechelic Michael Acceptor Polymers

Herein we report the synthesis of vinyl sulfone end functionalized PEGylated polymers by reversible addition-fragmentation chain transfer (RAFT) polymerization for conjugation to proteins. Poly(ethylene glycol) methyl ether acrylate (PEGA) was polymerized in the presence of 1-phenylethyl dithiobenzoate with 2,2'-azobis(2-methylpropionitrile) as the initiator to generate well-defined polyPEGAs with number-average molecular weights (M(n)) by gel permeation chromatography (GPC) of 6.7 kDa, 11.8 kDa and 16.1 kDa. Post-polymerization, the majority of polymer chains contained the dithioester functional group at the omega chain end, and the polydispersity indexes (PDI) of the polymers ranged from 1.08 to 1.24. The dithioester was subsequently reduced via aminolysis, and the resulting thiol was trapped with a divinyl sulfone in situ to produce semi-telechelic, vinyl sulfone polyPEGAs with efficiencies ranging between 85% and 99%. It was determined that the retention of vinyl sulfone was directly related to reaction time, with the maximum dithioester being transformed into a vinyl sulfone within 30 minutes. Longer reaction times resulted in slow decomposition of the vinyl sulfone end group. The resulting semi-telechelic vinyl sulfone polymers were then conjugated to a protein containing a free cysteine, bovine serum albumin (BSA). Gel electrophoresis demonstrated that the reaction was highly efficient and that conjugates of increasing size were readily prepared. After polymer attachment, the activity of the BSA was 92% of the unmodified biomolecule.     

The use of piezoelectric film and ultrasound resonance to determine the complete elastic tensor in one measurement.

The ultrasonic and elastic properties of materials are conventionally measured using quartz, lithium niobate, etc., transducers and a pulse-echo technique with the transducer driven at resonance. Problems with the technique include transducer ringing, transducer-sample coupling, parallelism of sample faces, beam diffraction, and the necessity of remounting transducers in order to measure all of the elastic constants. Usually, these problems can be minimized, but with samples that are only a fraction of a millimeter in size, conventional ultrasound measurements become difficult if not impossible. However, nearly all of these problems may be avoided if a resonance technique is used, and all of the elastic constants may be determined with a single measurement. For the broadband response and minimum transducer loading required for a resonance measurement in a small sample, polyvinylidene fluoride (PVDF) piezoelectric film (as thin as 9 microns) is ideally suitable.     

Determination of loads applied perpendicularly to the outer boundary of a ring using coefficients of influence

A procedure is explained to determined the amount of several pairs of diametrical loads applied to the outside boundary of a ring when stresses at selected points of the inside or outside boundaries are known. Coefficients of influence are used, following an approach similar to the one presented in a previous paper. Examples of application are given and the possible increase in precision is shown when the number of points of measurements is larger than the number of loads to be determined.