Circular Upcycling of Bottlebrush Thermosets

The inability to re-process thermosets hinders their utility and sustainability. An ideal material should combine closed-loop recycling and upcycling capabilities. This trait is realized in polydimethylsiloxane bottlebrush networks using thermoreversible Diels–Alder cycloadditions to enable both reversible disassembly into a polymer melt and on-demand reconfiguration to an elastomer of either lower or higher stiffness. The crosslink density was tuned by loading the functionalized networks with a controlled fraction of dormant crosslinkers and crosslinker scavengers, such as furan-capped bis-maleimide and anthracene, respectively. The resulting modulus variations precisely followed the stoichiometry of activated furan and maleimide moieties, demonstrating the lack of side reactions during reprocessing. The presented circularity concept is independent from the backbone or side chain chemistry, making it potentially applicable to a wide range of brush-like polymers.     

Protein microarrays and quantum dot probes for early cancer detection

We describe here a novel approach for detection of cancer markers using quantum dot protein microarrays. Both relatively new technologies; quantum dots and protein microarrays, offer very unique features that together allow detection of cancer markers in biological specimens (serum, plasma, body fluids) at pg/ml concentration. Quantum dots offer remarkable photostability and brightness. They do not exhibit photobleaching common to organic fluorophores. Moreover, the high emission amplitude for QDs results in a marked improvement in the signal to noise ratio of the final image. Protein microarrays allow highly parallel quantitation of specific proteins in a rapid, low-cost and low sample volume format. Furthermore the multiplexed assay enables detection of many proteins at once in one sample, making it a powerful tool for biomarker analysis and early cancer diagnostics.

In a series of multiplexing experiments we investigated ability of the platform to detect six different cytokines in protein solution. We were able to detect TNF-, IL-8, IL-6, MIP-1β, IL-13 and IL-1β down to picomolar concentration, demonstrating high sensitivity of the investigated detection system.

We have also constructed and investigated two different models of quantum dot probes. One by conjugation of nanocrystals to antibody specific to the selected marker—IL-10, and the second by use of streptavidin coated quantum dots and biotinylated detector antibody. Comparison of those two models showed better performance of streptavidin QD–biotinylated detector antibody model. Data quantitated using custom designed computer program (CDAS) show that proposed methodology allows monitoring of changes in biomarker concentration in physiological range.     

Layer-by-layer deposition of rhenium-containing hyperbranched polymers and fabrication of photovoltaic cells

Multilayer thin films were prepared by the layer-by-layer (LBL) deposition method using a rhenium-containing hyperbranched polymer and poly[2-(3-thienyl)ethoxy-4-butylsulfonate] (PTEBS). The radii of gyration of the hyperbranched polymer in solutions with different salt concentrations were measured by laser light scattering. A significant decrease in molecular size was observed when sodium trifluoromethanesulfonate was used as the electrolyte. The conditions of preparing the multilayer thin films by LBL deposition were studied. The growth of the multilayer films was monitored by absorption spectroscopy and spectroscopic ellipsometry, and the surface morphologies of the resulting films were studied by atomic force microscopy. When the pH of a PTEBS solution was kept at 6 and in the presence of salt, polymer films with maximum thickness were obtained. The multilayer films were also fabricated into photovoltaic cells and their photocurrent responses were measured upon irradiation with simulated air mass (AM) 1.5 solar light. The open-circuit voltage, short-circuit current, fill factor, and power conversion efficiency of the devices were 1.2 V, 27.1 mu A cm(-2), 0.19, and 6.1x10(-3) %, respectively. The high open-circuit voltage was attributed to the difference in the HOMO level of the PTEBS donor and the LUMO level of the hyperbranched polymer acceptor. A plot of incident photon-to-electron conversion efficiency versus wavelength also suggests that the PTEBS/hyperbranched polymer junction is involved in the photosensitization process, in which a maximum was observed at approximately 420 nm. The relatively high capacitance, determined from the measured photocurrent rise and decay profiles, can be attributed to the presence of large counter anions in the polymer film.     

Three-component one-pot synthesis of fused uracils – pyrano[2,3-d]‐pyrimidine-2,4-diones

5-Arylidene-N,N-dimethylbarbituric acids undergo smooth hetero-Diels-Alder reactions with enol ethers to afford cis and trans diastereoisomers of 7-alkoxy-5-aryl-2H-pyrano[2,3-d]pyrimidine-2,4-diones in excellent yields (84–95%). Cycloadducts with cis-configuration were the major products. Three-component one-pot reactions of N,N-dimethylbarbituric acid, aromatic and heteroaromatic aldehydes, and enol ethers in the presence of piperidine gave uracils also in very good yields (87–95%). The structure of the cycloadducts is discussed in terms of configuration and preferred conformation. Correspondence: Aleksandra Pałasz, Department of Organic Chemistry, Jagiellonian University, Kraków, Poland.     

Determination of glass temperature of polymers by inverse gas chromatography

Inverse gas chromatography (IGC) is an attractive technique for polymer characterization due to possible simultaneous determination of various physicochemical properties of polymer systems merely from retention times of selected sorbates. The technique is especially advantageous to polymers that cannot be characterized by conventional methods. In this review, the utilization of the method for glass transition determination of homopolymers, copolymers and polymer blends is described. Advantages and drawbacks of the IGC method over traditionally used methods for glass transition temperature determination is discussed, along with the most important parameters that influence the precision and accuracy of the glass transition temperature (T(g)) measurements.     

Modified Pechini synthesis of Na3Ce(PO4)2 and thermochemistry of its phase transition

Effect of the synthesis conditions of Pechini technique on crystallinity and purity of Na₃Ce(PO₄)₂ compound was investigated. Nano-sized cerium-sodium phosphate obtained when EDTA was used as an additional chelating agent for Ln³⁺. The total enthalpy change of Na₃Ce(PO₄)₂ phase transition was determined as 14.2±0.7 kJ mol⁻¹ for sample synthesized by conventional solid-solid reaction. The phase transition process was confirmed to occur at 1060°C or in temperature range 920–1060°C depending on thermal treatment of powders.     

Liquid-vapor equilibrium of the systems butylmethylimidazolium nitrate-CO2 and hydroxypropylmethylimidazolium nitrate-CO2 at high pressure: influence of water on the phase behavior

Ionic liquids (IL) are receiving increasing attention due to their potential as "green" solvents, especially when used in combination with SC-CO2. In this work liquid-vapor equilibria of binary mixtures of CO2 with two imidazolium-based ionic liquids (IL) with a nitrate anion have been experimentally determined: butylmethylimidazolium nitrate (BMImNO3) and hydroxypropylmethylimidazolium nitrate (HOPMImNO3), using a Cailletet apparatus that operates according to the synthetic method. CO2 concentrations from 5 up to 30 mol % were investigated. It was found that CO2 is substantially less soluble in HOPMImNO3 than in BMImNO3. Since these ILs are very hygroscopic, water easily can be a major contaminant, causing changes in the phase behavior. In case these Ils are to be used in practical applications, for instance, together with CO2 as a medium in supercritical enzymatic reactions, it is very important to have quantitative information on how the water content will affect the phase behavior. This work presents the first systematic study on the influence of water on the solubility of carbon dioxide in hygroscopic ILs. It was observed that the presence of water reduces the absolute solubility of CO2. However, at fixed ratios of CO2/IL, the bubble point pressure remains almost unchanged with increasing water content. In order to explain the experimental results, the densities of aqueous mixtures of both ILs were determined experimentally and the excess molar volumes calculated.     

The unusual binding abilities of the His-analogue of Arg-vasopressin towards Cu2+

A new vasopressin analogue, [His(1,6)]AVP, was synthesized and characterized by potentiometric measurements as well as by UV-Vis, CD and EPR spectroscopy. At the physiological pH the peptide forms a stable complex with Cu(2+) ions which is characterized by the {NH(2), N(Im), N(Im(macrochelate))} binding mode. The replacement of both Cys by His residues in the vasopressin sequence results in a very significant increase in the efficiency of Cu(2+) binding.     

De novo refolding and aggregation of insulin in a nonaqueous environment: an inside out protein remake

While thermodynamic penalties associated with protein-water interactions are the key driving force of folding, perturbed hydration of destabilized protein molecules may trigger aggregation, which in vivo often causes cellular and histological damage. Here we show, that the denatured state of an alpha-helical protein, insulin, converts to a non-native beta-sheet-rich structure upon de novo "refolding" in an anhydrous environment. The beta-pleated conformer precipitates from solutions of DMSO-denatured insulin upon dilution with chloroform. DMSO destroys hydrogen bond network of the native protein acting as a strong acceptor of main chain hydrogen bonds. Upon the addition of chloroform, which is a weak hydrogen bond donor per se, competitive hydrogen bonds between DMSO and chloroform are formed. This leads to the release of unfolded insulin molecules. In the absence of water, the imminent saturation of polypeptide's dandling hydrogen bonds does not produce the native and predominantly alpha-helical state but a beta-sheet-rich structure, which is morphologically and spectrally distinct from insulin amyloid fibrils. Unlike insulin fibrils, the beta-sheet conformer is metastable and refolds spontaneously to the native form in an aqueous environment. This implies that "folding" in the absence of water results in inefficient burial of hydrophobic side-chains, and thermodynamic frustration at the water-protein interface.