Biomimetic pH/redox dual stimuli‐responsive zwitterionic polymer block poly(L‐histidine) micelles for intracellular delivery of doxorubicin into tumor cells

A series of pH/redox dual stimuli‐responsive poly(2‐methacryloyloxyethyl phosphorylcholine)₂₅‐block‐poly(l ‐histidine)_n (p[MPC])₂₅‐b‐p[His]_n, n = 20, 35, 50, and 75) copolymers consisting of a pH‐responsive p(His)_n block and a biocompatible phospholipid analog p(MPC) block connected by a redox‐responsive disulfide linker have been synthesized. The block copolymers are self‐assembled into uniform micelles (～100 nm) in which doxorubicin (Dox) is efficiently encapsulated. The in vitro release profile shows an enhanced release of Dox at low pH (5.0) in 10 mM glutathione (GSH). The in vitro cell viability assays performed using various cell lines show that the blank hybrid micelles have no acute or intrinsic toxicity. A pH‐dependent cytotoxicity is observed with the Dox‐loaded micelles, especially at pH 5.0. Moreover, confocal microscopy images and flow cytometry results show the pH‐dependent cellular uptake of Dox‐loaded micelles. Therefore, the Dox‐loaded micelles can be considered a good candidate for cancer therapy. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2061–2070     

Facile synthesis of 4″-O-alkyl-(–)-EGCG derivatives through regioselective deacetylative alkylation

Therapeutic potential of the D-ring methyl ethers of (–)-epigallocatechin-3-gallate [(–)-EGCG] warrants extensive structure–activity relationship study of various D-ring ethers of (–)-EGCG but, for this purpose, efficient synthetic strategy needs to be developed. In this study, efficient preparation of the 4″-O-alkyl-(–)-EGCGs (4a–e) was demonstrated using KI/K₂CO₃-promoted deacetylative alkylation of peracetyl (–)-EGCG, which could be broadly utilized for the preparation of various D-ring alkyl ethers of (–)-EGCG and thereby extensive structure–activity relationship study.     

Critical Heat Flux for Downward Facing Boiling on a Coated Hemispherical Surface

An experimental study was performed to investigate the effect of surface coating on the critical heat flux for downward facing boiling on the outer surface of a hemispherical vessel. Steady-state boiling experiments were conducted in the subscale boundary layer boiling (SBLB) facility using test vessels with metallic microporous coatings to obtain the local boiling curves and the local critical heat flux (CHF) limits. Similar heat transfer performance was observed for microporous aluminum and microporous copper coatings. When compared to the corresponding data without coatings, the boiling curves for the coated vessels were found to shift upward and to the right. This meant that the CHF limit was higher with surface coating and that the minimum film boiling temperatures were located at higher wall superheats. In particular, the microporous coatings were found to enhance the local CHF values appreciably at all angular locations explored in the experiments. Results of the present study showed that the microporous aluminum coating was very durable. Even after many cycles of steady state boiling, the vessel coating remained rather intact, with no apparent changes in color or structure. Although similar heat transfer performance was observed for microporous copper coatings, the latter were found to be much less durable and tended to degrade after several cycles of boiling.     

Configuration Design Sensitivity Analysis of Kinematic Responses of Mechanical Systems∗

Abstract

A continuum-based configuration design sensitivity analysis method is presented for kinematically driven mechanical systems. Configuration design variable for mechanical systems are defined. The 3-1-3 Euler angle is used as the orientation design variable. The reassembly process for a mechanical system after a configuration design change is eliminated by imposing kinematic admissibility conditions of the velocity field. The direct differentiation method is used to derive design sensitivity equations. Numerical examples are presented to demonstrate the validity and effectiveness of the proposed method.     

Photovoltaic devices using semiconducting polymers containing head‐to‐tail‐structured bithiophene,pyrene, and benzothiadiazole derivatives

An alternating copolymer composed of heal‐to‐tail‐structured 3,4′‐dihexyl‐2,2′‐bithiophene (DHBT) and pyrene units [poly(DHBT‐alt‐PYR)] was synthesized using a Stille coupling reaction for use in photovoltaic devices as a p‐type donor. For the reduction of the bandgap energy of poly(DHBT‐alt‐PYR), 4,7‐bis(3′‐hexyl‐2,2′‐bithiophen‐5‐yl)benzo[c][1,2,5]thiadiazole (BHBTBT) units were introduced into the polymer. Poly(DHBT‐co‐PYR‐co‐BHBTBT)s were synthesized using the same polymerization reaction. The synthesized polymers were soluble in common organic solvents and formed smooth thin films after spin casting. The optical bandgap energies of the polymers were obtained from the onset absorption wavelengths. The measured optical bandgap energy of poly(DHBT‐alt‐PYR) was 2.47 eV. As the BHBTBT content in the ter‐polymers increased, the optical bandgap energies of the resulting polymers decreased. The bandgap energies of poly(50DHBT‐co‐40PYR‐co‐10BHBTBT) and poly(50DHBT‐co‐20PYR‐co‐30BHBTBT) were 1.84 and 1.73 eV, respectively. Photovoltaic devices were fabricated with a typical sandwich structure of ITO/PEDOT:PSS/active layer/LiF/Al using the polymers as electron donors and [6,6]‐phenyl C₇₁‐butyric acid methyl ester as the electron acceptor. The device using poly(50DHBT‐co‐20PYR‐co‐30BHBTBT) showed the best performance among the fabricated devices, with an open‐circuit voltage, short‐circuit current, fill factor, and maximum power conversion efficiency of 0.68 V, 5.54 mA/cm², 0.35, and 1.31%, respectively. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Molecular dynamics simulation study on graphene-nanoribbon-resonators tuned by adjusting axial strain

A tunable graphene-nanoribbon (GNR)-resonator was investigated via classical molecular dynamics simulations. Resonance frequencies increased with increasing externally applied gate-force and axial-strain, and could be tuned above several hundred GHz. Tunable resonance frequencies achieved from the gate force were higher than those achieved from the axial-strain. The operating frequencies of GNR-resonators without axial-strain or with small axial-strains were most widely tuned by the gate, and almost linearly increased with increasing mean deflection. As the axial strain increased, the tunable ranges of the GNR-resonators were exponentially decreased, although the operating frequencies increased. GNR-resonators without axial-strain could be applied to wide-range-tuners, whereas GNR-resonators with high axial-strain could be applied to high-frequency-fine-tuners.