- Insights into the thermal and chemical stability of multilayered V2CTx MXene. [Journal Article]
- NNanoscale 2019 May 23
- We report on the thermal stability of multilayered V2CTx MXenes under different atmospheres by combining in situ Raman spectroscopy with ex situ X-ray diffraction (XRD), X-ray photoelectron spectrosc…
We report on the thermal stability of multilayered V2CTx MXenes under different atmospheres by combining in situ Raman spectroscopy with ex situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) in order to elucidate and monitor the molecular, electronic, and structural changes of both the surface and bulk of the V2CTx MXene which has recently received much attention. The MXene samples were heated up to 600 °C in inert (N2), oxidative (CO2, air), and reductive (H2) environments under similar conditions. In situ Raman showed that the V[double bond, length as m-dash]O vibration for two-dimensional vanadia is preserved up to 600 °C under N2, while its intensity reduces under H2. When heated above 300 °C under either CO2 or air, V2CTx slightly oxidizes or transforms into V2O5, respectively. Furthermore, SEM revealed the presence of an accordion-like layered structure for the MXene under N2 and H2, while under CO2 and air the layered structure collapses and forms VO2 (V4+) and V2O5 (V5+) crystals, respectively. XPS reveals that, regardless of the gas, surface V species oxidize above 300 °C during the dehydration process. Finally, we demonstrated that the partial dehydration of V2CTx results in the partial oxidation of the material, and the total dehydration is achieved once 700 °C is reached. We believe that our methodology is a unique alternative to tune the dehydration, oxidation, and properties of V2CTx, which allows for the expansion of applications of MXenes.
- Direct Observation of Primary C-H Bond Oxidation by An Oxido-iron(IV) Porphyrin π-Radical Cation Complex in a Fluorinated Carbon Solvent. [Journal Article]
- ACAngew Chem Int Ed Engl 2019 May 22
- Oxido-iron(IV) porphyrin π-radical cation species are involved in a variety of heme-containing enzymes, which has been attracting considerable attentions due to its biological importance and characte…
Oxido-iron(IV) porphyrin π-radical cation species are involved in a variety of heme-containing enzymes, which has been attracting considerable attentions due to its biological importance and characteristic oxidation states consisting of the high-valent iron center and the π-conjugated macrocyclic ligand. However, the short lifetime of the complex due to its high reactivity has hampered detailed reactivity study. We herein report remarkable lifetime elongation (80 s at 10 °C) of FeIV(TMP+•)(O)(Cl) (TMP: 5,10,15,20-tetramesitylporphyrin dianion) (2) produced by the oxidation of FeIII(TMP)(Cl) (1) by ozone in α,α,α-trifluorotoluene (TFT), which is 720 times longer lifetime as compared to that of the currently most stable one reported by Groves et al. (J. Am. Chem. Soc. 2009, 131, 9640-9641). The drastic elongation of the lifetime improves reaction efficiency of 2 toward inert alkane substrates, and allows us to observe the reaction of 2 with a primary C-H bond (BDEC-H = ca. 100 kcal mol-1) directly. We also succeeded to obtain activation parameters for cyclohexane hydroxylation.
- Understanding the Impact of Relative Humidity and Coexisting Soluble Iron on the OH-Initiated Heterogeneous Oxidation of Organophosphate Flame Retardants. [Journal Article]
- ESEnviron Sci Technol 2019 May 22
- The current uncertainties in the reactivity and atmospheric persistence of particle-associated chemicals present a challenge for the prediction of long-range transport and deposition of emerging chem…
The current uncertainties in the reactivity and atmospheric persistence of particle-associated chemicals present a challenge for the prediction of long-range transport and deposition of emerging chemicals such as organophosphate flame retardants, which are ubiquitous in the global environment. Here, the OH-initiated heterogeneous oxidation kinetics of organophosphate flame retardants (OPFRs) coated on inert (NH4)2SO4 and redox-active FeSO4 particles were systematically determined as a function of relative humidity (RH). The derived reaction rate constants for the heterogeneous loss of tricresyl phosphate (TCP; k,TCP) and tris(2-butoxyethyl) phosphate (TBEP; k,TBEP) were in the range of (2.69-3.57)×10-12 and (3.06-5.55)×10-12 cm3 molecules-1 s-1 respectively, depending on the RH and coexisting Fe(II) content. The k,TCP (coated on (NH4)2SO4) was relatively constant over the investigated RH range while k,TBEP was enhanced by up to 19% with increasing RH. For both OPFRs, the presence of Fe(II) enhanced their k by up to 53% over inert (NH4)2SO4. These enhancement effects (RH and Fe(II)) were attributed to fundamental changes in the organic phase state (higher RH lowered particle viscosity) and Fenton-type chemistry which resulted in the formation of reactive oxygen species, respectively. Such findings serve to emphasize the importance of ambient RH, the phase state of particle-bound organics in general, and the presence of coexisting metallic species, for an accurate description of the degradation kinetics and aging of particulate OPFRs in models used to evaluate their atmospheric persistence.
- Photochemical Transformations of Dichloroacetamide Safeners. [Journal Article]
- ESEnviron Sci Technol 2019 May 22
- Dichloroacetamide safeners are commonly added to commercial chloroacetamide herbicide formulations and widely used worldwide, but their environmental fate has garnered little scrutiny due to their cl…
Dichloroacetamide safeners are commonly added to commercial chloroacetamide herbicide formulations and widely used worldwide, but their environmental fate has garnered little scrutiny due to their classification as "inert" ingredients. Here, we investigated the photolysis of dichloroacetamide safeners to better understand their persistence and the nature of their transformation products in surface waters. High-resolution mass spectrometry (HRMS) and nuclear magnetic resonance spectroscopy (NMR) were used to characterize photoproducts. Of the four commonly used dichloroacetamide safeners, only benoxacor undergoes direct photolysis under simulated natural sunlight (t1/2 = ~ 10 min). Via a photo-initiated ring closure, benoxacor initially yields a monochlorinated intermediate that degrades over longer irradiation timescales to produce two fully dechlorinated diastereomers and a tautomer, which further photodegrade over several days to a structurally-related aldehyde confirmed via NMR. Dichlormid, AD-67, and furilazole were more slowly degraded by indirect photolysis in the presence of the photosensitizers nitrate, nitrite, and humic acid. Reactive entities involved in these reactions are likely hydroxyl radical and singlet oxygen based upon the use of selective quenchers. These safeners also directly photolyzed under higher energy UV light, suggesting their potential transformation in engineered systems using UV for disinfection. That dichloroacetamide safeners can undergo photolysis in environmental systems over relevant timescales demonstrates the importance of evaluating the fate of this class of "inert" agrochemicals.
- Tumor-targeting immune system engagers (ISErs) activate human neutrophils after binding to cancer cells. [Journal Article]
- BBiochemistry 2019 May 22
- Immune System Engagers (ISErs) are a new class of immunotherapeutics against cancer. They comprise two or more tumor-targeting peptides and an immune-stimulating effector peptide connected by inert p…
Immune System Engagers (ISErs) are a new class of immunotherapeutics against cancer. They comprise two or more tumor-targeting peptides and an immune-stimulating effector peptide connected by inert polymer linkers. They are produced by solid phase peptide synthesis and share the specific targeting activities of antibodies (IgGs) but are much smaller in size and exploit a different immune stimulating mechanism. Two ISErs (Y-9 and Y-59) that bind to the cancer cell markers integrin α3 and EphA2, respectively, are analyzed here with respect to their immune cell stimulation. We have previously shown that they activate formyl peptide receptors on myeloid immune cells, induce respiratory burst in neutrophils and myeloid chemotaxis in solution. It remained, however, unclear whether these molecules can stimulate immune cells while bound to tumor cells, an essential step in the hypothesized mode of action. Here we demonstrate that ISEr Y-9 induced respiratory burst and caused a shape change of neutrophils when bound to the surface of protein A beads as a model of tumor cells. More importantly, tumor cell lines carrying receptor-bound Y-9 or Y-59 also activated neutrophils, evidenced by a significant shape change. Interestingly, similar activation was induced by the supernatants of the ISEr incubated cells, indicating that ISErs released from tumor cells, intact or degraded into fragments, significantly contributed to the immune stimulation. These findings provide new evidence for the mode of action of ISErs, namely by targeting cancer cells and subsequently provoking an innate immune response against them.
- Biofilm Formation by Listeria monocytogenes Utilizes a Primary Colonizing Microorganism in Flowing Systems. [Journal Article]
- JFJ Food Prot 1993; 56(12):1022-1028
- Listeria monocytogenes serotype 3a and Pseudomonas fragi ATCC 4973 were examined for attachment capability and biofilm development on glass coverslips under flowing systems. Tryptic soy broth supplem…
Listeria monocytogenes serotype 3a and Pseudomonas fragi ATCC 4973 were examined for attachment capability and biofilm development on glass coverslips under flowing systems. Tryptic soy broth supplemented with yeast extract was the growth medium. A continuous flow slide chamber was developed for in situ observations using phase-contrast microscopy. Glass coverslips were examined by epifluorescent and scanning electron microscopy for biofilm formation. The ultrastructure of attached test organisms was examined for the presence of exopolymers using transmission electron microscopy. In pure cultures, attachment of L. monocytogenes to glass coverslips was sparse, while P. fragi accumulated on glass coverslips as a confluent layer of cells. When L. monocytogenes was grown in mixed culture with P. fragi , an exopolymer-producing microorganism, attachment and microcolony formation by L. monocytogenes was enhanced. Results suggest that under flowing conditions the presence of an exopolymer-producing microorganism may be more important than hydrophobicity, surface charge, or flagellar movement in attachment of L. monocytogenes to inert surfaces.
- Improving the Osteogenicity of PCL Fiber Substrates by Surface-Immobilization of Bone Morphogenic Protein-2. [Journal Article]
- ABAnn Biomed Eng 2019 May 21
- Polycaprolactone (PCL) fiber scaffolds are attractive, albeit inert, substrates for ligament regeneration, that may be improved by incorporating trophic factors to guide tissue remodeling in vivo. In…
Polycaprolactone (PCL) fiber scaffolds are attractive, albeit inert, substrates for ligament regeneration, that may be improved by incorporating trophic factors to guide tissue remodeling in vivo. In particular, immobilization of bone morphogenic protein-2 (BMP-2) to the scaffold surface may facilitate rapid and robust integration of the scaffold with adjacent bone tissues. As a first step toward testing this, model PCL surfaces were modified by the addition of heparin (Hep) and BMP-2 to facilitate osteoblastic differentiation. Specifically, Hep was combined with PCL at 0, 0.5, and 1 wt% (denoted as PCL, PCL-0.5Hep, and PCL-1Hep), cast into films, and then BMP-2 was immobilized to surfaces by either adsorption and covalent conjugation. Here, BMP-2 concentration increased systematically with incorporation of Hep, and higher concentrations were achieved by covalent conjugation. Next, blends were electrospun to form thin meshes with fiber diameters of 0.92, 0.62, and 0.54 μm for PCL, PCL-0.5Hep, and PCL-1Hep, respectively. Mesenchymal stem cells (MSCs) had no difficulty attaching to and proliferating on all meshes. Lastly, PCL-1Hep meshes were prepared with adsorbed or covalently conjugated BMP-2 and cultured with MSCs in the absence of osteogenic factors. Under these conditions, alkaline phosphatase activity and deposition of bone sialoprotein, osteopontin, and calcium minerals-markers of osteoblastic differentiation-were significantly higher on surfaces with immobilized BMP-2. Together, these data indicate that covalent immobilization of trophic factors confers bioactivity to scaffolds, which may be applied in a spatially controlled manner for ligament regeneration and bone integration.
- Taguchi's methods to optimize the properties and bioactivity of 3D printed polycaprolactone/mineral trioxide aggregate scaffold: Theoretical predictions and experimental validation. [Journal Article]
- JBJ Biomed Mater Res B Appl Biomater 2019 May 21
- Mineral trioxide aggregate (MTA) can provide bioactivity to poly-caprolactone (PCL), which is an inert polymer used to print scaffolds. However, testing all combinations of scaffold characteristics (…
Mineral trioxide aggregate (MTA) can provide bioactivity to poly-caprolactone (PCL), which is an inert polymer used to print scaffolds. However, testing all combinations of scaffold characteristics (e.g., composition, pore size, and distribution) to optimize properties of scaffolds is time-consuming and costly. The Taguchi's methods can identify characteristics that have major influences on the properties of complex designs, hence decreasing the number of combinations to be tested. The objective was to assess the potential of Taguchi's methods as a predictive tool for the optimization of bioactive scaffold printed using electro-hydro dynamic jetting. A three-level approach assessed the influence of PCL/MTA proportion, pore size, fiber dimension and number of layers in pH, degradation rate, porosity, yield strength, and Young's modulus. Data were analyzed using Tukey's honest significant difference test, analysis of mean and signal-to-noise ratio (S/N) test. Cytocompatibility and differentiation potential were assessed for 5 and 30 days using dental pulp stem cells and analyzed with one-way analysis of variance (proliferation) or Mann-Whitney (qPCR). The S/N ratio and analysis of mean showed that fiber diameter and composition were the most influential characteristics in all properties. The experimental data confirmed that the addition of MTA to PCL increased the pH and scaffold degradation. Only PCL and PCL with 4% MTA allowed cell proliferation. The latter increased the genetic expression of ALP, COL-1, OCN, and MSX-1. The theoretical predictions were confirmed by the experiments. The Taguchi's identified the inputs that can be disregarded to optimize 3D printed meshed bioactive scaffolds.
- Adverse Events and Nocebo Effects in Inflammatory Bowel Disease: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. [Journal Article]
- JCJ Crohns Colitis 2019 May 03
- CONCLUSIONS: AEs are commonly reported by patients randomized to either placebo or active treatment in IBD RCTs. Clinically relevant differences in AE, SAE, and AE-related withdrawal were not observed.
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- Manganese(iii)-chelated porphyrin microbubbles for enhanced ultrasound/MR bimodal tumor imaging through ultrasound-mediated micro-to-nano conversion. [Journal Article]
- NNanoscale 2019 May 21
- Manganese(iii)-chelated porphyrin microbubbles (MnP-MBs) were fabricated by self-assembly from a Mn-chelated porphyrin lipid followed by encapsulating perfluoropropane-an inert gas. The obtained MnP-…
Manganese(iii)-chelated porphyrin microbubbles (MnP-MBs) were fabricated by self-assembly from a Mn-chelated porphyrin lipid followed by encapsulating perfluoropropane-an inert gas. The obtained MnP-MBs exhibited enhanced ultrasound imaging ability after intravenous injection. Under the guidance of ultrasound imaging, MnP-MBs could be converted into nanoparticles in situ with local tumor ultrasound disruption, achieving rapid tumor MRI contrast enhancement within 30 min at a very low Mn injection dose of 0.09 mg (1.65 μmol) per kg.