Rate-limiting Processes Research Articles

In-Situ Electrochemical Impedance Spectroscopy for Characterizing Transport Response during Material Irradiation

Radiation-induced crystalline disorder in complex oxides has a significant effect on the mass transport properties, namely the conductivity of the material. In the case of Gd2Ti2O7 (GTO) we observed that with increasing disorder, the conductivity of GTO subsequently increases. However, in the case of materials such as Yttria Stabilized Zirconia (YSZ), we observe a high radiation-tolerance to disorder and amorphization. Furthermore, the conductivity measured post-irradiation is comparable to the pristine state conductivity of YSZ. In theory, we might not see the permanent change in conductivity due to the inherent self-annealing propensity of YSZ. Such high rates of defect recombination may be masking any transport changes in the materials only present during the irradiation process. Thus, to elucidate these mass transport properties only present during irradiation we are developing an in-situ electrochemical impedance spectroscopy (EIS) method capable of experimentally probing the materials while they are undergoing irradiation.With this novel in-situ EIS method we can extract information that would otherwise be missed in the standard ex-situ EIS characterization methods. Information such as: 1) rate of increase of conductivity between the onset of irradiation until steady state is reached, 2) the magnitude of such conductivity changes under irradiation at steady state, 3) the rate of decrease of conductivity once the beam is turned off until conductivity reaches a post-irradiation steady state. Although this is especially significant for materials that are radiation resistant, extracting the rate of increase of conductivity is also relevant and interesting for materials that are not as radiation resistant such as with GTO.EIS is the preferred method for monitoring the electrical properties over other techniques such as with DC signals, because with the sinusoidal signals applied in EIS we extract these time-scale properties which make it possible to separate transport resistances from other rate-limiting processes. For the development of in-situ EIS: conductivity pathways, electrode geometries, beam path to the material, operating parameters of the potentiostat, and other considerations were made. Preliminary results for YSZ show that in the relatively lower operating temperature of 300 °C (far below the optimal temperature for high conductivity) the conductivity significantly increases when the irradiation beam is turned on, and quickly reverts to initial conductivity levels when the beam is turned off. Major contributions to the conductivity changes are attributed to the point defects created during the irradiation process. Thermal contributions of the beamline are excluded as the major contributor when comparing the temperature expected to reach the magnitude of conductivity change as well as the rate of decrease when the initial state of YSZ conductivity is recovered. Figure 1. A) Electrode design used in preliminary experiments. B) Embedded electrode design for controlled area for more accurate conductivity calculations. C) Array of electrode geometries to optimize fabrication of embedded electrodes. D) Generalized example of ex-situ conductivity data. E) Generalized example of in-situ conductivity data. Figure 1

Determining the rate-limiting processes for cell division in Escherichia coli

A critical cell cycle checkpoint for most bacteria is the onset of constriction when the septal peptidoglycan synthesis starts. According to the current understanding, the arrival of FtsN to midcell triggers this checkpoint in Escherichia coli. Recent structural and in vitro data suggests that recruitment of FtsN to the Z-ring leads to a conformational switch in actin-like FtsA, which links FtsZ protofilaments to the cell membrane and acts as a hub for the late divisome proteins. Here, we investigate this putative pathway using in vivo measurements and stochastic cell cycle modeling at moderately fast growth rates. Quantitatively upregulating protein concentrations and determining the resulting division timings shows that FtsN and FtsA numbers are not rate-limiting for the division in E. coli. However, at higher overexpression levels, they affect divisions: FtsN by accelerating and FtsA by inhibiting them. At the same time, we find that the FtsZ numbers in the cell are one of the rate-limiting factors for cell divisions in E. coli. Altogether, these findings suggest that instead of FtsN, accumulation of FtsZ in the Z-ring is one of the main drivers of the onset of constriction in E. coli at faster growth rates.

Deletions Rate-Limit Breast and Ovarian Cancer Initiation.

Optimizing prevention and early detection of cancer requires understanding the number, types and timing of driver mutations. To quantify this, we exploited the elevated cancer incidence and mutation rates in germline BRCA1 and BRCA2 (gBRCA1/2) carriers. Using novel statistical models, we identify genomic deletions as the likely rate-limiting mutational processes, with 1-3 deletions required to initiate breast and ovarian tumors. gBRCA1/2-driven hereditary and sporadic tumors undergo convergent evolution to develop a similar set of driver deletions, and deletions explain the elevated cancer risk of gBRCA1/2-carriers. Orthogonal mutation timing analysis identifies deletions of chromosome 17 and 13q as early, recurrent events. Single-cell analyses confirmed deletion rate differences in gBRCA1/2 vs. non-carrier tumors as well as cells engineered to harbor gBRCA1/2. The centrality of deletion-associated chromosomal instability to tumorigenesis shapes interpretation of the somatic evolution of non-malignant tissue and guides strategies for precision prevention and early detection.

On the rate-limiting dynamics of force development in muscle.

Skeletal muscles produce forces relatively slowly compared with the action potentials that excite them. The dynamics of force production are governed by multiple processes, such as calcium activation, cycling of cross-bridges between myofilaments, and contraction against elastic tissues and the body. These processes have been included piecemeal in some muscle models, but not integrated to reveal which are the most rate limiting. We therefore examined their integrative contributions to force development in two conventional types of muscle models: Hill-type and cross-bridge. We found that no combination of these processes can self-consistently reproduce classic data such as twitch and tetanus. Rather, additional dynamics are needed following calcium activation and facilitating cross-bridge cycling, such as for cooperative myofilament interaction and reconfiguration. We provisionally lump such processes into a simple first-order model of 'force facilitation dynamics' that integrate into a cross-bridge-type muscle model. The proposed model self-consistently reproduces force development for a range of excitations including twitch and tetanus and electromyography-to-force curves. The model's step response reveals relatively small timing contributions of calcium activation (3%), cross-bridge cycling (3%) and contraction (27%) to overall force development of human quadriceps, with the remainder (67%) explained by force facilitation. The same set of model parameters predicts the change in force magnitude (gain) and timing (phase delay) as a function of excitatory firing rate, or as a function of cyclic contraction frequency. Although experiments are necessary to reveal the dynamics of muscle, integrative models are useful for identifying the main rate-limiting processes.

Revisit the role of hydroxylamine in sulfur-driven autotrophic denitrification

Through dedicated batch tests using the enriched sludge dominated by sulfur-oxidizing bacteria (SOB), the potential transformation of hydroxylamine (NH2OH) by SOB and the effects of NH2OH on the rate-limiting sequential reduction processes of sulfur-driven autotrophic denitrification (SDAD) were systematically explored in this study. The results indicated that NH2OH might be first converted to NO by SOB and then participate in the SDAD process, thus accelerating the utilization of S2- and contributing to the formation of N2O. Up to 3.5 mg-N/L NH2OH didn't affect the NO3- or NO2- reduction of SDAD, during which no significant changes were observed for the NH2OH concentration. Comparatively, even though NH2OH had no direct impact on the N2O reduction of SDAD, it could be consumed and therefore affect the depletion of N2O indirectly by regulating the toxic effect and electron supply of S2-. These findings provide novel implications for applying NH2OH to SDAD-based integrated processes for biological nitrogen removal.

Assessing Nonlinear Polarization in Electrochemical Cells Using AC Impedance Spectroscopy

Electrochemical energy storage and conversion devices are used to power a range of electrical loads including portable electronics, electric vehicles, and utility grids. The energy efficiency of these systems decreases with increasing current load due to energy losses (in the form of heat) associated with different processes. Electrochemical impedance spectroscopy (EIS) is a nondestructive technique commonly used to assess rate-limiting steps in electrochemical devices. Most EIS measurements for energy storage devices are only performed around open-circuit and do not probe system behavior under non-zero biases where these devices operate. Despite its widespread use, this approach does not provide information about the relative overpotentials associated with coupled nonlinear processes (e.g., diffusion limited redox reactions) commonly encountered in these systems. Furthermore, ambiguous terms such as equivalent series resistance and interfacial resistance can lead to confusion and data misinterpretation. For example, Ohm’s law cannot be applied to calculate nonlinear overpotentials using a resistance that was measured from a locally linear response.To determine overpotentials in nonlinear systems using EIS, one must integrate the individual resistive elements of the equivalent circuit as a function of steady state current. Recent experimental work has used this method to decouple ohmic, kinetic, and transport overpotentials in redox flow batteries. In these prior studies, impedance elements were derived, but analytical expressions for the corresponding overpotentials were not presented.While integrated resistance measurements are a powerful experimental tool, a more rigorous mathematical framework describing the approach is needed. The present work bridges this gap by: (i) deriving a general impedance expression for coupled charge transfer and diffusion processes and (ii) integrating the individual resistive elements as a function of steady-state current to obtain global polarization relationships. Analytical expressions for diffusion overpotentials are obtained for special cases, and numerical methods are applied when closed-form expressions do not exist. The work considers three model electrode geometries (planar, cylindrical, and spherical) and two diffusion boundary types (reflective and transmission). Finally, this treatment is extended to macroscopically homogenous porous electrodes which are relevant for describing practical devices.This presentation will highlight how measuring impedance at different steady-state biases provides critical insights on the rate-limiting processes in energy storage devices. While this work focuses on a simple Faradaic charge transfer process, the method can be used to evaluate other nonlinear phenomena in electrochemical power supplies. For example, the resistance of passive films (e.g., solid electrolyte interphase layer) in Li-ion batteries is typically only probed near open-circuit. Similarly, literature on solid-state batteries commonly uses ambiguous terms such as interfacial resistance to describe rate-limiting processes. For these more complex systems, integrating the resistive elements can provide insights on how these phenomena influence device efficiency. Overall, combining these experimental observations with physical models derived using the approach illustrated herein represents a powerful tool to guide component/system design and improve device performance. Acknowledgements This research was conducted at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE). This work is sponsored by the U.S. Department of Energy in the Office of Electricity through the Energy Storage Research Program and the Office of Energy Efficiency and Renewable Energy (EERE) in the Vehicle Technologies Office (VTO) through the Advanced Battery Materials Research (BMR) Program.

Molecular Autonomous Pathfinder Using Deep Reinforcement Learning.

Diffusion in solids is a slow process that dictates rate-limiting processes in key chemical reactions. Unlike crystalline solids that offer well-defined diffusion pathways, the lack of similar structural motifs in amorphous or glassy materials poses great challenges in bridging the slow diffusion process and material failures. To tackle this problem, we propose an AI-guided long-term atomistic simulation approach: molecular autonomous pathfinder (MAP) framework based on deep reinforcement learning (DRL), where the RL agent is trained to uncover energy efficient diffusion pathways. We employ a Deep Q-Network architecture with distributed prioritized replay buffer, enabling fully online agent training with accelerated experience sampling by an ensemble of asynchronous agents. After training, the agents provide atomistic configurations of diffusion pathways with their energy profile. We use a piecewise nudged elastic band to refine the energy profile of the obtained pathway and the corresponding diffusion time on the basis of transition-state theory. With the MAP framework, we demonstrate atomistic diffusion mechanisms in amorphous silica with time scales comparable to experiments.

Facet-Dependent Oxygen Evolution Reaction Activity of IrO2 from Quantum Mechanics and Experiments.

The diversity of chemical environments present on unique crystallographic facets can drive dramatic differences in catalytic activity and the reaction mechanism. By coupling experimental investigations of five different IrO2 facets and theory, we characterize the detailed elemental steps of the surface redox processes and the rate-limiting processes for the oxygen evolution reaction (OER). The predicted complex evolution of surface adsorbates and the associated charge transfer as a function of applied potential matches well with the distinct redox features observed experimentally for the five facets. Our microkinetic model from grand canonical quantum mechanics (GC-QM) calculations demonstrates mechanistic differences between nucleophilic attack and O-O coupling across facets, providing the rates as a function of applied potential. These GC-QM calculations explain the higher OER activity observed on the (100), (001), and (110) facets and the lower activity observed for the (101) and (111) facets. This combined study with theory and experiment brings new insights into the structural features that either promote or hinder the OER activity of IrO2, which are expected to provide parallels in structural effects on other oxide surfaces.

Modification of the endoplasmic reticulum morphology enables improved recombinant antibody expression in Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae is a versatile cell factory used for manufacturing of a wide range of products, among them recombinant proteins. Protein folding is one of the rate-limiting processes and this shortcoming is often overcome by the expression of folding catalysts and chaperones in the endoplasmic reticulum (ER). In this work, we aimed to establish the impact of ER structure on cellular productivity. The reticulon proteins Rtn1p and Rtn2p, and Yop1p are membrane curvature inducing proteins that define the morphology of the ER and depletion of these proteins creates yeast cells with a higher ER sheet-to-tubule ratio. We created yeast strains with different combinations of deletions of Rtn1p, Rtn2p, and Yop1p coding genes in cells with a normal or expanded ER lumen. We identified strains that reached up to 2.2-fold higher antibody titres compared to the control strain. The expanded ER membrane reached by deletion of the lipid biosynthesis repressor OPI1 was essential for the increased productivity. The improved specific productivity was accompanied by an up to 2-fold enlarged ER surface area and a 1.5-fold increased cross-sectional cell area. Furthermore, the strains with enlarged ER displayed an attenuated unfolded protein response. These results underline the impact that ER structures have on productivity and support the notion that reprogramming subcellular structures belongs into the toolbox of synthetic biology.

Rate-limiting mechanism of all-solid-state battery unravelled by low-temperature test-analysis flow

All-solid-state batteries (ASSBs) with potentially improved energy density and safety have been recognized as the next-generation energy storage technology. However, their performances at subzero temperatures are rarely investigated, with rate-limiting process/mechanisms unidentified. Herein, the rate-limiting process/mechanisms for -40℃ ASSBs are accurately identified/analyzed by developing a standard test-analysis flow model. We reveal that the rate-limiting processes of LiCoO2 (LCO)+sulfide solid electrolyte (SE) composite cathode are the sluggish ion transport across unfavorable interfacial reaction layer and charge transfer at damaged LCO cathode surface. After inserting Li2ZrO3 (LZO) coating layer to suppress interfacial reactions, the rate-limiting process of LCO@LZO+sulfide SE composite cathode turns into the arduous ion transport across the interphase composed of the self-decomposition products of sulfide SE. Interestingly, by replacing sulfide SE with halide SE, LCO+halide SE composite cathode delivers fast charge transfer and the ion conduction through the thick SE separator becomes the rate-limiting process, thus enabling a superior capacity retention rate (41.4 %) at -40℃. Furthermore, the capacity retention of ASSB coupling LCO+halide SE composite cathode with Si anode can be boosted from 28.9 % to 38.6 % at -40℃ by employing superionic conductor with low activation energy. These successful identifications/modulations on rate-limiting process/mechanism and improvements on low-temperature performance demonstrate the significant role of this test-analysis flow in propelling the development of low-temperature ASSBs.

Carrier-Phase DNS of Ignition and Combustion of Iron Particles in a Turbulent Mixing Layer

Three-dimensional carrier-phase direct numerical simulations (CP-DNS) of reacting iron particle dust clouds in a turbulent mixing layer are conducted. The simulation approach considers the Eulerian transport equations for the reacting gas phase and resolves all scales of turbulence, whereas the particle boundary layers are modelled employing the Lagrangian point-particle framework for the dispersed phase. The CP-DNS employs an existing sub-model for iron particle combustion that considers the oxidation of iron to FeO and that accounts for both diffusion- and kinetically-limited combustion. At first, the particle sub-model is validated against experimental results for single iron particle combustion considering various particle diameters and ambient oxygen concentrations. Subsequently, the CP-DNS approach is employed to predict iron particle cloud ignition and combustion in a turbulent mixing layer. The upper stream of the mixing layer is initialised with cold particles in air, while the lower stream consists of hot air flowing in the opposite direction. Simulation results show that turbulent mixing induces heating, ignition and combustion of the iron particles. Significant increases in gas temperature and oxygen consumption occur mainly in regions where clusters of iron particles are formed. Over the course of the oxidation, the particles are subjected to different rate-limiting processes. While initially particle oxidation is kinetically-limited it becomes diffusion-limited for higher particle temperatures and peak particle temperatures are observed near the fully-oxidised particle state. Comparing the present non-volatile iron dust flames to general trends in volatile-containing solid fuel flames, non-vanishing particles at late simulation times and a stronger limiting effect of the local oxygen concentration on particle conversion is found for the present iron dust flames in shear-driven turbulence.

Revealing the Rate-Limiting Electrode of Lithium Batteries at High Rates and Mass Loadings

Lithium-ion batteries with superior capacities and rate performance are needed due to the soaring demands for even higher energy and power device requirements. [1-2] However, the main hurdle on achieving this predominately results from poor rate performance of the electrode, related to thermodynamic limitations and slow kinetics. To determine the rate-limiting electrochemical processes in a NMC622 vs graphite cell, a methodology based upon the galvanic intermittent titration technique, for investigating the diffusion coefficient and rate kinetics from the observed overpotential at each electrode has been developed. Variable current densities have been used to simultaneously extract the thermodynamic and kinetic properties of each electrode with increasing mass loading. Graphite is observed to reach its thermodynamic limits quicker than NMC, due to the flat plateaus and overpotentials observed from the charge transfer kinetics and mass transport. At high rates and high mass loadings, the graphite electrode is responsible for limiting both lithium-ion diffusion and reaction rates in the full cell. Slow diffusion kinetics are caused by the transport of the electrolyte in the porous electrode, which limits the availability of lithium for reaction at the surface of the graphite. This current interrupt testing methodology is proposed as a fast single technique for comprehensively parameterizing the rate limitations observed in a full cell configuration [3].

Effect of surfactant surface and interfacial tension reduction on infiltration into hydrophobic porous media

Surfactant molecules increase the infiltration rate into hydrophobic porous media by lowering the infiltrating water's surface tension and the interfacial tension between hydrophobic surfaces and water molecules. We investigated the relative effect of these rate-limiting processes on the infiltration rate of aqueous surfactant solution into hydrophobic porous media. Two surfactants at various concentrations were applied at a constant pressure head to 1D columns filled with hydrophobic soil, and water was applied at the same pressure head to columns filled with surfactant-pretreated hydrophobic soil. Based on the measured contact angle, surfactant pretreatment significantly reduced the hydrophobic soil's interfacial surface tension, which increased the infiltration rate compared to the direct aqueous surfactant application to the hydrophobic soil. The latter's slower infiltration rate was attributed to the depletion of surfactant molecules due to its adsorption to the hydrophobic molecules near the advancing wetting front, yielding an increase in the surface tension of the infiltrating solution. Surfactant pretreatment increased the opportunity time for surfactant adsorption to the hydrophobic molecules, resulting in interfacial tension reduction and infiltration rate increase. Diffusion-limited surfactant adsorption on the hydrophobic surfaces, leading to reduced interfacial tension between the surface and infiltrating liquid, had a greater impact on limiting infiltration into hydrophobic porous media compared to the reduction in surface tension of the infiltrating liquid due to surfactant presence.

Plasticity of solid solution Al-Mn and Al-Mn-Si alloys

The influence of Mn and Si on the mechanical properties of solid solution Al-Mn and Al-Mn-Si alloys have been studied at 4 K, 78 K, and 298 K. The solute strengthening potency of the yield strength increases with decreasing temperature. The addition of Si stimulates the precipitation of Mn-containing dispersoids and decreases the solubility of Mn in the Al matrix, reducing the strengthening effect. The alloys exhibit Stage III of declining work hardening rate with the flow stress during the plastic flow at three temperatures. The mean slip length Λ in the work hardening model of Nabarro, Basinski, and Holt (NBH) evaluated from σΘ curves correlates with the scale of the microstructure. The strain rate sensitivity (SRS) measurements conducted at 78 K show positive SRS of Al and the alloys. At 298 K, one observes a change in SRS due to the change of the mechanism from solute-dislocation to dislocation-dislocation dominated interactions. Mn and Si decrease SRS at 298 K. Al-Mn-Si alloys exhibit negative SRS and jerk flow at a sufficiently low strain rate at 298 K. Analysis of the apparent activation volume, distance, and work has been conducted at 78 K and 298 K to understand the rate-controlling mechanisms. The results indicate that dislocation intersections are rate-limiting processes, but the atomistic mechanism of dislocation cutting varies vastly depending on the temperature and alloy composition. It is suggested that at 78 K, forest obstacles are passed by the formation of jogs and sequential activation of individual partials without making constriction to the perfect defect. At 298 K, the cutting involves constriction, the creation of jogs, and the creation of point defects at each intersection site. The calculated activation work and distance provide signatures of these processes.

A robust methodology for triple (∆47, ∆48, ∆49) clumped isotope analysis of carbonates

Analysis of ∆48 and ∆47 values of CO2 released from phosphoric acid digestion of carbonates enables the rate-limiting kinetic processes involved in carbonate mineralization to be identified and formation temperatures to be determined by accounting for these kinetic biases. This method has the benefit of only requiring analysis of a single carbonate phase. To resolve temperature from the kinetic information, mass spectrometric measurements of highest accuracy and precision are required.Here, we outline a robust methodology for high-precision triple (∆47, ∆48, ∆49) clumped isotope analysis using turbo-pumped gas and carbonate preparation lines, a common acid bath and the dual inlet of a Thermo Scientific 253plus gas source mass spectrometer, equipped with additional m/z47.5 half mass cup. By analysis of >400 replicates each, we report long-term (50 months) ∆47, CDES 90 and ∆48, CDES 90 values for three internationally accepted (ETH-1, -2 and -3) and two internal carbonate standards (GU1, Carrara) unbiased by scale compression. In order to obtain highest accuracy and precisions closest to shot noise limit it is essential to account for a sample size effect, correct raw intensities for a negative background utilizing the half mass cup, avoid pressure imbalances between sample and reference gas and distribute samples evenly across a given analytical session.We confirm ∆47, CDES 90 values that were recently assigned to ETH-1 and ETH-2. Our long-term average ∆47, CDES 90 value of 0.6032 ‰ for ETH-3, on the contrary, occurs 10 ppm lower than its recently assigned value. As a consequence, ∆47, CDES 90 values of samples having relatively low temperatures of formation are not consistent with ∆47, I-CDES values. We show that GU1, a synthetic carbonate deriving from the hydroxylation of CO2 and exhibiting a strong anti-clumped ∆48, CDES 90 value, appears to be homogeneous in its isotopic composition. If used in combination with ETH-1, −2 and − 3, it may allow projection of background corrected raw data without any bias into ∆47-∆48 CDES 90 space, provided our long-term dual clumped isotope values for these carbonate anchors are considered.Stability of mass spectrometric measurements is related to filament age and/or room temperature fluctuations and can be monitored using reference gas m/z49 intensity. Under the most stable analytical conditions, the ∆49, CDES 90 values of equilibrated gases and carbonates reveal a trend with formation temperature. Using data from the most stable sessions, we present a temperature calibration for ∆49, CDES 90 in CO2 evolved from phosphoric acid digestion of carbonates.

3D-printed film architecture via automatic micro 3D-printing system: Micro-intersection engineering of V2O5 thin/thick films for ultrafast electrochromic energy storage devices

Existing approaches to develop electrochromic (EC) energy storage devices typically focus on the modification of active materials toward a porous morphology, crystallinity, heteroatom-doping, and hybridization/composites with functional materials; however, these approaches may be unsuitable for the full commercialization of EC energy storage devices owing to their complex and expensive processes and incompatibility with large-scale and mass production. Herein, we fabricate 3D-printed film architectures for ultrafast EC energy storage devices, including micro-intersections of vanadium oxide (VO) thin/thick films, via an automatic micro 3D-printing system without active material modification. The micro-intersection originates from the one-pot 3D-printing of vertical lines, creating VO grid-micropatterns with nanoscale thin/thick films on fluorine-doped tin oxide (FTO)/glass. The micro-intersection density was engineered by adjusting the number of printed-lines per unit area and optimized micro-intersection density (OD-3DVO) allows enhanced behaviors of electrons and Li-ions as follows: (i) the thin film architecture alleviates rate-limiting processes that produce sluggish electron transfer and ionic diffusion kinetics by shortening transport channels between FTO and the electrolyte, thereby accelerating ultrafast charge transport. (ii) Micro-width/nano-depth 3D-wells induce capillary force pumping and deep electrolyte infiltration at the interface, thereby enhancing electrolyte wettability. (iii) grid-micropatterned film morphology provides extensive redox sites and high visible transmissivity; thus, the OD-3DVO active layers in EC energy storage devices featured simultaneously enhanced optical and energy storage performances, especially ultrafast switching speeds (0.7 and 0.9 s for coloration and bleaching) and record-high areal energy density at high areal power density (14.03 µWh/cm2 at 25 mW/cm2).

Effects of a Standardized Hydrogenated Extract of Curcumin (Curowhite™) on Melanogenesis: A Pilot Study

The stimulation of melanogenesis by novel natural products is desirable for cosmetic applications such as skin tanning, anti-greying, and clinical use for treating vitiligo and leukoderma disorders. Microphthalmia transcription factor (MITF) is a central transcription factor that controls the expression of tyrosinase, which is a key enzyme responsible for catalyzing the rate-limiting processes of melanin production. Tetrahydrocurcuminoids (THCr), which mostly consist of tetrahydrocurcumin (THC), are a colorless bioactive mixture derived from curcuminoids that are extracted from the Curcuma longa plant. THCr has been reported to exhibit superior properties, including antioxidant and anti-inflammatory effects. Our previous study reported the greater melanogenesis-stimulating effects of purified THC, compared to hexahydrocurcumin (HHC) or octahydrocurcumin (OHC). Curowhite™ (CW) is a proprietary extract that consists of 25% hydrogenated curcuminoids (mixture of THCr, hexahydrocurcuminoids, and octahydrocurcuminoids) encapsulated in a β-cyclodextrin (βCyD) excipient. The encapsulation of THCr in a suitable excipient, such as the widely popular cyclodextrins, helps to enhance the stability, solubility, and bioavailability of the THCr. CW is marketed as a nutraceutical with GRAS status and is safe when administered orally, as shown in vivo studies. However, the impact of CW on melanogenesis remains unexplored. Herein, the impact of CW on melanogenesis were investigated using B16F10 and MNT-1 cells. Our findings show that CW is markedly cytotoxic to B16F10 cells without affecting the cellular melanin content. However, in MNT-1 cells, CW significantly stimulated intracellular melanin content over the concentration range (20–60 µg/mL) with increased dendrite formation while being nontoxic to MNT-1 cells or HaCaT cells after a 5-day treatment. Examination of the effects of the excipient βCyD on cytotoxicity and melanogenesis confirmed that the excipient had no contribution to the biological impacts that were found to be exclusively attributable to the encapsulated mixture (THCr). The mechanisms of CW’s promelanogenic effects in MNT-1 cells were found to be related, at least in part, to an increase in tyrosinase and MITF protein levels, as CW did not alter tyrosinase activity in MNT-1 cells. Moreover, CW exhibited antioxidant activity as obtained through DPPH radical scavenging assay. Together, the findings of this pilot study indicate that CW might hold an exciting avenue as a pro-pigmenting nutraceutical for treating hypopigmentation disorders, the detailed mechanisms of which warrant further exploration. Moreover, future investigations are necessary to examine CW’s effects on melanogenesis in normal human melanocytes and in vivo studies.

Isotopic disequilibrium in brachiopods disentangled with dual clumped isotope thermometry

The stable oxygen and clumped isotope composition of brachiopod calcite are important proxies for the reconstruction of Phanerozoic seawater temperatures and δ18O values. The utility of brachiopods as a temperature archive is nonetheless challenged by indications that their shells precipitate out of isotopic equilibrium with ambient seawater, though the origin of disequilibrium effects has remained elusive. Here, we apply the recently developed dual clumped isotope thermometer (i.e., the simultaneous measurement of Δ47 and Δ48 values in CO2 derived from the acid digestion of carbonates) to modern and fossil brachiopods to investigate disequilibrium signatures recorded in brachiopod calcite. We present evidence that disequilibrium signatures are derived from the combination of two rate-limiting processes: the hydration/hydroxylation of CO2, and, potentially, the diffusion of HCO3−/CO32− in water. An empirical correction for clumped isotope disequilibrium is presented, based on correlation between measured disequilibrium offsets in the Δ47 and Δ48 values of modern brachiopods (Δ47disequilibrium = –0.88 × Δ48disequilibrium + 0.02). Dual clumped isotope thermometry of Eocene age brachiopods from Seymour Island (∼65 °S) yields temperatures in agreement with previously reported Δ47 derived temperatures from coeval bivalves. In contrast, uncorrected Δ47 derived temperatures from the same brachiopods are 6–11 °C colder. Measurement of dual clumped isotope composition alongside δ18O values of brachiopod carbonate should also enable more accurate reconstruction of seawater-δ18O. In comparison with group-specific Δ47-temperature calibrations, which correct for an average kinetic bias in Δ47, dual clumped isotope thermometry accounts for the magnitude of disequilibrium inherent to an individual sample, facilitating more reliable paleotemperature and seawater-δ18O reconstructions.

Identification of key degraders for controlling toxicity risks of disguised toxic pollutants with division of labor mechanisms in activated sludge microbiomes: Using nonylphenol ethoxylate as an example

Efficient management of disguised toxic pollutants (DTPs), which can undergo microbial degradation and convert into more toxic substances, necessitates the collaboration of diverse microbial populations in wastewater treatment plants. However, the identification of key bacterial degraders capable of controlling the toxicity risks of DTPs through division of labor mechanisms in activated sludge microbiomes has received limited attention. In this study, we investigated the key degraders capable of controlling the risk of estrogenicity associated with nonylphenol ethoxylate (NPEO), a representative DTP, in textile activated sludge microbiomes. The results of our batch experiments revealed that the transformation of NPEO into NP and subsequent NP degradation were the rate-limiting processes for controlling the risk of estrogenicity, resulting in an inverted V-shaped curve of estrogenicity in water samples during the biodegradation of NPEO by textile activated sludge. By utilizing enrichment sludge microbiomes treated with NPEO or NP as the sole carbon and energy source, a total of 15 bacterial degraders, including Sphingbium, Pseudomonas, Dokdonella, Comamonas, and Hyphomicrobium, were identified as capable of participating in these processes, Among them, Sphingobium and Pseudomonas were the two key degraders that could cooperatively interact in the degradation of NPEO with division of labor mechanisms. Co-culturing Sphingobium and Pseudomonas isolates exhibited a synergistic effect in degrading NPEO and reducing estrogenicity. Our study underscores the potential of the identified functional bacteria for controlling estrogenicity associated with NPEO and provides a methodological framework for identifying key cooperators engaged in labor division, contributing to the management of risks associated with DTPs by leveraging intrinsic microbial metabolic interactions.

Rate-limiting recovery processes in neurotransmission under sustained stimulation

At active zones of chemical synapses, an arriving electric signal induces the fusion of vesicles with the presynaptic membrane, thereby releasing neurotransmitters into the synaptic cleft. After a fusion event, both the release site and the vesicle undergo a recovery process before becoming available for reuse again. Of central interest is the question which of the two restoration steps acts as the limiting factor during neurotransmission under high-frequency sustained stimulation. In order to investigate this problem, we introduce a non-linear reaction network which involves explicit recovery steps for both the vesicles and the release sites, and includes the induced time-dependent output current. The associated reaction dynamics are formulated by means of ordinary differential equations (ODEs), as well as via the associated stochastic jump process. While the stochastic jump model describes the dynamics at a single active zone, the average over many active zones is close to the ODE solution and shares its periodic structure. The reason for this can be traced back to the insight that recovery dynamics of vesicles and release sites are statistically almost independent. A sensitivity analysis on the recovery rates based on the ODE formulation reveals that neither the vesicle nor the release site recovery step can be identified as the essential rate-limiting step but that the rate-limiting feature changes over the course of stimulation. Under sustained stimulation, the dynamics given by the ODEs exhibit transient changes leading from an initial depression of the postsynaptic response to an asymptotic periodic orbit, while the individual trajectories of the stochastic jump model lack the oscillatory behavior and asymptotic periodicity of the ODE-solution.