Mechanisms, Growth Rates, and Morphologies of Gas Hydrates of Carbon Dioxide, Methane, and Their Mixtures

Mechanisms of growth and dissociation, growth rates, and morphology of gas hydrates of methane, carbon dioxide, and two CH4:CO2 mixtures (80:20 and 30:70 nominal concentration) were studied using using high resolution images and very precise temperature control. Subcooling and a recently proposed mass transfer-based driving force were used to analyze the results. When crystal growth rates did not exceed 0.01 mm/s, all systems showed faceted, euhedral crystal habits at low driving forces. At higher driving forces and growth rates, morphologies were different for all systems. These results solve apparent contradictions in literature about the morphology of hydrates of methane, carbon dioxide, and their mixtures. Differences in the growth mechanism of methane-rich and carbon dioxide-rich hydrates were elucidated. It was also shown that hydrate growth of methane, carbon dioxide, and their mixtures proceed via partial dissociation of the growing crystal. Temperature gradients were used to dissociate hydrates at specific locations, which revealed a most interesting phenomenon: On dissociation, carbon dioxide-rich hydrates propagated onto the bare substrate while drawing water from the opposite side of the sample. Furthermore, it was shown that an abrupt change in morphology common to all systems could be correlated to a change in the slope of growth rate data. This change in morphology was explained by a shift in the crystal growth mechanism.

A Spectroscopic Paradox: The Interaction of Methanol with ZSM-5 at Room Temperature

The adsorption of methanol in HZSM-5 at low temperatures has long been regarded as an associative process involving hydrogen bonding to the acidic zeolite hydroxyl groups. Recent studies employing inelastic neutron scattering spectroscopy (INS) have reported that complete dissociation to methoxylate the zeolite occurs at 298 K, and infrared evidence for a partial dissociation at 298 K has also been described. Here we investigate the apparent contradictions between different techniques, using a combination of INS, infrared spectroscopy and solid-state NMR spectroscopy, including isotopic substitution experiments. Different possible explanations are proposed and considered; we conclude that at room temperature methanol is very largely associatively adsorbed, although the presence of some small extent (>1%) of methoxylation cannot be ruled out.

Dissociable Contribution of Extrastriate Responses to Representational Enhancement of Gaze Targets

Before saccadic eye movements, our perception of the saccade targets is enhanced. Changes in the visual representation of saccade targets, which presumably underlie this perceptual benefit, emerge even before the eye begins to move. This perisaccadic enhancement has been shown to involve changes in the response magnitude, selectivity, and reliability of visual neurons. In this study, we quantified multiple aspects of perisaccadic changes in the neural response, including gain, feature tuning, contrast response function, reliability, and correlated activity between neurons. We then assessed the contributions of these various perisaccadic modulations to the population's enhanced perisaccadic representation of saccade targets. We found a partial dissociation between the motor information, carried entirely by gain changes, and visual information, which depended on all three types of modulation. These findings expand our understanding of the perisaccadic enhancement of visual representations and further support the existence of multiple sources of motor modulation and visual enhancement within extrastriate visual cortex.

Anticancer Potency of Copper(I) Complexes Against a Range Cancer Cell Lines: A Review

The copper(I) complexes of N,N-diimine, N,O- and/or N, S-bidentate systems perform significant dose-dependent anticancer activity toward various cell lines viz. MCF-7, LNCap, PSN-1, A431, BxPC3, H157, A2780, HeLa, MDA-MB231, MGC-803 etc. The copper(I) complexes can cross the cellular plasmalemma that results in the accumulation of copper ion in the cancer cells, exhibit significant anticancer effect and overcome the multidrug resistance because these can slightly induce the DNA cleavage as a result of limited generation of reactive oxygen species (ROS). Copper(I) complexes exhibit significantly higher broad-spectrum antiproliferation and cell apoptosis via mitochondrial pathway than that of their corresponding Cu(II), Co(II), Pd(II), and Ni(II) complexes. The copper(I) complexes inhibit the cancer cells not only via ROS generation but also via DNA interactions possibly by attacking the sugar-phosphate backbone of DNA due to their oxidative and partial dissociation behavior. Copper(II/I) complexes are also able to cleave DNA by hydrolytic pathway and induce caspase-dependent-mitochondrial-mediated cell apoptosis by ROS production or blocking the progression of cell cycles. In many cases, the modification in organic moiety and the placement of electronegative substituent near the metallic center of complexes have been found to enhance their anticancer potency in a significant manner. Thus copper(I) complexes may be used as the better anticancer drugs with multiple modes of action compared to the copper(II) complexes due to having oxidative behavior and generation of empty site on copper(I) ion during partial dissociation.

Dynamic relocalization of cytosolic type III secretion system components prevents premature protein secretion at low external pH

Many bacterial pathogens use a type III secretion system (T3SS) to manipulate host cells. Protein secretion by the T3SS injectisome is activated upon contact to any host cell, and it has been unclear how premature secretion is prevented during infection. Here we report that in the gastrointestinal pathogens Yersinia enterocolitica and Shigella flexneri, cytosolic injectisome components are temporarily released from the proximal interface of the injectisome at low external pH, preventing protein secretion in acidic environments, such as the stomach. We show that in Yersinia enterocolitica, low external pH is detected in the periplasm and leads to a partial dissociation of the inner membrane injectisome component SctD, which in turn causes the dissociation of the cytosolic T3SS components. This effect is reversed upon restoration of neutral pH, allowing a fast activation of the T3SS at the native target regions within the host. These findings indicate that the cytosolic components form an adaptive regulatory interface, which regulates T3SS activity in response to environmental conditions.

ELECTRO-OSMOTIC FRACTIONATION OF HYDROGEN ISOTOPES IN ELECTROLYTIC SOLUTIONS USING COMPOSITE PROTON-PERMEABLE MEMBRANES

Based on the analysis of the features of electroosmotic processes that are implemented in proton-conducting membranes, the possibility of fractioning hydrogen isotopes in electrolytes formed using tritiated water (HTO) is estimated. The interaction of the solution with the membranes in their channels leads to polarization and partial dissociation of the electrolyte molecules. In water molecules, when protium is replaced by a heavy isotope of hydrogen, the energy of breaking of hydrogen bonds increases and the process of their dissociation proceeds predominantly according to the scheme: HTO ↔ H+ + TO—. A part of the released protons can join water molecules to form the H3O+ ion. H3O+ and TO— ions are more mobile than other singly charged ions. The main characteristic that determines the suitability of electroosmotic membranes to the fractionation of hydrogen isotopes is proton conductivity. The released protons have anomalously high mobility due to their small size, tunnel and relay movement through hydrogen bonds between adjacent polar groups in the channels of the proton-conducting membranes. To ensure high proton conductivity in the pores and channels of the membranes, modifying substances are fixed, which contain the groups: –ОН- , –NH2, –NH, –SH, –COOH, –SO3H, acid salts and oxides, containing surface proton-conducting groups. To create proton-conducting membranes, it is possible to use surface-modified β-alumina (β-Al2O3(H3O+)) and protonated (H3O+) montmorillonite with ionic conductivity (5х103 – 4х104 Ohm х cm–1). The most effective are surface modifiers with negatively charged sulfonic groups. The imposition of an external electric field leads to the movement of ions in the electrolyte, which leads to a redistribution of the isotope ratio in the near-anode and cathode spaces.

DEET Degradation by Titanium Dioxide–Zeolite Nanocomposites: Effects of Aggregation State, Water Chemistry, and Natural Organic Matter

Immobilization of titanium dioxide nanoparticles (TiO₂ NPs) facilitates their removal and reuse in water treatment applications. Composite materials of electrostatically-bound TiO₂ NPs and zeolite particles have been proposed, but limited mechanistic studies are available on their performance in complex media. This study delineates the relative importance of homo- and heteroaggregation, water chemistry, and surface fouling by natural organic matter (NOM) on the photocatalytic degradation of diethyltoluamide (DEET) by TiO₂-zeolite composites. Zeolite adsorbs a portion of the DEET, rendering it unavailable for degradation; corrections for this adsorption depletion allowed appropriate comparison of the reactivity of the composites to the NPs alone. The TiO₂-zeolite composites showed enhanced DEET degradation in moderately hard water (MHW) compared to deionized water (DIW), likely attributable to the influence of HCO₃⁻, whereas a net decline in reactivity was observed for the TiO₂ NPs alone upon homoaggregation in MHW. The composites also better maintained reactivity in the presence of NOM in MHW, as removal of Ca²⁺ onto the zeolite mitigated fouling of the TiO₂ surface by NOM. However, NOM induced partial dissociation of the composites. DEET byproduct formation, identified by quadrupole–time of flight (QTOF) mass spectrometry, was generally unaffected by the zeolite, while NOM fouling favored de-ethylation over hydroxylation products. Overall, the most significant factor influencing TiO₂ reactivity toward DEET was NOM adsorption, followed by homoaggregation, electrolytes (here, MHW versus DIW), and heteroaggregation. These findings can inform a better understanding of NP reactivity in engineered water treatment applications.

DEET Degradation by Titanium Dioxide–Zeolite Nanocomposites: Effects of Aggregation State, Water Chemistry, and Natural Organic Matter

Immobilization of titanium dioxide nanoparticles (TiO₂ NPs) facilitates their removal and reuse in water treatment applications. Composite materials of electrostatically-bound TiO₂ NPs and zeolite particles have been proposed, but limited mechanistic studies are available on their performance in complex media. This study delineates the relative importance of homo- and heteroaggregation, water chemistry, and surface fouling by natural organic matter (NOM) on the photocatalytic degradation of diethyltoluamide (DEET) by TiO₂-zeolite composites. Zeolite adsorbs a portion of the DEET, rendering it unavailable for degradation; corrections for this adsorption depletion allowed appropriate comparison of the reactivity of the composites to the NPs alone. The TiO₂-zeolite composites showed enhanced DEET degradation in moderately hard water (MHW) compared to deionized water (DIW), likely attributable to the influence of HCO₃⁻, whereas a net decline in reactivity was observed for the TiO₂ NPs alone upon homoaggregation in MHW. The composites also better maintained reactivity in the presence of NOM in MHW, as removal of Ca²⁺ onto the zeolite mitigated fouling of the TiO₂ surface by NOM. However, NOM induced partial dissociation of the composites. DEET byproduct formation, identified by quadrupole–time of flight (QTOF) mass spectrometry, was generally unaffected by the zeolite, while NOM fouling favored de-ethylation over hydroxylation products. Overall, the most significant factor influencing TiO₂ reactivity toward DEET was NOM adsorption, followed by homoaggregation, electrolytes (here, MHW versus DIW), and heteroaggregation. These findings can inform a better understanding of NP reactivity in engineered water treatment applications.

Action imitation via trajectory-based or posture-based planning

Movement imitation is a significant daily activity involved in social interaction and motor learning. Although imitation remains poorly understood, recent research suggests that it may be achieved in two distinct ways. In posture-based imitation, movements reproduce how the body should look and feel, and are sensitive to the relative positioning of body parts. In trajectory imitation, movements mimic the spatiotemporal motion path of the end effector. We hypothesized that people can imitate via either mechanism. If true, we would expect to see a switch cost when individuals change from one mechanism to the other. To test this, twenty-five healthy young adults performed a sequential multitasking imitation task. Participants were first instructed to pay attention to the limb postures or the hand path of a video-recorded model. They next performed an intervening motor task that was neutral, congruent, or incongruent with the instructed imitation type. Finally, participants imitated the modeled movement. Spatiotemporal imitation accuracy was greatest after a neutral intervening task, and worst after posture matching. When the primary task involved imitating trajectories, we observed a switch cost: movements following the posture-matching intervening task were less consistent with baseline (neutral) performance, suggesting performance was disrupted by the incongruence. Incongruent primary and intervening tasks also reduced cross-subject consistency. Such effects were not observed when imitating limb postures. In summary, we observed a partial dissociation between posture matching and trajectory imitation as a result of instructions and intervening tasks that is nevertheless consistent with the existence of two computationally distinct imitation mechanisms.

Efficiency of the four proteasome subtypes to degrade ubiquitinated or oxidized proteins

The proteasome is responsible for selective degradation of proteins. It exists in mammalian cells under four main subtypes, which differ by the combination of their catalytic subunits: the standard proteasome (β1–β2–β5), the immunoproteasome (β1i–β2i–β5i) and the two intermediate proteasomes (β1–β2–β5i and β1i–β2–β5i). The efficiency of the four proteasome subtypes to degrade ubiquitinated or oxidized proteins remains unclear. Using cells expressing exclusively one proteasome subtype, we observed that ubiquitinated p21 and c-­myc were degraded at similar rates, indicating that the four 26S proteasomes degrade ubiquitinated proteins equally well. Under oxidative stress, we observed a partial dissociation of 26S into 20S proteasomes, which can degrade non-ubiquitinated oxidized proteins. Oxidized calmodulin and hemoglobin were best degraded in vitro by the three β5i-containing 20S proteasomes, while their native forms were not degraded. Circular dichroism analyses indicated that ubiquitin-independent recognition of oxidized proteins by 20S proteasomes was triggered by the disruption of their structure. Accordingly, β5i-containing 20S proteasomes degraded unoxidized naturally disordered protein tau, while 26S proteasomes did not. Our results suggest that the three β5i-containing 20S proteasomes, namely the immunoproteasome and the two intermediate proteasomes, might help cells to eliminate proteins containing disordered domains, including those induced by oxidative stress.