Preparation and properties of poly(ethylene oxide) star polymers

Poly(ethylene oxide) (PEO) star polymers were prepared by anionic polymerization of methacryloyl chloride and glyceryl trimethacrylate with sec‐butyllithium in cyclohexane. The ensuing polymers were grafted with poly(ethylene glycol) of molecular weight 400. The final product was washed with methylene chloride and analyzed with infrared spectroscopy, differential scanning calorimetry, and thermogravimetry. Star polymers of PEO were also prepared by anionic polymerization of glycidol with sec‐butyllithium in cyclohexane. The initiator was chosen so as to yield a polymer of 10,000 molecular weight. The resulting polymers were analyzed by nuclear magnetic resonance, infrared spectroscopy, and thermogravimetry. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 322–327, 2003     

Monodisperse nanoparticles of poly(ethylene glycol) macromers and N‐isopropyl acrylamide for biomedical applications

Poly(ethylene glycol)‐based nanoparticles have received significant attention in the field of biomedicine. When they are copolymerized with pH‐ or temperature‐sensitive comonomers, their small size allows them to respond very quickly to changes in the environment, including changes in the pH, ionic strength, and temperature. In addition, the high surface‐to‐volume ratio makes them highly functionalized. In this work, nanoparticles composed of temperature‐sensitive poly(N‐isopropylacrylamide), poly(ethylene glycol) 400 dimethacrylate, and poly(ethylene glycol) 1000 methacrylate were prepared by a thermally initiated, free‐radical dispersion polymerization method. The temperature‐responsive behavior of the hydrogel nanoparticles was characterized by the study of their particle size with photon correlation spectroscopy. The size of the nanoparticles varied from 200 to 1100 nm and was a strong function of the temperature of the system, from 5 to 40°C. The thermal, structural, and morphological characteristics were also investigated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1678–1684, 2003     

Mixed modifier effect in Na2O·K2O·CaO aluminosilicate glasses: Pairwise and ternary interactions

The mixed modifier effect (MME) is one of the most challenging puzzles in the field of oxide glasses, as there exists no universal quantitative theoretical model for accurately describing and predicting the nonlinear deviation of property values. In this paper, pairwise and ternary interactions are examined experimentally to understand the MME in a series of aluminosilicate glasses. By keeping the glass network former concentration constant and adjusting the molar ratios of three network modifiers (Na₂O, K₂O, and CaO), the MMEs in glass transition temperature (T_g), Vickers hardness (H_v), and activation energy (E_a) for aqueous dissolution for each modifier cation are investigated. We examine whether a pairwise interaction model is sufficient, or if ternary interactions also need to be included to predict the MME in these aluminosilicate glass systems. This work reveals that the pairwise model can be used to predict the MME for T_g in complex multiple-modifier glass systems using only two-body interaction factors. However, ternary mixed-modifier interactions are present in other properties such as H_v and E_a.     

Performance characteristics of an axial-flow gas induction impeller

Power number, pressure coefficient, and induced gas flow rate of a novel axial-flow gas induction impeller with large openings for gas flow are reported. The effects of rotational speed, impeller diameter, submergence, and pumping mode are considered in turbulent operation. The pressure coefficient is measured using the reduction in pressure at speeds below the minimum induction speed as well as from the minimum induction speed. The minimum induction speed approach consistently yields lower pressure coefficient values, indicating the existence of impeller exit losses that are required to force gas from the centre of the impeller into the liquid. The induced gas flow rate is modelled using two approaches. The first approach relates the gas flow rate to the available pressure difference, and in this case, the relation is found to be strongly affected by impeller diameter. The second approach is a literature model that likens the induction process to water jet injection. While this approach appears promising, flow measurement device pressure losses make it difficult to definitively evaluate this method.     

Effect of a lattice distortion strategy on the phase transition and properties in KNN-based ceramics

High performance lead-free piezoelectric ceramics are of great importance to the sustainable development of the environment. To obtain excellent comprehensive performance KNN-based lead-free piezoelectric ceramics, a lattice distortion strategy combined with domain configuration was designed in (1 − x)K_0.5Na_0.5Nb_0.95Sb_0.05O₃–xCaHfO₃ ((1 − x)KNNS–xCH) system by introduced Ca²⁺ into the A-site and Hf⁴⁺ into the B-site. The results demonstrated that the rhombohedral–orthorhombic–tetragonal polymorphic phase boundary (PPB) was constructed in 0.02 ≤ x ≤ 0.04 and significant lattice distortion occurred in R- and T-phase. Moreover, the 0.97KNNS–0.03CH sample exhibited excellent electrical performance (e.g., k_p ∼ 43.8%, d^*₃₃ ∼ 478.6 pm/V, and d₃₃ ∼ 392 pC/N) together with a high Curie temperature (T_C ∼ 295°C) profited from the PPB and domain configurations. The ceramics also showed the optimal thermal stability, which was beneficial to promote the development of KNN-based ceramics.     

Macrocyclization of Organo‐Peptide Hybrids through a Dual Bio‐orthogonal Ligation: Insights from Structure–Reactivity Studies

Macrocycles constitute an attractive structural class of molecules for targeting biomolecular interfaces with high affinity and specificity. Here, we report systematic studies aimed at exploring the scope and mechanism of a novel chemo‐biosynthetic strategy for generating macrocyclic organo‐peptide hybrids (MOrPHs) through a dual oxime‐/intein‐mediated ligation reaction between a recombinant precursor protein and bifunctional, oxyamino/1,3‐amino‐thiol compounds. An efficient synthetic route was developed to access structurally different synthetic precursors incorporating a 2‐amino‐ mercaptomethyl‐aryl (AMA) moiety previously found to be important for macrocyclization. With these compounds, the impact of the synthetic precursor scaffold and of designed mutations within the genetically encoded precursor peptide sequence on macrocyclization efficiency was investigated. Importantly, the desired MOrPHs were obtained as the only product from all the different synthetic precursors probed in this study and across peptide sequences comprising four to 15 amino acids. Systematic mutagenesis of the “i?1” site at the junction between the target peptide sequence and the intein moiety revealed that the majority of the 20 amino acids are compatible with MOrPH formation; this enables the identification of the most and the least favorable residues for this critical position. Furthermore, interesting trends with respect to the positional effect of conformationally constrained (Pro) and flexible (Gly) residues on the reactivity of randomized hexamer peptide sequences were observed. Finally, mechanistic investigations enabled the relative contributions of the two distinct pathways (side‐chain→C‐end ligation versus C‐end→side‐chain ligation) to the macrocyclization process to be dissected. Altogether, these studies demonstrate the versatility and robustness of the methodology to enable the synthesis and diversification of a new class of organo‐peptide macrocycles and provide valuable structure–reactivity insights to inform the construction of macrocycle libraries through this chemo‐biosynthetic strategy.     

Characterization of Thiol‐Ene Crosslinked PEG Hydrogels

The properties of synthetic hydrogels can be tuned to address the needs of many tissue‐culture applications. This work characterizes the swelling and mechanical properties of thiol‐ene crosslinked PEG hydrogels made with varying prepolymer formulations, demonstrating that hydrogels with a compressive modulus exceeding 600 kPa can be formed. The amount of peptide incorporated into the hydrogel is shown to be proportional to the amount of peptide in the prepolymer solution. Cell attachment and spreading on the surface of the peptide‐functionalized hydrogels is demonstrated. Additionally, a method for bonding distinct layers of cured hydrogels is used to create a microfluidic channel.

     

Experimental Phase Diagram Determination and Thermodynamic Assessment of the CeO2‐Gd2O3‐CoO System

New phase diagram data and a thermodynamic assessment of the CeO‐Gd₂O₃‐CoO system using the CALPHAD approach are presented. This information is needed to understand the surprisingly low sintering temperature (950°C–1050°C) of CeO₂‐based materials doped with small amounts of transition metal oxide (e.g., CoO). Experimental phase equilibria between 1100°C and 1300°C are reported based on the analysis of annealed and molten samples. No isolated compound exists in the ternary. At 1300°C the Co solubility in the ternary compounds Ce_1?x?yGd_xCo_yO_2?x/2?y (fluorite) is 2.7 mol% and is less than 1 mol% in the Gd_2?xCe_xO_3+x/2 (bixbyite). The Ce solubility in the perovskite GdCoO_3?δ was found to be 1 mol%. The lowest temperature eutectic melt in the ternary has a composition of 57.2 mol% Co and 41.1 mol% Gd melting at an onset temperature of 1303 ± 5°C, which is close to the binary eutectic in the Gd₂O₃‐CoO system at 60 ± 2 mol% Co and 1348 ± 1°C.     

Impact of Site-Specific Benzo[a]Pyrene Diol Epoxide-dG Lesions at or near Single/Double-Strand DNA Junctions on DNA Bending

Adducts derived from the binding of the (+)-7R,8S,9S,10R and (?)-7S,8R,9R,10S enantiomers of r7,t8-dihydrodiol-t9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE) to 2′-deoxyguanosine residues in DNA are known to induce mutations due to error-prone DNA replication. Because the conformational properties of these lesions may be important in these phenomena, we have examined the effects of the stereoisomeric (+)- and (?)-trans-anti-[BP]-N ²-dG lesions positioned site-specifically at or near primer/template oligonucleotide junctions on DNA bending using high resolution gel electrophoresis. Remarkable differences in electrophoretic mobilities μ are observed in the two adducts derived from the tumorigenic (+)-anti-BPDE, and the non-tumorigenic (?)-anti-BPDE enantiomer. With the (+)-trans lesion positioned on the template strand adjacent to the 3′-end of the primer strand, a remarkable decrease in μ is observed. This suggests the existence of a bend at the single strand-double strand junction. Only modest decreases in μ are observed in the case of the (?)-trans lesion, or when the 3′-end is opposite to, or more distant from the lesion site. These observations are discussed in terms of the known NMR solution structures of these lesions in the same sequence context, and the properties of primer/template DNA in polymerases.     

Characterization of a dimer preparation method for nanoscale organic aerosol

Nanoscale dimers have application in studies of aerosol physicochemical properties such as aerosol viscosity. These particle dimers can be synthesized using the dual tandem differential mobility analyzer (DTDMA) technique, wherein oppositely charged particle streams coagulate to form dimers that can be isolated using electrostatic filtration. Although some characterization of the technique has been published, a detailed thesis on the modes and theory of operation has remained outside the scope of prior work. Here, we present new experimental data characterizing the output DTDMA size distribution and the physical processes underlying its apparent modes. Key experimental limitations for both general applications and for viscosity measurements are identified and quantified in six distinct types of DTDMA experiments. The primary consideration is the production of an adequate number of dimers, which typically requires high mobility-selected number concentration in the range 25,000–100,000?cm^?3. The requisite concentration threshold depends upon the rate of spontaneous monomer decharging, which arises predominately from interactions of the aerosol with ionizing radiation within the coagulation chamber and is instrument location dependent. Lead shielding of the coagulation chamber reduced the first-order decharging constant from ～2.0?×?10^?5 s^?1 to ～0.8?×?10^?5 s^?1 in our laboratory. Dimer production at monomer diameters less than 40?nm is hindered by low bipolar charging efficiency. Results from the characterization experiments shed light on design considerations for general applications and for characterization of viscous aerosol phase transitions.

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