Slow Conversion Research Articles

Determination of accurate and precise chromium isotope ratios in seawater samples by MC-ICP-MS illustrated by analysis of SAFe Station in the North Pacific Ocean

Although the cycling of chromium (Cr) in the ocean may have direct implications on the Cr isotope system's application as a paleo-redox proxy, little seawater Cr isotope data has been published. This may be partly due to the analytical challenges associated with the preconcentration and the purification of the nano-molar trace metal Cr from the seawater matrix. Here, we present a reliable method for the determination of accurate and precise 53Cr/52Cr isotope ratios of total chromium (=Cr(III) + Cr(VI)) in seawater, which could be modified to be redox species-specific. Seawater acidification induces the slow conversion of Cr(VI) to Cr(III). Total Cr of the sample and an equilibrated 50Cr-54Cr double spike is preconcentrated as Cr(III) using Mg(OH)2 coprecipitation. Cr captured by the Mg(OH)2 pellet is oxidized to Cr(VI) using (NH4)2S2O8 under carefully controlled pH, temperature and time settings, in order to avoid H2O2 generation and to control sulfur speciation. Taking advantage of the differing charges of Cr(III) and Cr(VI), three AG 1-X8 columns separate Cr from the salt matrix and isobaric interferences V, Ti, and Fe (column 1), sulfur polyatomic interferences (column 2), and Fe traces (column 3). Analysis is conducted on a MC-ICP-MS IsoProbe featuring a hexapole collision cell in low resolution mode. When pure solutions of SRM 979 are processed via this low blank method (~0.017 nmol of Cr), δ53Cr w.r.t. SRM 979 = +0.02 ± 0.06‰ (±2 SD) is obtained (n = 10). Using this technique, the first full water column profile of Cr isotope ratios at a station in the Pacific Ocean (SAFe station, 30°N 140°W) was generated and demonstrates high oceanographic consistency.This article is part of a special issue entitled: “Cycles of trace elements and isotopes in the ocean – GEOTRACES and beyond” - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González.

The regulation of skeletal muscle fiber-type composition by betaine is associated with NFATc1/MyoD.

Increasing evidence indicates that muscular dysfunction or alterations in skeletal muscle fiber-type composition not only are involved in muscle metabolism and function but also can limit functional capacity. Therefore, understanding the mechanisms regulating key events during skeletal myogenesis is necessary. Betaine is a naturally occurring component of commonly eaten foods. Here, we showed that 10mM betaine supplementation in vitro significantly repressed myoblast proliferation and enhanced myoblast differentiation. This effect can be mediated by regulation of miR-29b-3p. Further analysis showed that betaine supplementation in vitro regulated skeletal muscle fiber-type composition through the induction of NFATc1 and the negative regulation of MyoD expression. Furthermore, mice fed with 10mM betaine in water for 133days showed no impairment in overall health. Consistently, betaine supplementation increased muscle mass, promoted muscle formation, and modulated the ratio of fiber types in skeletal muscle in vivo. These findings shed light on the diverse biological functions of betaine and indicate that betaine supplementation may lead to new therapies for diseases such as muscular dystrophy or other diseases related to muscle dysfunction. KEY MESSAGES: Betaine supplementation inhibits proliferation and promotes differentiation of C2C12 myoblasts. Betaine supplementation regulates fast to slow muscle fiber-type conversion and is associated with NFATc1/MyoD. Betaine supplementation enhances skeletal myogenesis in vivo. Betaine supplementation does not impair health of mice.

Efficient Artificial Nucleases for Mediating DNA Cleavage Based on Tuning the Steric Effect in the Pyridyl Derivatives of Tripod Tetraamine‐Cobalt(II) Complexes

Four cobalt(II) complexes [Co(L1)Cl]PF6/ClO4 (C1‐PF6/C1‐ClO4), [Co(L2)Cl]PF6 (C2‐PF6), [Co(L3)Cl]PF6/ClO4·H2O·CH3OH (C3‐PF6/C3‐ClO4·H2O·CH3OH) and [Co(L4)Cl]PF6·2H2O (C4‐PF6·2H2O), in which L1–L4 refer to [(3,5‐dimethyl‐4‐methoxy‐2‐pyridylmethyl)bis(2‐pyridylmethyl)]amine, [(3,4‐dimethoxy‐2‐pyridylmethyl)‐(2‐pyridylmethyl)]amine, [bis(3,5‐dimethyl‐4‐methoxy‐2‐pyridylmethyl)‐(2‐pyridylmethyl)]amine and {[bis(3,4‐dimethoxy‐2‐pyridyl)methyl]‐(2‐pyridylmethyl)}amine, respectively, were synthesized and structurally characterized. Single‐crystal X‐ray crystallography confirmed the trigonal bipyramidal geometries of the complexes. In aqueous acetonitrile solution, the green complexes dissolve with the formation of a yellow solution with biphasic kinetic behavior. In 60 % H2O/CH3CN (by volume) and 25 °C, the first step corresponds to the rapid formation of [Co(L)(CH3CN)]2+ (ka = 0.16–2.0 min–1) followed by a slow conversion into [Co(L)(H2O)]2+ (kb = 6.3 × 10–3–0.10 min–1), where the two species exist in equilibrium. The spectrophotometric and conductometric titrations of the complexes were consistent with the proposed equilibrium. The coordinated H2O in the aqua complexes, [Co(L)(H2O)]2+ have pKa values ranging from 8.3 to 8.5 at 25 °C. All complexes cleaved plasmid DNA at micromolar concentrations within 2 h at 37 °C and pH 7.0 under hydrolytic conditions. Compared to the uncatalyzed cleavage of DNA, rate enhancements of up to 100 million were achieved in case of complex C4‐PF6.

The influence of nitrogen concentration and precipitation on fertilizer production from urine using a trickling filter

Planetary habitation requires technology to maintain natural microbial processes, which make nutrients from biowaste available for plant cultivation. This study describes a 646 day experiment, in which trickling filters were monitored for their ability to mineralize nitrogen when loaded with artificial urine solutions of different concentrations (40, 60, 80 and 100% v/v). Former studies have indicated that increasing urine concentrations slow nitrogen conversion rates and induce growing instability. In the current experiment, nitrogen conversion rates, measured as nitrate production/day, did not differ between concentration levels and increasing instability was not observed. Instead, the buffering capacity of the mussel shells added as buffer system (∼75% calcium carbonate) increased with increasing concentrations of synthetic urine possibly due to the higher phosphate content. The intensified precipitation of calcium phosphates seems to promote carbonate dissolution leading to improved buffering. For space applications, the precipitation of calcium phosphates is not desirable as for the phosphate to be available to the plants the precipitate must be treated with hazardous substances. With regard to terrestrial agriculture the process-integrated phosphate precipitation is a possibility to separate the macronutrients nitrogen and phosphate without addition of other chemicals. Thus, the described process offers a simple and cost-effective approach to fertilizer production from biogenic residues like slurry.

Untargeted metabolomics identifies trimethyllysine, a TMAO-producing nutrient precursor, as a predictor of incident cardiovascular disease risk.

Using an untargeted metabolomics approach in initial (N = 99 subjects) and replication cohorts (N = 1,162), we discovered and structurally identified a plasma metabolite associated with cardiovascular disease (CVD) risks, N6,N6,N6-trimethyl-L-lysine (trimethyllysine, TML). Stable-isotope-dilution tandem mass spectrometry analyses of an independent validation cohort (N = 2,140) confirmed TML levels are independently associated with incident (3-year) major adverse cardiovascular event risks (hazards ratio [HR], 2.4; 95% CI, 1.7-3.4) and incident (5-year) mortality risk (HR, 2.9; 95% CI, 2.0-4.2). Genome-wide association studies identified several suggestive loci for TML levels, but none reached genome-wide significance; and d9(trimethyl)-TML isotope tracer studies confirmed TML can serve as a nutrient precursor for gut microbiota-dependent generation of trimethylamine (TMA) and the atherogenic metabolite trimethylamine N-oxide (TMAO). Although TML was shown to be abundant in both plant- and animal-derived foods, mouse and human fecal cultures (omnivores and vegans) showed slow conversion of TML to TMA. Furthermore, unlike chronic dietary choline, TML supplementation in mice failed to elevate plasma TMAO or heighten thrombosis potential in vivo. Thus, TML is identified as a strong predictor of incident CVD risks in subjects and to serve as a dietary precursor for gut microbiota-dependent generation of TMAO; however, TML does not appear to be a major microbial source for TMAO generation in vivo.

High‐Performance and Low‐Temperature Lithium–Sulfur Batteries: Synergism of Thermodynamic and Kinetic Regulation

AbstractThe intrinsic polysulfides shuttle, resulting from not only concentration‐gradient diffusion but also slow conversion kinetics of polysulfides, bears the primary responsibility for the poor capacity and cycle stability of lithium–sulfur batteries (LSBs). Here, it is first presented that enriched edge sites derived from vertical standing and ultrathin 2D layered metal selenides (2DLMS) can simultaneously achieve the thermodynamic and kinetic regulation for polysulfides diffusion, which is systematically elucidated through theoretical calculation, electrochemical characterization, and spectroscopic/microscopic analysis. When employed to fabricate compact coating layer of separator, an ultrahigh capacity of 1338.7 mA h g−1 is delivered after 100 cycles at 0.2 C, which is the best among the reports. Over 1000 cycles, the cell still maintains the capacity of 546.8 mA h g−1 at 0.5 C. Moreover, the cell exhibits outstanding capacities of 1106.2 and 865.7 mA h g−1 after 100 cycles at stern temperature of 0 and −25 °C. The superior low‐temperature performance is appealing for extended practical application of LSBs. Especially, in view of the economy, the 2DLMS is recycled as an anode of lithium‐ion and sodium‐ion batteries after finishing the test of LSBs. The low‐cost and scalable 2DLMS with enriched egde sites open a new avenue for the perfect regulation of the sulfur electrode.

Stable and efficient perovskite solar cells fabricated using aqueous lead nitrate precursor: Interpretation of the conversion mechanism and renovation of the sequential deposition

In this study, we renovated the sequential deposition route to fabricate a high-quality methylammonium lead iodide (MAPbI3) capping layer in scaffold-type PSCs from a low-toxicity aqueous lead nitrate precursor system. Through interpretation of the slow and stepwise conversion mechanism from lead nitrate to MAPbI3 in a methylammonium iodide bath, two key innovations, namely chloride inclusion in the methylammonium iodide bath and multiple-cycle immersion, were applied to remedy the flaws in the original MAPbI3 film. The PSC fabricated from the aqueous lead nitrate precursor through this renovated process showed remarkable stability over 55 days in an ambient dark chamber. Our work clearly indicates that using water as a processing solvent is irrelevant to the conversion efficiency or stability of a PSC and demonstrates no difference in the quality of PSC made by PbI2/DMF protocol. This water-processed, environmentally friendly precursor system lights a direction of clean production of PSC using a minimal quantity of harmful organic solvents.

Nonstandard neutrino self-interactions in a supernova and fast flavor conversions

We study the effects of non-standard self-interactions (NSSI) of neutrinos streaming out of a core-collapse supernova. We show that with NSSI, the standard linear stability analysis gives rise to linearly as well as exponentially growing solutions. For a two-box spectrum, we demonstrate analytically that flavor-preserving NSSI lead to a suppression of bipolar collective oscillations. In the intersecting four-beam model, we show that flavor-violating NSSI can lead to fast oscillations even when the angle between the neutrino and antineutrino beams is obtuse, which is forbidden in the Standard Model. This leads to the new possibility of fast oscillations in a two-beam system with opposing neutrino-antineutrino fluxes, even in the absence of any spatial inhomogeneities. Finally, we solve the full non-linear equations of motion in the four-beam model numerically, and explore the interplay of fast and slow flavor conversions in the long-time behavior, in the presence of NSSI.

Stable and Efficient Perovskite Solar Cells Fabricated Using Aqueous Lead Nitrate Precursor: Interpretation of the Conversion Mechanism and Renovation of the Sequential Deposition

In this study, we renovated the sequential deposition route to fabricate a high-quality methylammonium lead iodide (MAPbI3) capping layer in scaffold-type PSCs from a low-toxicity aqueous lead nitrate precursor system. Through interpretation of the slow and stepwise conversion mechanism from lead nitrate to MAPbI3 in a methylammonium iodide bath, two key innovations, namely chloride inclusion in the methylammonium iodide bath and multiple-cycle immersion, were applied to remedy the flaws in the original MAPbI3 film. The PSC fabricated from the aqueous lead nitrate precursor through this renovated process showed remarkable stability over 55 days in an ambient dark chamber. Our work clearly indicates that using water as a processing solvent is irrelevant to the conversion efficiency or stability of a PSC and demonstrates no difference in the quality of PSC made by PbI2/DMF protocol. This water-processed, environmentally friendly precursor system lights a direction of clean production of PSC using a minimal quantity of harmful organic solvents.

In situ insights into the nanoscale deposition of 5,6-dihydroxyindole-based coatings and the implications on the underwater adhesion mechanism of polydopamine coatings.

The biomimetic coating polydopamine (PDA) has emerged as a promising coating material for various applications. However, the mechanism of PDA deposition onto surfaces is not fully understood, and the coating components of PDA and its relation to the putative intermediate 5,6-dihydroxyindole (DHI) are still controversial. This investigation discloses the deposition mechanisms of dopamine (DA)-based coatings and DHI-based coatings onto silicon surfaces by monitoring the nanoscale deposition of both coatings in situ using high-precision ellipsometry. We posit that the rapid and instantaneous nano-deposition of PDA coatings onto silicon surface in the initial stages critically involves the oxidation of DHI and/or its related oligomers. Our studies also show that the slow conversion of DA to DHI in PDA solution and the coupling between DA and DHI-derived precursors could be crucial for subsequent PDA coating growth. These findings elucidate the critical role of DHI, acting as an ‘initiator’ and a ‘cross linker’, in the PDA coating formation. Overall, our study provides important information on the early stage nano-deposition behavior in the construction of PDA coatings and DHI-based coatings.

Modern Examination of Tuberculosis-Diabetes Comorbidity

Tuberculosis-diabetes co-morbidity (TB-DM) has been a hurdle in the elimination of tuberculosis worldwide. Individuals with Type 2 diabetes mellitus (T2DM) can become vulnerable to bacterial infections, due to compromised cell mediated immunity [1, 2]. Therefore, individuals with diabetes are at an increased risk for developing an active tuberculosis (TB) disease when infected with Mycobacterium tuberculosis (Mtb). It is estimated that these individuals with T2DM are about three times more likely to develop the active TB compared to individuals without diabetes. Approximately 10% of all TB cases are linked to diabetes and the risk of death from TB is roughly double for those with diabetes, especially in middle to low-income areas [3, 4]. Patients with both T2DM and TB have worse outcomes, including slower bacteria conversion, lower rate of cure, higher chances to relapse, increased risk of mortality, and even escalated drug resistance. While it is known that diabetes causes immune dysfunction, there are still many questions as to how diabetes worsens TB outcomes. It is reported that diabetes might change the appropriate mechanisms of immunological factors that maintain host immune defenses towards infectious agents, the production of specific cytokines, increased formation of reactive oxygen species, as well as reduced levels of the antioxidant glutathione (GSH). In this review, we explore recent research that helps explain the reasons for tuberculosis-diabetes (TB-DM) comorbidity as well as the possible causes for the increased risk of mortality and finally possible prophylactic treatments.

Constitutively Active SMAD2/3 Are Broad-Scope Potentiators of Transcription-Factor-Mediated Cellular Reprogramming

SummaryReprogramming of cellular identity using exogenous expression of transcription factors (TFs) is a powerful and exciting tool for tissue engineering, disease modeling, and regenerative medicine. However, generation of desired cell types using this approach is often plagued by inefficiency, slow conversion, and an inability to produce mature functional cells. Here, we show that expression of constitutively active SMAD2/3 significantly improves the efficiency of induced pluripotent stem cell (iPSC) generation by the Yamanaka factors. Mechanistically, SMAD3 interacts with reprogramming factors and co-activators and co-occupies OCT4 target loci during reprogramming. Unexpectedly, active SMAD2/3 also markedly enhances three other TF-mediated direct reprogramming conversions, from B cells to macrophages, myoblasts to adipocytes, and human fibroblasts to neurons, highlighting broad and general roles for SMAD2/3 as cell-reprogramming potentiators. Our results suggest that co-expression of active SMAD2/3 could enhance multiple types of TF-based cell identity conversion and therefore be a powerful tool for cellular engineering.

Self-Assembly Pathways of β-Sheet-Rich Amyloid-β(1-40) Dimers: Markov State Model Analysis on Millisecond Hybrid-Resolution Simulations.

Early oligomerization during amyloid-β (Aβ) aggregation is essential for Aβ neurotoxicity. Understanding how unstructured Aβs assemble into oligomers, especially those rich in β-sheets, is essential but remains challenging as the assembly process is too transient for experimental characterization and too slow for molecular dynamics simulations. So far, atomic simulations are limited only to studies of either oligomer structures or assembly pathways for short Aβ segments. To overcome the computational challenge, we combine in this study a hybrid-resolution model and adaptive sampling techniques to perform over 2.7 ms of simulations of formation of full-length Aβ40 dimers that are the earliest toxic oligomeric species. The Markov state model is further employed to characterize the transition pathways and associated kinetics. Our results show that for two major forms of β-sheet-rich structures reported experimentally, the corresponding assembly mechanisms are markedly different. Hairpin-containing structures are formed by direct binding of soluble Aβ in β-hairpin-like conformations. Formation of parallel, in-register structures resembling fibrils occurs ∼100-fold more slowly and involves a rapid encounter of Aβ in arbitrary conformations followed by a slow structural conversion. The structural conversion proceeds via diverse pathways but always requires transient unfolding of encounter complexes. We find that the transition kinetics could be affected differently by intra-/intermolecular interactions involving individual residues in a conformation-dependent manner. In particular, the interactions involving Aβ's N-terminal part promote the assembly into hairpin-containing structures but delay the formation of fibril-like structures, thus explaining puzzling observations reported previously regarding the roles of this region in the early assembly process.

Effect of Ticagrerol versus Clopidogrel on Oxidative Stress Bio-markers in Patients with Chronic Stable Angina after Percutaneous Coronary Intervention

Background: Ischemic heart disease remains the leading cause of death in both developed and under developed countries. The use of antiplatelet drugs specifically the thienopyridine has become a standard for the treatment of acute coronary syndrome. These drugs irreversibly inhibit the platelet aggregation by blocking the P2Y12 receptor. But currently this therapeutic choice has become limited due to potential interaction with other drugs, slow hepatic conversion, genetic resistance and narrow therapeutic safety margin. Ticagrerol, a reversible P2Y12 receptor inhibitor may represent a significant advancement over currently available oral antiplatelet drugs.Objectives: The study was intended to compare the effect of Ticagrelor and Clopidogrel on oxidative stress markers in patients of chronic stable angina (CSA) following percutaneous coronary intervention (PCI).Materials & Methods: The present prospective observational study was carried out in the Department of Pharmacology, Cardiology and Microbiology, BSMMU, Dhaka from September 2014 to February 2016. The study included a total of 100 CSA patients. Patients were divided into two groups, Ticagrelor and Clopidogrel treated groups (each having 50 patients). The baseline laboratory parameters-Malondihyde (MDA), Reduced glutathione (GSH), bleeding time, clotting time and platelet count, were measured and then patients of both groups underwent PCI. The same parameters were again assessed at follow up after 4 weeks of intervention. Total 12 patients from Ticagrelor and 14 patients from Clopidogrel groups were dropped out. Comparisons of the laboratory parameters were made between two groups at baseline and at follow up and also within group before and after intervention.Result: In the present study at baseline characteristics of patients treated with ticagrelor and clopidogrel were almost identical in terms of age, sex, diabetes and hypertension. The level of plasma MDA in ticagrelor group was significantly reduced from baseline to follow up(4.5 ± 1.8 to 1.4 ± 0.7, p <0.001) and in clopidogrel group (4.2 ± 1.2 to 1.3 ± 0.7, p <0.001). GSH level was increased from 0.7 mg/dl to 2.5 mg/dl (p <0.001) in ticagrerol group and in clopidogrel group 0.6 mg/dl to 1.4 mg/dl, p <0.001).Conclusion: The study concluded that both ticagrelor and clopidogrel are similar effect on oxidative stress markers, resulting from oxidative injury processes in patients of chronic stable angina.University Heart Journal Vol. 12, No. 1, January 2016; 26-30

Photoswitchable Dihydroazulene Macrocycles for Solar Energy Storage: The Effects of Ring Strain.

Efficient energy storage and release are two major challenges of solar energy harvesting technologies. The development of molecular solar thermal systems presents one approach to address these issues by tuning the isomerization reactions of photo/thermoswitches. Here we show that the incorporation of photoswitches into macrocyclic structures is a particularly attractive solution for increasing the storage time. We present the synthesis and properties of a series of macrocycles incorporating two dihydroazulene (DHA) photoswitching subunits, bridged by linkers of varying chain length. Independent of ring size, all macrocycles exhibit stepwise, light-induced, ring-opening reactions (DHA-DHA to DHA-VHF to VHF-VHF; VHF = vinylheptafulvene) with the first DHA undergoing isomerization with a similar efficiency as the uncyclized parent system while the second (DHA-VHF to VHF-VHF) is significantly slower. The energy-releasing, VHF-to-DHA, ring closures also occur in a stepwise manner and are systematically found to proceed slower in the more strained (smaller) cycles, but in all cases with a remarkably slow conversion of the second VHF to DHA. We managed to increase the half-life of the second VHF-to-DHA conversion from 65 to 202 h at room temperature by simply decreasing the ring size. A computational study reveals the smallest macrocycle to have the most energetic VHF-VHF state and hence highest energy density.

Structure of C-terminal Domain of Peptidyl-prolyl cis-trans Isomerase from Pseudomonas syringae pv. Tomato str. DC3000 at 1.6Å Resolution.

Peptidyl-prolyl cis-trans isomerase (PPIase) accelerates the intrinsically slow conversion between cis- and trans- configurations of proline, thus affecting backbone conformation and altering the direction of peptide chains. PPIase from Pseudomonas syringae pv. Tomato (PSPTO) DC3000 (PSPTO-PPIase) is considered to belong to the FKBP subfamily of PPIase. To solve the high resolution structure of the PSPTO-PPIase, and to explore its potential function in plants pathogen PSPTO DC3000. The PSPTO-PPIase was expressed in E.coli and purified through ion exchange and size exclusion chromatography. While only the C-terminal domain of PSPTO-PPIase was successfully crystalized, and its structure was solved to 1.6 Å resolution by molecular replacement method. Structural comparison showed that PSPTO-PPIase adopts a similar overall fold with microphage infectivity potentiators (MIPs), which also belong to the FKBP subfamily of PPIase. In addition, the BIAcore result confirmed that PSPTO-PPIase can bind an immunosuppressive drug FK506 as some other FKBP subfamily members do. Our results suggested that PSPTO-PPIase may function in a similar manner to virulent factor MIPs during pathogenesis. And the immunosuppressive drugs FK506 and rapamycin binding to PSPTO-PPIase potentially interferes and inhibits the plant pathogen PSPTO DC3000. In addition, the amino acids with short side chains in the fourth loop (L4) of PSPTO-PPIase may account for its variable roles in the respective pathogen.

Enzyme-Mediated Conversion of Flavin Adenine Dinucleotide (FAD) to 8-Formyl FAD in Formate Oxidase Results in a Modified Cofactor with Enhanced Catalytic Properties.

Flavins, including flavin adenine dinucleotide (FAD), are fundamental catalytic cofactors that are responsible for the redox functionality of a diverse set of proteins. Alternatively, modified flavin analogues are rarely found in nature as their incorporation typically results in inactivation of flavoproteins, thus leading to the disruption of important cellular pathways. Here, we report that the fungal flavoenzyme formate oxidase (FOX) catalyzes the slow conversion of noncovalently bound FAD to 8-formyl FAD and that this conversion results in a nearly 10-fold increase in formate oxidase activity. Although the presence of an enzyme-bound 8-formyl FMN has been reported previously as a result of site-directed mutagenesis studies of lactate oxidase, FOX is the first reported case of 8-formyl FAD in a wild-type enzyme. Therefore, the formation of the 8-formyl FAD cofactor in formate oxidase was investigated using steady-state kinetics, site-directed mutagenesis, ultraviolet-visible, circular dichroism, and fluorescence spectroscopy, liquid chromatography with mass spectrometry, and computational analysis. Surprisingly, the results from these studies indicate not only that 8-formyl FAD forms spontaneously and results in the active form of FOX but also that its autocatalytic formation is dependent on a nearby arginine residue, R87. Thus, this work describes a new enzyme cofactor and provides insight into the little-understood mechanism of enzyme-mediated 8α-flavin modifications.

Compost-derived humic acids as regulators for reductive degradation of nitrobenzene

Nitrobenzene (NB) is a major class of contaminants in soil and groundwater. The current methods involved in the reductive degradation of NB suffer either cost-ineffective or slow conversion rate. Here, we investigated the mechanisms regarding compost-derived humic acids (HAs) as cost-effective regulators to enhance the reduction of NB to aniline (AN). Our results show that the compost-derived HAs, which have been reduced by a Pd-H2 catalytic system, were able to reduce NB to AN, and their redox properties were the main factors governing the reduction of NB to AN. The decreasing reduction of NB was mainly caused by the decreasing phenol content of compost-derived HAs during composting. In addition, the results reveal that the increase in the generation content of AN was mainly attributed to the increase in the quinones, aromaticity and humic-like components of compost-derived HAs. The findings demonstrate that the HAs derived from compost are effective regulators to enhance the reduction of NB to AN, and that they exert a bright application prospect for the remediation of the NB-contaminated soil.

Barkhausen noise probe of the ferroelectric transition in the relaxor PbMg1/3Nb2/3O3−12%PbTiO3

Barkhausen current noise is used to probe the slow field-driven conversion of the glassy relaxor ferroelectric state to an ordered ferroelectric (FE) state. The frequent presence of distinct micron-scale Barkhausen events well before the polarization current starts to speed up shows that the process is not a conventional nucleation-limited one. The prevalence of reverse switching events near the onset of the rapid part of the transition strongly indicates that electric dipole interactions play a key role. The combination of Barkhausen noise changes and changes in the complex dielectric response indicate that the process consists of an initial mixed-alignment domain formation stage followed by growth of the domains aligned with the applied field.

Identification of Nitration Products during Heterogeneous Reaction of NO2 on Soot in the Dark and under Simulated Sunlight.

Author: The present work, involving the formation of NO and nitrous acid (HONO) and the nitration of polycyclic aromatic hydrocarbon (PAHs) to nitro-PAHs as well as the uptake coefficients of NO2, has been performed on a normal-pressure flow reactor to identify the nitration products during the heterogeneous reaction of soot toward NO2 in the dark and under simulated sunlight. Two types of soot particles, namely the commercial black carbon (BC) and the diesel engine soot (ES), were selected as the studied soot to compare the impacts of soot properties on heterogeneous nitration. During the whole reaction on either of the two studied soots in the dark, a fast reversible physical adsorption is observed at the very beginning, followed by a slow irreversible chemical conversion from NO2 to HONO and NO, in good agreement with the "reduction-oxidation" mechanism. HONO is the most abundant product during the nitration reaction on the two studied soots, contributing to 70-90% of consumed NO2 after 50 min exposure. Reaction orders of NO2 for HONO are determined as 1.20 ± 0.07 and 1.31 ± 0.04 for BC and ES, respectively, which are both close to first-order. Moreover, four sorts of PAHs compounds and their five nitro-derivatives have been identified and quantified during the reaction. About 40% and 20% of the total four measured PAHs are consumed on BC and ES, respectively, resulting in an increase in the total five measured nitro-PAHs by 21-fold on BC and 2.8-fold on ES. Finally, the impacts of light on gaseous and organics products have been investigated and the results confirm that simulated sunlight can enhance the reactivity of PAHs toward NO2 and cause the photolysis of newly formed nitro-compounds with more HONO formation, strongly suggesting that photochemistry of soot in the presence of NO2 is of great importance to be a photochemical source of HONO and would also influence the fates of PAHs and nitro-PAHs on soot.