Structural symmetry breaking of silicon‐containing poly(amide‐imide) oligomers and its relation to electrical conductivity and Raman‐active vibrations

Optically active poly(amide‐imide) oligomers were synthesized by direct polycondensation between an aromatic diamine and a dicarboxylic acid both containing a diphenylsilylene unit. The reaction was carried out using triphenyl phosphite/pyridine in the presence of CaCl₂ and N‐methyl‐2‐pyrrolidone as solvent. Oligomers were obtained in good yields and showed high solubility in common aprotic polar solvents. The precursors, monomers and poly(amide‐imide) oligomers were characterized using elemental analysis and Fourier transform infrared and NMR (¹H, ¹³C, ²⁹Si) spectroscopy. Additionally, the main vibrations of the functional groups (C?O, C?C or N? H) in the oligomers with respect to temperature were characterized using Raman spectroscopy. The glass transition temperature was determined by studying the Raman spectra and corroborated using differential scanning calorimetry. The thermal stability was studied using thermogravimetric analysis. The molecular mass of the compounds was obtained from matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry and their optical properties were analyzed using UV‐visible diode array spectrophotometry. The electronic properties of the oligomers as well as the delocalization of charge carriers within their structures were analyzed using conductance‐voltage curves, which showed that these materials are excellent candidates for integrated optoelectronic applications. Copyright © 2011 Society of Chemical Industry     

Thiophene‐ and silarylene‐containing polyesters. Resonance effect on conductivity after polarization in an external electric field

Polyesters were synthesized by direct polycondensation of thiophene‐2,5‐dicarboxylic acid and five different silarylene‐containing diphenols using a tosyl chloride/pyridine/N,N‐dimethylformamide system as a condensing agent. Polymers were obtained in good yields and were characterized using Fourier transform infrared and NMR (¹H, ¹³C, 135‐DEPT and ²⁹Si) spectroscopy and elemental analysis. All polymers were completely soluble in aprotic organic polar solvents such as dimethylformamide, dimethylsulfoxide and N‐methyl‐2‐pyrrolidone. The range of effective mass of the polymers (m/z) was 1 × 10⁵–2 × 10⁵, determined using electrospray ionization mass spectrometry. Asymmetry and steric hindrance prevented dense packing of the polymeric chains, showing glass transition temperatures between ? 78 and ? 51 °C and loss of thermal stability at 177–199 °C (10% weight loss). Additionally, the melting points of the polyesters were found to be in the range 62–67 °C. Because of this, the samples were semi‐solid at room temperature. The optical band gaps of the polymers were observed between 4.54 and 4.48 eV, corresponding in all cases to insulator behavior. The molecular structure of the samples was studied using X‐ray diffraction, showing a degree of order that was associated with two monoclinic lattices. Additionally, the conductivity was studied using a two‐point method with contacts on top of polymer films. Prior to the electrical measurement, the samples were polarized in an external electric field of 0.8 to 6.4 V cm^?1, and the alignment of the dipoles increased the electrical conductivity. Copyright © 2012 Society of Chemical Industry     

Processing and properties of syntactic foams reinforced with carbon nanotubes

This article presents synthesis and mechanical characterization of carbon nanotube (CNT)‐reinforced syntactic foams. Following a dispersion approach (comprising ultrasonic, calendering, and vacuum centrifugal mixing), single‐ and multi‐walled functionalized CNTs (FCNTs) were incorporated into two foam composites containing various commercially available microballoon grades (S38HS, S60HS, and H50 from 3M). The FCNT‐reinforced composites were tested for compressive strength and apparent shear strength before and after hot/wet conditioning. The results showed that the FCNT‐reinforced composites' mechanical properties depended on the vacuum pressure used during processing. Compared with pristine and commercially available syntactic foam (EC‐3500 from 3M), the FCNT‐reinforced composites processed at high vacuum (0.2 kPa) showed significant increase in compressive strength and apparent shear strength before and after hot/wet conditioning. Dynamic mechanical analysis showed an increase of about 22°C in glass transition temperature for composites processed at high vacuum with 0.5 wt % FCNT and 45 wt % S38HS–5 wt % S60HS microballoons. Thermogravimetric analysis indicated water absorption and lower decomposition temperature for the FCNT‐reinforced composite mixed at atmospheric pressure, whereas no significant change was observed for the compound processed at high vacuum. Fracture analysis showed matrix failure for the composite processed at high vacuum and microballoon crushing for the composite mixed at atmospheric pressure. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

ACE2, the Receptor that Enables Infection by SARS-CoV-2: Biochemistry,Structure, Allostery and Evaluation of the Potential Development of ACE2 Modulators

Angiotensin converting enzyme 2 (ACE2) is the human receptor that interacts with the spike protein of coronaviruses, including the one that produced the 2020 coronavirus pandemic (COVID-19). Thus, ACE2 is a potential target for drugs that disrupt the interaction of human cells with SARS-CoV-2 to abolish infection. There is also interest in drugs that inhibit or activate ACE2, that is, for cardiovascular disorders or colitis. Compounds binding at alternative sites could allosterically affect the interaction with the spike protein. Herein, we review biochemical, chemical biology, and structural information on ACE2, including the recent cryoEM structures of full-length ACE2. We conclude that ACE2 is very dynamic and that allosteric drugs could be developed to target ACE2. At the time of the 2020 pandemic, we suggest that available ACE2 inhibitors or activators in advanced development should be tested for their ability to allosterically displace the interaction between ACE2 and the spike protein.     

Interleukin-1β Modulation of the Mechanobiology of Primary Human Pulmonary Fibroblasts: Potential Implications in Lung Repair

Pro-inflammatory cytokines like interleukin-1β (IL-1β) are upregulated during early responses to tissue damage and are expected to transiently compromise the mechanical microenvironment. Fibroblasts are key regulators of tissue mechanics in the lungs and other organs. However, the effects of IL-1β on fibroblast mechanics and functions remain unclear. Here we treated human pulmonary fibroblasts from control donors with IL-1β and used Atomic Force Microscopy to unveil that IL-1β significantly reduces the stiffness of fibroblasts concomitantly with a downregulation of filamentous actin (F-actin) and alpha-smooth muscle (α-SMA). Likewise, COL1A1 mRNA was reduced, whereas that of collagenases MMP1 and MMP2 were upregulated, favoring a reduction of type-I collagen. These mechanobiology changes were functionally associated with reduced proliferation and enhanced migration upon IL-1β stimulation, which could facilitate lung repair by drawing fibroblasts to sites of tissue damage. Our observations reveal that IL-1β may reduce local tissue rigidity by acting both intracellularly and extracellularly through the downregulation of fibroblast contractility and type I collagen deposition, respectively. These IL-1β-dependent mechanical effects may enhance lung repair further by locally increasing pulmonary tissue compliance to preserve normal lung distension and function. Moreover, our results support that IL-1β provides innate anti-fibrotic protection that may be relevant during the early stages of lung repair.     

The Impact of [C16Pyr][Amp] on the Aggressiveness in Breast and Prostate Cancer Cell Lines

Breast (BrCa) and prostate (PCa) cancers are the most common malignancies in women and men, respectively. The available therapeutic options for these tumors are still not curative and have severe side effects. Therefore, there is an urgent need for more effective antineoplastic agents. Herein, BrCa, PCa, and benign cell lines were treated with two ionic liquids and two quinoxalines and functional experiments were performed—namely cell viability, apoptosis, cytotoxicity, and colony formation assays. At the molecular level, an array of gene expressions encompassing several molecular pathways were used to explore the impact of treatment on gene expression. Although both quinoxalines and the ionic liquid [C2OHMIM][Amp] did not show any effect on the BrCa and PCa cell lines, [C16Pyr][Amp] significantly decreased cell viability and colony formation ability, while it increased the apoptosis levels of all cell lines. Importantly, [C16Pyr][Amp] was found to be more selective for cancer cells and less toxic than cisplatin. At the molecular level, this ionic liquid was also associated with reduced expression levels of CPT2, LDHA, MCM2, and SKP2, in both BrCa and PCa cell lines. Hence, [C16Pyr][Amp] was shown to be a promising anticancer therapeutic agent for BrCa and PCa cell lines.     

Effect of rheology and humic acids on the transport of environmental fluids: Potential implications for soil remediation revealed through microfluidics

This study investigated the potential effect of shear rheology and humic acids (HA) on the subsurface transport of polymeric fluids used for the remediation of contaminants. Polymeric fluids were prepared with guar, scleroglucan, and carboxymethyl cellulose (CMC). Guar fluids can be used to suspend reactive particles for contaminant degradation. Fluids prepared with 2.5 g/L of guar in water were viscous, and the crosslinker borax (1 g/L) made them viscoelastic. Microfluidics experiments showed that the increase in elasticity blocked the flow of guar in 350 μm channels. Guar, CMC, or scleroglucan fluids containing sodium thiosulfate can be used to trap toxic Cr(VI) in the subsurface and reduce it to harmless Cr(III). Trapping of Cr(VI) is achieved by the gelation of the fluids upon contact with chromium. Before mixing with chromium, HA did not affect the flow of CMC, guar, and scleroglucan in microfluidic channels. Quartz-crystal microbalance with dissipation monitoring experiments indicates that HA reduced sorption of guar onto silica, potentially promoting the transport of guar fluids in sandy aquifers. While HA slightly decreased the rate of gelation of CMC and scleroglucan upon contact with chromium, it did not affect the fast gelation rate of guar. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48465.     

Molecular dynamics simulations and experimental studies of the thermomechanical response of an epoxy thermoset polymer

We report a detailed comparison between molecular dynamics predictions and experimental results for a wide range of thermo-mechanical properties of an epoxy resin system: diglycidyl ether of bisphenol A (DGEBA) cured with 3,3′ diamino-diphenyl sulfone (33DDS). A set of carefully designed and characterized experiments provides validation data for the simulations that predict the molecular structure and properties of the thermoset. Our results show that current state-of-the-art molecular dynamics simulations provide quantitative predictions for this epoxy system in its glassy state, including elastic moduli, coefficient of thermal expansion and specific heat. The glass transition temperature is also accurately predicted once a correction is included to account for the difference in cooling rates between the simulations and experiments. Our results also indicate that viscoelastic and thermal properties of the thermoset polymer in its rubbery state are more challenging to predict since the effect of timescales is not well understood.     

Structural,electric modulus and complex impedance analysis of ZnO/TiO2 composite ceramics

ZnO/TiO₂ composite ceramics have been prepared by solid‐state reaction technique at 900°C. The X‐ray diffraction results revealed the formation of secondary phases referred to as spinel Zn₂TiO₄ and hexagonal ZnTiO₃. The structural analysis showed that all the composites that have been prepared have a polycrystalline nature and a hexagonal wurtzite structure. The complex modulus (M) and electric impedance of the samples have been investigated by broadband dielectric spectroscopy in a wide range of temperature (40°C‐110°C) and frequency (0.1 Hz to 10 MHz). The modulus plots (M′′, M′) illustrate the presence of non‐Debye type of relaxations attributed to the effects of interfacial and dipolar polarizations. The real and the imaginary parts of the impedance are well fitted to equivalent circuit models. At high temperatures, Z″_max varies from 0.03 × 10⁶ to 4.9 × 10⁶ Ω when the TiO₂ doping concentration increases from 1 to 7 wt%. From the obtained results, the secondary phase ZnTiO₃ plays an important role in the electrical properties.