Exploiting soft, adaptive microgels as building blocks for soft materials with controlled and predictable viscoelastic properties is of great interest for both industry and fundamental research. Here ...the flow properties of different poly(
N
-isopropylacrylamide) (pNIPAM) microgels are compared: regularly crosslinked
versus
ultra-low crosslinked (ULC) microgels. The latter are the softest microgels that can be produced
via
precipitation polymerization. The viscosity of ULC microgel suspensions at low concentrations can be described with models typically used for hard spheres and regularly crosslinked microgels. In contrast, at higher concentrations, ULC microgels show a much softer behavior compared to regularly crosslinked microgels. The increase of the storage modulus with concentration discloses that while for regularly crosslinked microgels the flow properties are mainly determined by the more crosslinked core, for ULC microgels the brush-like interaction is dominant at high packing fractions. Both the flow curves and the increase of the storage modulus with concentration indicates that ULC microgels can form glass and even reach an apparent jammed state despite their extreme softness. In contrast, the analysis of oscillatory frequency sweep measurements show that when approaching the glass transition the ultra-low crosslinked microgels behave as the regularly crosslinked microgels. This is consistent with a recent study showing that in this concentration range the equilibrium phase behavior of these ULC microgels is the one expected for regularly crosslinked microgels.
Solutions of ultra-low crosslinked microgels show viscoelastic properties in between rigid particles and flexible polymers. The dominance of particle-like and polymer-like behavior depends on the concentration of microgel in solution.
We study the rheological properties of sodium polystyrene sulfonate in salt-free and excess added salt solution. The overlap concentration scales as c* ∝ N –2 (DI water) and c* ∝ N –0.77 (excess ...salt), corresponding to rodlike and expanded coil conformations, respectively. A comparison of small-angle X-ray scattering and viscosity data reveals that c* in salt-free solution may be quantitatively estimated as the point at which the viscosity of a NaPSS solution is ≃5/3 that of the solvent. The entanglement crossover and entanglement density are found to be approximately independent of the concentration of the added salt, and similar to those of neutral polystyrene in good or θ solvents. These results indicate that polymer conformation has a weaker effect on entanglement formation in solution than expected by packing models of polymer entanglement.
Wetlands constitute the main natural source of methane on Earth due to their high content of natural organic matter (NOM), but key drivers, such as electron acceptors, supporting methanotrophic ...activities in these habitats are poorly understood. We performed anoxic incubations using freshly collected sediment, along with water samples harvested from a tropical wetland, amended with
C-methane (0.67 atm) to test the capacity of its microbial community to perform anaerobic oxidation of methane (AOM) linked to the reduction of the humic fraction of its NOM. Collected evidence demonstrates that electron-accepting functional groups (e.g., quinones) present in NOM fueled AOM by serving as a terminal electron acceptor. Indeed, while sulfate reduction was the predominant process, accounting for up to 42.5% of the AOM activities, the microbial reduction of NOM concomitantly occurred. Furthermore, enrichment of wetland sediment with external NOM provided a complementary electron-accepting capacity, of which reduction accounted for ∼100 nmol
CH
oxidized · cm
· day
Spectroscopic evidence showed that quinone moieties were heterogeneously distributed in the wetland sediment, and their reduction occurred during the course of AOM. Moreover, an enrichment derived from wetland sediments performing AOM linked to NOM reduction stoichiometrically oxidized methane coupled to the reduction of the humic analogue anthraquinone-2,6-disulfonate. Microbial populations potentially involved in AOM coupled to microbial reduction of NOM were dominated by divergent biota from putative AOM-associated archaea. We estimate that this microbial process potentially contributes to the suppression of up to 114 teragrams (Tg) of CH
· year
in coastal wetlands and more than 1,300 Tg · year
, considering the global wetland area.
The identification of key processes governing methane emissions from natural systems is of major importance considering the global warming effects triggered by this greenhouse gas. Anaerobic oxidation of methane (AOM) coupled to the microbial reduction of distinct electron acceptors plays a pivotal role in mitigating methane emissions from ecosystems. Given their high organic content, wetlands constitute the largest natural source of atmospheric methane. Nevertheless, processes controlling methane emissions in these environments are poorly understood. Here, we provide tracer analysis with
CH
and spectroscopic evidence revealing that AOM linked to the microbial reduction of redox functional groups in natural organic matter (NOM) prevails in a tropical wetland. We suggest that microbial reduction of NOM may largely contribute to the suppression of methane emissions from tropical wetlands. This is a novel avenue within the carbon cycle in which slowly decaying NOM (e.g., humic fraction) in organotrophic environments fuels AOM by serving as a terminal electron acceptor.
The human gut microbiome harbors hundreds of bacterial species with diverse biochemical capabilities. Dozens of drugs have been shown to be metabolized by single isolates from the gut microbiome, but ...the extent of this phenomenon is rarely explored in the context of microbial communities. Here, we develop a quantitative experimental framework for mapping the ability of the human gut microbiome to metabolize small molecule drugs: Microbiome-Derived Metabolism (MDM)-Screen. Included are a batch culturing system for sustained growth of subject-specific gut microbial communities, an ex vivo drug metabolism screen, and targeted and untargeted functional metagenomic screens to identify microbiome-encoded genes responsible for specific metabolic events. Our framework identifies novel drug-microbiome interactions that vary between individuals and demonstrates how the gut microbiome might be used in drug development and personalized medicine.
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•Development of subject-personalized ex vivo batch cultures of the gut microbiome•Discovery of diverse drug-microbiome interactions using MDM-Screen•MDM-Screen quantifies drug metabolism by personalized gut microbial communities•Functional genomic and metagenomic screens identify drug-metabolizing enzymes
Each human has a diverse gut microbiome, which can metabolize drugs differently. In this resource, Javdan et al. present a way to capture and grow much of the unique diversity of human microbiomes in culture and also a way to detect many of our microbiome-derived metabolites. Together, they use these unique gut communities and the metabolomics pipeline to see how personalized microbiomes metabolize drugs in different ways.
We study the entanglement properties of polyelectrolytes in salt-free and excess-salt solutions, corresponding to rod-like and expanded coil conformations, respectively. While the solvent’s ionic ...strength has a large impact on the conformation of polyelectrolytes, it does not affect its entanglement density and entanglement crossover. This contradicts current models of polymer entanglement and suggests that the density of binary contacts in solution is not affected by the solvent quality. Based on this observation, we work out the reptation dynamics of polyelectrolytes in salt-free solution, which differ appreciably from earlier models.
RATIONALE:Hypertension represents a major risk factor for stroke, myocardial infarction, and heart failure and affects 30% of the adult population. Mitochondrial dysfunction contributes to ...hypertension, but specific mechanisms are unclear. The mitochondrial deacetylase Sirt3 (Sirtuin 3) is critical in the regulation of metabolic and antioxidant functions which are associated with hypertension, and cardiovascular disease risk factors diminish Sirt3 level.
OBJECTIVE:We hypothesized that reduced Sirt3 expression contributes to vascular dysfunction in hypertension, but increased Sirt3 protects vascular function and decreases hypertension.
METHODS AND RESULTS:To test the therapeutic potential of targeting Sirt3 expression, we developed new transgenic mice with global Sirt3OX (Sirt3 overexpression), which protects from endothelial dysfunction, vascular oxidative stress, and hypertrophy and attenuates Ang II (angiotensin II) and deoxycorticosterone acetate–salt induced hypertension. Global Sirt3 depletion in Sirt3 mice results in oxidative stress due to hyperacetylation of mitochondrial superoxide dismutase (SOD2), increases HIF1α (hypoxia-inducible factor-1), reduces endothelial cadherin, stimulates vascular hypertrophy, increases vascular permeability and vascular inflammation (p65, caspase 1, VCAM vascular cell adhesion molecule-1, ICAM intercellular adhesion molecule-1, and MCP1 monocyte chemoattractant protein 1), increases inflammatory cell infiltration in the kidney, reduces telomerase expression, and accelerates vascular senescence and age-dependent hypertension; conversely, increased Sirt3 expression in Sirt3OX mice prevents these deleterious effects. The clinical relevance of Sirt3 depletion was confirmed in arterioles from human mediastinal fat in patients with essential hypertension showing a 40% decrease in vascular Sirt3, coupled with Sirt3-dependent 3-fold increases in SOD2 acetylation, NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) activity, VCAM, ICAM, and MCP1 levels in hypertensive subjects compared with normotensive subjects.
CONCLUSIONS:We suggest that Sirt3 depletion in hypertension promotes endothelial dysfunction, vascular hypertrophy, vascular inflammation, and end-organ damage. Our data support a therapeutic potential of targeting Sirt3 expression in vascular dysfunction and hypertension.
We report viscosity data of nonentangled sodium polystyrene sulfonate (NaPSS) in salt-free aqueous solution as a function of polymer concentration (c) and degree of polymerization (N). Different ...empirical equations are examined and found not to describe the semidilute solution viscosity over a wide concentration range and/or to yield values of η that do not match dilute solution measurements. Deviations from the scaling prediction of ηsp ∝ c 1/2 (Fuoss’ law) are observed at high concentrations. Specifically, we find ηsp ≈ N 1.26 c 1/2 e1.4c in the semidilute regime, which agrees with the scaling prediction only for c ≲ 0.02 M. The viscosity data presented in this study and in earlier reports show a high degree of consistency. A comparison with diffusion measurements for NaPSS in salt-free solution by Oostwal and co-workers suggests that the disagreement between the scaling theory and experiments does not arise solely from the concentration dependence of the monomeric friction coefficient.
Polyelectrolytes are a class of polymers possessing ionic groups on their repeating units. Since counterions can dissociate from the polymer backbone, polyelectrolyte chains are strongly influenced ...by electrostatic interactions. As a result, the physical properties of polyelectrolyte solutions are significantly different from those of electrically neutral polymers. The aim of this article is to highlight key results and some outstanding questions in the polyelectrolyte research from recent literature. We focus on the influence of electrostatics on conformational and hydrodynamic properties of polyelectrolyte chains. A compilation of experimental results from the literature reveals significant disparities with theoretical predictions. We also discuss a new class of polyelectrolytes called poly(ionic liquid)s that exhibit unique physical properties in comparison to ordinary polyelectrolytes. We conclude this review by listing some key research challenges in order to fully understand the conformation and dynamics of polyelectrolytes in solutions.
We highlight key results and outstanding questions emerging from recent literature, aiming to provide readers with a comprehensive overview of the latest advancements in understanding the conformation and dynamics of polyelectrolytes in dilute solutions.
In this paper we present an alternative representation of the diffusion equation and the diffusion–advection equation using the fractional calculus approach, the spatial-time derivatives are ...approximated using the fractional definition recently introduced by Caputo and Fabrizio in the range β,γ∈(0;2 for the space and time domain respectively. In this representation two auxiliary parameters σx and σt are introduced, these parameters related to equation results in a fractal space–time geometry provide an entire new family of solutions for the diffusion processes. The numerical results showed different behaviors when compared with classical model solutions. In the range β,γ∈(0;1), the concentration exhibits the non-Markovian Lévy flights and the subdiffusion phenomena; when β=γ=1 the classical case is recovered; when β,γ∈(1;2 the concentration exhibits the Markovian Lévy flights and the superdiffusion phenomena; finally when β=γ=2 the concentration is anomalous dispersive and we found ballistic diffusion.
•Fractional calculus is applied to the diffusion and the diffusion–advection equation.•The Caputo–Fabrizio fractional derivative is applied.•The generalization of the equations in space–time exhibits anomalous behavior.•To keep the dimensionality an auxiliary parameter σ is introduced.•The numerical solutions are obtained using the numerical Laplace transform algorithm.
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Nicotinic acetylcholine receptors (nAChRs) are widely distributed throughout the central nervous system, being expressed in neurons and non-neuronal cells, where they participate in a ...variety of physiological responses like memory, learning, locomotion, attention, among others. We will focus on the α7 nAChR subtype, which has been implicated in neuroprotection, synaptic plasticity and neuronal survival, and is considered as a potential therapeutic target for several neurological diseases. Oxidative stress and neuroinflammation are currently considered as two of the most important pathological mechanisms common in neurodegenerative diseases such as Alzheimer, Parkinson or Huntington diseases. In this review, we will first analysed the distribution and expression of nAChR in mammalian brain. Then, we focused on the function of the α7 nAChR subtype in neuronal and non-neuronal cells and its role in immune responses (cholinergic anti-inflammatory pathway). Finally, we will revise the anti-inflammatory pathway promoted via α7 nAChR activation that is related to recruitment and activation of Jak2/STAT3 pathway, which on the one hand inhibits NF-κB nuclear translocation, and on the other hand, activates the master regulator of oxidative stress Nrf2/HO-1. This review provides a profound insight into the role of the α7 nAChR subtype in microglia and point out to microglial α7/HO-1 pathway as an anti-inflammatory therapeutic target.
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