Entropy in catalyst dynamics under confinement.

Entropy during the dynamic structural evolution of catalysts has a non-trivial influence on chemical reactions. Confinement significantly affects the catalyst dynamics and thus impacts the reactivity. However, a full understanding has not been clearly established. To investigate catalyst dynamics under confinement, we utilize the active learning scheme to effectively train machine learning potentials for computing free energies of catalytic reactions. The scheme enables us to compute the reaction free energies and entropies of O2 dissociation on Pt clusters with different sizes confined inside a carbon nanotube (CNT) at the timescale of tens of nanoseconds while keeping ab initio accuracy. We observe an entropic effect owing to liquid-to-solid phase transitions of clusters at finite temperatures. More importantly, the confinement effect enhances the structural dynamics of the cluster and leads to a lower melting temperature than those of the bare cluster and cluster outside the CNT, consequently facilitating the reaction to occur at lower temperatures and preventing the catalyst from forming unfavorable oxides. Our work reveals the important influence of confinement on structural dynamics, providing useful insight into entropy in dynamic catalysis.

Biphasic Dose-Response of Mn-Induced Mitochondrial Damage, PINK1/Parkin Expression, and Mitophagy in SK-N-SH Cells.

Excessive manganese (Mn) exposure produces neurotoxicity with mitochondrial damage. Mitophagy is a protective mechanism to eliminate damaged mitochondria to protect cells. The aim of this study was to determine the dose-response of Mn-induced mitochondria damage, the expression of mitophagy-mediated protein PINK1/Parkin and mitophagy in dopamine-producing SK-N-SH cells. Cells were exposed to 0, 300, 900, and 1500 µM Mn2+ for 24 h, and ROS production, mitochondrial damage and mitophagy were examined. The levels of dopamine were detected by ELISA and neurotoxicity and mitophagy-related proteins (α-synuclein, PINK1, Parkin, Optineurin, and LC3II/I) were detected by western blot. Mn increased intracellular ROS and apoptosis and decreased mitochondrial membrane potential in a concentration-dependent manner. However, at the low dose of 300 µM Mn, autophagosome was increased 11-fold, but at the high dose of 1500 µM, autophagosome was attenuated to 4-fold, together with decreased mitophagy-mediated protein PINK1/Parkin and LC3II/I ratio and increased Optineurin expression, resulting in increased α-synuclein accumulation and decreased dopamine production. Thus, Mn-induced mitophagy exhibited a novel biphasic regulation: at the low dose, mitophagy is activated to eliminate damaged mitochondria, however, at the high dose, cells gradually loss the adaptive machinery, the PINK1/Parkin-mediated mitophagy weakened, resulting in neurotoxicity.

Structural dynamics of Ru clusters during nitrogen dissociation in ammonia synthesis.

The dynamic evolution of catalyst structures greatly influences the reactivity, especially sub-nanometer clusters, exhibiting complex configurational fluctuation. In the present work, we study the structural dynamics of a Ru19 cluster during the dissociation of N2 and calculate the reaction free energies using ab initio molecular dynamics (AIMD). Our AIMD calculation predicts a peak-shaped reaction entropy curve due to the adsorption-induced phase transition of the Ru19 cluster. The low melting points of sub-nanometer clusters make it possible to activate N2 at low temperatures. This work demonstrates that the dynamic changes of cluster structures have a non-negligible effect on reaction free energy and offer an opportunity for achieving ammonia synthesis under mild conditions.

Size-dependent phase transitions boost catalytic activity of sub-nanometer gold clusters.

The characterization and identification of the dynamics of cluster catalysis are crucial to unraveling the origin of catalytic activity. However, the dynamical catalytic effects during the reaction process remain unclear. Herein, we investigate the dynamic coupling effect of elementary reactions with the structural fluctuations of sub-nanometer Au clusters with different sizes using ab initio molecular dynamics and the free energy calculation method. It was found that the adsorption-induced solid-to-liquid phase transitions of the cluster catalysts give rise to abnormal entropy increase, facilitating the proceeding of reaction, and this phase transition catalysis exists in a range of clusters with different sizes. Moreover, clusters with different sizes show different transition temperatures, resulting in a non-trivial size effect. These results unveil the dynamic effect of catalysts and help understand cluster catalysis to design better catalysts rationally.

Manganese Intoxication Recovery and the Expression Changes of Park2/Parkin in Rats.

Occupational overexposure to manganese (Mn) produces Parkinson's disease-like manganism. Acute Mn intoxication in rats causes dopaminergic neuron loss, impairment of motor activity and reduction of the expression of Park2/Parkin. The expression of Park2/Parkin is also reduced. Whether these changes are reversible after cessation of Mn exposure is unknown, and is the goal of this investigation. Adult male rats were injected with Mn2+ at doses 1 mg/kg and 5 mg/kg in the form of MnCl2·4H2O, every other day for one-month to produce acute Mn neurotoxicity. For a half of rats Mn exposure was suspended for recovery for up to 5 months. Mn neurotoxicity was evaluated by the accumulation of Mn in blood and brain, behavioral activities, dopaminergic neuron loss, and the expression of Park2/Parkin in the blood cells and brain. Dose-dependent Mn neurotoxicity in rats was evidenced by Mn accumulation, rotarod impairments, reduction of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra, decreased level of Park2 mRNA in the blood and brain, and decreased Parkin protein in the brain. After cessation of Mn exposure, the amount of Park2 mRNA in the blood started to increase one month after the recovery. After 5-month of recovery, blood and brain Mn returned to normal, rotarod activity recovered, the reduction of TH-positive dopaminergic neurons ameliorated, and the level of Park2 mRNA in the blood and Park2/Parkin in the midbrain and striatum were returned to the normal. Mn neurotoxicity in rats is reversible after cessation of Mn exposure. The level of Park2 mRNA in the blood could be used as a novel biomarker for Mn exposure and recovery.

Size-Sensitive Dynamic Catalysis of Subnanometer Cu Clusters in CO2 Dissociation.

Small cluster catalysts are highly size-dependent and exhibit complex structural dynamic effects during catalytic reactions. Understanding their structural dynamics is of great importance in tuning the catalytic performances of small clusters that widely exist in supported catalysts. However, very little is known about the size dependence of the dynamic effect of small clusters. In this work, we systematically study the free energies and barriers of catalytic dissociation of CO2 at different temperatures on dynamical Cu clusters with different sizes by ab initio molecular dynamics. The reaction shows an abnormal entropic effect on Cu clusters, and more interestingly, it shows size sensitivity. On the Cu7 cluster, the entropy curve shows a reverse peak shape with increasing temperature, and it is surprising to find that it has a complex pulse shape on the Cu19 cluster. The detailed analysis shows that such temperature dependences can be attributable to the nontrivial behaviors of adsorption-induced phase transitions of the subnanometer Cu clusters during the dissociation of CO2. Our work not only demonstrates the complexity of the temperature dependence of the surface reaction on cluster sizes but also provides useful insight into the phase transition catalysis of dynamic clusters.

Molecular origin of negative component of Helmholtz capacitance at electrified Pt(111)/water interface.

Electrified solid/liquid interfaces are the key to many physicochemical processes in a myriad of areas including electrochemistry and colloid science. With tremendous efforts devoted to this topic, it is unexpected that molecular-level understanding of electric double layers is still lacking. Particularly, it is perplexing why compact Helmholtz layers often show bell-shaped differential capacitances on metal electrodes, as this would suggest a negative capacitance in some layer of interface water. Here, we report state-of-the-art ab initio molecular dynamics simulations of electrified Pt(111)/water interfaces, aiming at unraveling the structure and capacitive behavior of interface water. Our calculation reproduces the bell-shaped differential Helmholtz capacitance and shows that the interface water follows the Frumkin adsorption isotherm when varying the electrode potential, leading to a peculiar negative capacitive response. Our work provides valuable insight into the structure and capacitance of interface water, which can help understand important processes in electrocatalysis and energy storage in supercapacitors.

Adsorption-Induced Liquid-to-Solid Phase Transition of Cu Clusters in Catalytic Dissociation of CO2.

Sub-nanometer metal clusters widely existing in catalysts have a large ensemble of metastable isomers that can interconvert during catalytic reactions, exhibiting complex dynamical catalytic effects. In this work, we systematically investigate the temperature dependent structural dynamics of the Cu13 cluster in CO2 dissociation using ab initio molecular dynamics and the free energy calculation method. We find an abnormal entropic effect due to adsorption-induced liquid-to-solid phase transition of the cluster during the course of the elementary dissociation step at transition temperatures. In the dissociation product, the formation of a rigid Cu3O unit decreases the dynamical fluidity of the cluster and increases the melting temperature, causing a decrease in the entropy of the dissociation product. Our work demonstrates the nontrivial effects of surface adsorption on phase transition behaviors of dynamic clusters and offers a new perspective to dynamic catalysis.

Chronic Manganese Administration with Longer Intervals Between Injections Produced Neurotoxicity and Hepatotoxicity in Rats.

Subacute exposure to manganese (Mn) produced Parkinson's disease-like syndrome called Manganism. Chronic onset and progression are characteristics of Manganism, therefore, this study aimed to examine Mn toxicity following chronic exposures. Male Sprague-Dawley rats were injected Mn2+ 1 and 5 mg/kg, every 10 days for 150 days (15 injections). Animal body weight and behavioral activities were recorded. At the end of experiments, the brain and liver were collected for morphological and molecular analysis. Chronic Mn exposure did not affect animal body weight gain, but the high dose of Mn treatment caused 20% mortality after 140 days of administration. Motor activity deficits were observed in a dose-dependent manner at 148 days of Mn administration. Immunofluorescence double staining of substantia nigra pars compacta (SNpc) revealed the activation of microglia and loss of dopaminergic neurons. The chronic neuroinflammation mediators TNFα, inflammasome Nlrp3, Fc fragment of IgG receptor IIb, and formyl peptide receptor-1 were increased, implicating chronic Mn-induced neuroinflammation. Chronic Mn exposure also produced liver injury, as evidenced by hepatocyte degeneration with pink, condensed nuclei, indicative of apoptotic lesions. The inflammatory cytokines TNFα, IL-1ß, and IL-6 were increased, alone with stress-related genes heme oxygenase-1, NAD(P)H:quinone oxidoreductase-1 and metallothionein. Hepatic transporters, such as multidrug resistant proteins (Abcc1, Abcc2, and Abcc3) and solute carrier family proteins (Slc30a1, Slc39a8 and Slc39a14) were increased in attempt to eliminate Mn from the liver. In summary, chronic Mn exposure produced neuroinflammation and dopaminergic neuron loss in the brain, but also produced inflammation to the liver, with upregulation of hepatic transporters.

Joint neurodevelopmental and behavioral effects of nonylphenol and estradiol on F1 male rats.

The purpose of present study is to examine whether gestational exposure of two major environmental endocrine-disrupting chemicals, nonylphenol (NP) and estradiol (E2), would affect nervous system development of offspring rats and explore the joint effects of NP and E2. After impregnation, dams were assigned to seven groups. The first and second groups received gavage with NP at dose levels of 50 mg/kg/day (NP-L) and 100 mg/kg/day (NP-H); the third and fourth groups were gavaged with E2 at dose levels of 10 µg/kg/day (E2-L) and 20 µg/kg/day (E2-H); the fifth and sixth groups were gavaged with joint NP and E2 [NP 50 mg/kg/day + E2 10 µg/kg/day (NP-E2-L) and NP 100 mg/kg/day+E2 20 µg/kg/day (NP-E2-H)] dissolved in groundnut oil; and the seventh group was orally administered with groundnut oil alone (vehicle control; 2 ml/kg/day), respectively, daily from gestational days 9 to 15 (transplacental exposures). Compared to the control, exclusive NP and E2 treatment groups, joint exposure to NP-E2-L and NP-E2-H has both produced a significant decrease in mean litter size and number of live pups per litter in dams; Offspring rats spent more time to perform cliff-drop aversion reflex, surface righting reflex, air righting reflex, auditory startle, and visual placing; In Morris water maze task, an increased escape latency was presented in offspring rats; In step-down avoidance test, offspring rats jointly exposed to NP and E2 spent more reaction time. Decrease in acetylcholinesterase activity and increase in choline acetyltransferase activity were observed in the hippocampus of offspring rats. Gestational joint exposure to NP and E2 might induce nervous development impairment of offspring rats. Moreover, additive toxic effects of NP and E2 on nervous development have been identified among offspring rats as well.

Protective effects of dietary fibre against manganese-induced neurobehavioral aberrations in rats.

We tested the hypothesis that dietary fibre (DF) has protective effects against manganese (Mn)-induced neurotoxicity. Forty-eight one-month old Sprague-Dawley rats were randomly divided into six groups: control, 16 % DF, Mn (50 mg kg-1 body weight), Mn+ 4 % DF, Mn+ 8 % DF, and Mn+ 16 % DF. After oral administration of Mn (as MnCl2) by intragastric tube during one month, we determined Mn concentrations in the blood, liver, cerebral cortex, and stool and tested neurobehavioral functions. Administration of Mn was associated with increased Mn concentration in the blood, liver, and cerebral cortex and increased Mn excretion in the stool. Aberrations in neurobehavioral performance included increases in escape latency and number of errors and decrease in step-down latency. Irrespective of the applied dose, the addition of DF in forage decreased tissue Mn concentrations and increased Mn excretion rate in the stool by 20 % to 35 %. All neurobehavioral aberrations were also improved. Our findings show that oral exposure to Mn may cause neurobehavioral abnormalities in adult rats that could be efficiently alleviated by concomitant supplementation of DF in animal feed.

[Early biological markers of manganese exposure].

OBJECTIVE: To explore the biomarker of manganese exposure by analyzing the relationship between manganese exposure and concentration in some biomaterials. METHODS: The air samples were collected through the individual air sample. According to the manganese levels in the air, workers were assigned to control group, low concentration group and high concentration group, and manganese in the hair, urine, serum, blood cell and saliva from different group were measured respectively. The correlations between concentration of external manganese exposure and manganese concentrations in biomaterials, and years of employment and concentrations in biomaterials were analyzed. RESULTS: In the high concentration group, saliva manganese was 32.17 µg/L, hair manganese was 37.39 mg/kg, urine manganese was 2.50 µg/L, plasma manganese was 29.61 µg/L, blood manganese was 14.49 µg/L, were higher than those in the control group (10.40 µg/L, 1.60 mg/kg, 0.77 µg/L, 10.30 µg/L, 4.56 µg/L respectively) (P < 0.01). The manganese concentration in the saliva was significantly correlated with airborne manganese concentration (r = 0.649, P < 0.01), with the years of employment (r = 0.404, P < 0.01), with the total exposure of manganese (r = 0.342, P < 0.01), with the manganese concentration of plasma (r = 0.303, P < 0.01) and with the manganese concentration in blood cells (r = 0.359, P < 0.01), respectively. CONCLUSIONS: The concentration of manganese in saliva could work as a biomarker of manganese internal exposure.

Toxic effect of gestational exposure to nonylphenol on F1 male rats.

OBJECTIVE: The purpose of this study was to examine whether gestational exposure to major environmental endocrine-disrupting chemicals, nonylphenol (NP), would lead to nerve behavioral and learning and memory capacity alterations in the male offspring of rats, and reproductive development alterations in the male offspring of rats. METHODS: Dams were gavaged with NP at a dose level of 50 mg/kg/day, 100 mg/kg/day or 200 mg/kg/day daily from gestational day 9 to 15, and at a dose level of 40 mg/kg/day, 80 mg/kg/day or 200 mg/kg/day daily from gestational day 14 to 19 (transplacental exposures). RESULTS: Exposure to 200 mg/kg/day NP produced a significant decrease in learning and memory functions in offspring rats (P<0.05) in Morris water maze task, as demonstrated by the increased escape latency and number of error. In Step-down Avoidance Test, offspring rats exposed to NP spent more reaction time (RT) and presented lower latency to first step-down than the control offspring (P<0.01). In utero exposure to 80 and 200 mg/kg/day NP produced a significant decrease in the number of live pups per litter and ratio of anogenital distance to body length on PND 0 (P<0.05), and also testes and prostate weight, activities of ALP, plasma testosterone concentration, cauda epididymis sperm counts, daily sperm production et al. respectively on PND 90 (P<0.05). Histopathological examination of the brain biopsy illustrates that exposure to NP at high dose induces the presence of abnormal distribution of spermatozoa showed in lumina of the seminiferous tubules, and absence of spermatogenesis and spermiogenesis. CONCLUSION: Gestational exposure to nonylphenol might induce neurotoxic and reproductive toxic effects on F1 male rats.

[Preliminary study of biomarker in blood or cerebrospinal fluid of rat following manganese exposure].

OBJECTIVE: To explore the biomarkers of manganese exposure by measuring the manganese (Mn) and iron (Fe) level as well as the mRNA change of Hepcidin, divalent metal-ion transporter-1 (DMT1) and Parkin-2, one of genes related to Parkinson disease in body fluid and brain tissues of rat. METHODS: Male Sprague-Dawley rats were administered (i.p) either MnCl2 solution (6 mg Mn/kg) or the same volume saline, 5 times per week and for 4 weeks. Graphic furnace Atom Absorption Spectrum (AAS) was applied to measure the concentration of Mn and Fe in brain tissue and body fluids. Meanwhile Hepcidin, DMT1 and Parkin-2 mRNA expression were detected by real-time RT-PCR. RESULTS: Mn concentration in erythrocytes of rats was the 86.9 folds of that in control; No significant change was found in plasma. However the trend and range of Mn increase in cerebrospinal fluid (CSF) was the same as that in brain tissue including striatum, cortex, hippocampus and choroid plexus. Meanwhile Fe concentration in brain tissue of Mn exposed rats was also higher than that of control, whose trend was as same as that in CSF. However iron concentration in plasma decreased. The real-time RT-PCR data also showed that Hepcidin mRNA expression in Mn-exposed rat decreased 56% in blood, which was in line with its expression in cortex(67%). Similarly, Parkin-2 mRNA expression decreased both in blood (42%) and in striatum. However DMT1 mRNA expression increase 38% in striatum of Mn-exposed rats but decreased in blood. CONCLUSION: Hepcidin and Parkin-2 mRNA expression in blood might be serves as the effective biomarkers following manganese exposure, certainly which needs to be further explored.

[Effects of nonylphenol exposure via placenta on early nervous reflex and locomotives of offspring in rat].

OBJECTIVE: To explore the influence of nonylphenol (NP) on the neural behavioral development of filial generation rats exposed via placenta. METHODS: On the first day of the pregnancy, the SD rats were divided into four groups, and orally administered with NP at doses of 0, 50, 100 and 200 mg/kg on gestational day 9 approximately 15 respectively. The offspring rats of each groups were examined to observe the impact of NP on the early physiological, neurobehavioral development. The changes of filial generation body weight (from generation day 1 to 28) were measured. Brain tissues were stained with Hematoxylin-eosin and Congo red to observe with optical microscope. RESULTS: In contrast to the control group, the early physiological markers (pinna detachment, hair growth, tooth growth and eye opening) and the early neurobehavioral development indices (surface righting, air righting, acoustic startle and visual placing) were significantly delayed in the groups of NP 200mg/kg dose (P < 0.05). The developing time of physiological markers decreased from (4.5 +/- 0.8, 5.2 +/- 0.8, 12.7 +/- 1.4, 16.0 +/- 1.7) d to (3.6 +/- 0.5, 3.6 +/- 0.5, 11.1 +/- 1.1, 12.7 +/- 1.3) d while neurobehavioral developing time decreased from (6.5 +/- 0.8, 11.3 +/- 0.5, 11.2 +/- 1.0, 20.2 +/- 1.0) d to (5.1 +/- 0.4, 8.3 +/- 0.5, 9.3 +/- 0.5, 9.3 +/- 0.5) d (P < 0.05 or P < 0.01). The body weights of filial generation rats were decreased obviously from 1 st day to 28th day. Histopathological examination displayed that hippocampal neurons had congestion and oedema in the group of 100, 200 mg/kg dose. CONCLUSION: Exposures to NP during gestation might impair the neurobehavioral development of F1 rats significantly.