Locking the Ultrasound-Induced Active Conformation of Metalloenzymes in Metal-Organic Frameworks.

Enhancing the enzymatic activity inside metal-organic frameworks (MOFs) is a critical challenge in chemical technology and bio-technology, which, if addressed, will broaden their scope in energy, food, environmental, and pharmaceutical industries. Here, we report a simple yet versatile and effective strategy to optimize biocatalytic activity by using MOFs to rapidly "lock" the ultrasound (US)-activated but more fragile conformation of metalloenzymes. The results demonstrate that up to 5.3-fold and 9.3-fold biocatalytic activity enhancement of the free and MOF-immobilized enzymes could be achieved compared to those without US pretreatment, respectively. Using horseradish peroxidase as a model, molecular dynamics simulation demonstrates that the improved activity of the enzyme is driven by an opened gate conformation of the heme active site, which allows more efficient substrate binding to the enzyme. The intact heme active site is confirmed by solid-state UV-vis and electron paramagnetic resonance, while the US-induced enzyme conformation change is confirmed by circular dichroism spectroscopy and Fourier-transform infrared spectroscopy. In addition, the improved activity of the biocomposites does not compromise their stability upon heating or exposure to organic solvent and a digestion cocktail. This rapid locking and immobilization strategy of the US-induced active enzyme conformation in MOFs gives rise to new possibilities for the exploitation of highly efficient biocatalysts for diverse applications.

Deletion of Methionine Sulfoxide Reductase A Does Not Affect Atherothrombosis but Promotes Neointimal Hyperplasia and Extracellular Signal-Regulated Kinase 1/2 Signaling.

OBJECTIVE: Emerging evidence suggests that methionine oxidation can directly affect protein function and may be linked to cardiovascular disease. The objective of this study was to define the role of the methionine sulfoxide reductase A (MsrA) in models of vascular disease and identify its signaling pathways. APPROACH AND RESULTS: MsrA was readily identified in all layers of the vascular wall in human and murine arteries. Deletion of the MsrA gene did not affect atherosclerotic lesion area in apolipoprotein E-deficient mice and had no significant effect on susceptibility to experimental thrombosis after photochemical injury. In contrast, the neointimal area after vascular injury caused by complete ligation of the common carotid artery was significantly greater in MsrA-deficient than in control mice. In aortic vascular smooth muscle cells lacking MsrA, cell proliferation was significantly increased because of accelerated G1/S transition. In parallel, cyclin D1 protein and cdk4/cyclin D1 complex formation and activity were increased in MsrA-deficient vascular smooth muscle cell, leading to enhanced retinoblastoma protein phosphorylation and transcription of E2F. Finally, MsrA-deficient vascular smooth muscle cell exhibited greater activation of extracellular signal-regulated kinase 1/2 that was caused by increased activity of the Ras/Raf/mitogen-activated protein kinase signaling pathway. CONCLUSIONS: Our findings implicate MsrA as a negative regulator of vascular smooth muscle cell proliferation and neointimal hyperplasia after vascular injury through control of the Ras/Raf/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase 1/2 signaling pathway.

Nanoscale Titanium Surface Engineering via Low-Temperature Hydrothermal Etching for Enhanced Antimicrobial Properties.

Bioinspired nanotopography artificially fabricated on titanium surfaces offers a solution for the rising issue of postoperative infections within orthopedics. On a small scale, hydrothermal etching has proven to deliver an effective antimicrobial nanospike surface. However, translation to an industrial setting is limited by the elevated synthesis temperature (150 °C) and associated equipment requirements. Here, for the first time, we fabricate surface nanostructures using comparatively milder synthesis temperatures (75 °C), which deliver physicochemical properties and antimicrobial capability comparable to the high-temperature surface. Using a KOH etchant, the simultaneous formation of titania and titanate crystals at both temperatures produces a one-dimensional nanostructure array. Analysis indicated that the formation mechanism comprises dissolution and reprecipitation processes, identifying the deposited titanates as hydrated layered tetra-titanates (K2Ti4O9·nH2O). A proposed nanospike formation mechanism was confirmed through the identification of a core and outer shell for individual nanostructures, primarily comprised of titanates and titania, respectively. Etching conditions dictated crystalline formation, favoring a thicker titanate core for nanorods under higher synthesis temperatures and etchant concentrations. A bactericidal investigation showed the efficacy against Gram-negative bacteria for a representative low-temperature nanosurface (34.4 ± 14.4%) was comparable to the higher temperature nanosurface (34.0 ± 17.0%), illustrating the potential of low-temperature hydrothermal synthesis. Our results provide valuable insight into the applicability of low-temperature etching protocols that are more favorable in large-scale manufacturing settings.

Defect-Promoted Ni-Based Layer Double Hydroxides with Enhanced Deprotonation Capability for Efficient Biomass Electrooxidation.

Ni-based hydroxides are promising electrocatalysts for biomass oxidation reactions, supplanting the oxygen evolution reaction (OER) due to lower overpotentials while producing value-added chemicals. The identification and subsequent engineering of their catalytically active sites are essential to facilitate these anodic reactions. Herein, the proportional relationship between catalysts' deprotonation propensity and Faradic efficiency of 5-hydroxymethylfurfural (5-HMF)-to-2,5 furandicarboxylic acid (FDCA, FEFDCA ) is revealed by thorough density functional theory (DFT) simulations and atomic-scale characterizations, including in situ synchrotron diffraction and spectroscopy methods. The deprotonation capability of ultrathin layer-double hydroxides (UT-LDHs) is regulated by tuning the covalency of metal (M)-oxygen (O) motifs through defect site engineering and selection of M3+ co-chemistry. NiMn UT-LDHs show an ultrahigh FEFDCA of 99% at 1.37 V versus reversible hydrogen electrode (RHE) and retain a high FEFDCA of 92.7% in the OER-operating window at 1.52 V, about 2× that of NiFe UT-LDHs (49.5%) at 1.52 V. Ni-O and Mn-O motifs function as dual active sites for HMF electrooxidation, where the continuous deprotonation of Mn-OH sites plays a dominant role in achieving high selectivity while suppressing OER at high potentials. The results showcase a universal concept of modulating competing anodic reactions in aqueous biomass electrolysis by electronically engineering the deprotonation behavior of metal hydroxides, anticipated to be translatable across various biomass substrates.

The multifunctional Ca2+/calmodulin-dependent kinase II regulates vascular smooth muscle migration through matrix metalloproteinase 9.

The multifunctional CaMKII has been implicated in vascular smooth muscle cell (VSMC) migration, but little is known regarding its downstream targets that mediate migration. Here, we examined whether CaMKII regulates migration through modulation of matrix metalloproteinase 9 (MMP9). Using CaMKIIδ(-/-) mice as a model system, we evaluated migration and MMP9 regulation in vitro and in vivo. After ligation of the common carotid artery, CaMKII was activated in the neointima as determined by oxidation and autophosphorylation. We found that MMP9 was robustly expressed in the neointima and adventitia of carotid-ligated wild-type (WT) mice but was barely detectable in CaMKIIδ(-/-) mice. The perimeter of the external elastic lamina, a correlate of migration-related outward remodeling, was increased in WT but not in CaMKIIδ(-/-) mice. Migration induced by serum, platelet-derived growth factor, and tumor necrosis factor-α (TNF-α) was significantly decreased in CaMKIIδ(-/-) as compared with WT VSMCs, but migration was rescued with adenoviral overexpression of MMP9 in CaMKIIδ(-/-) VSMCs. Likewise, overexpression of CaMKIIδ in CaMKIIδ(-/-) VSMCs increased migration, whereas an oxidation-resistant mutant of CaMKIIδ did not. TNF-α strongly induced CaMKII oxidation and autophosphorylation as well as MMP9 activity, mRNA, and protein levels in WT, but not in CaMKIIδ(-/-) VSMC. Surprisingly, TNF-α strongly induced MMP9 promoter activity in WT and CaMKIIδ(-/-) VSMC. However, the MMP9 mRNA stability was significantly decreased in CaMKIIδ(-/-) VSMC. Our data demonstrate that CaMKII promotes VSMC migration through posttranscriptional regulation of MMP9 and suggest that CaMKII effects on MMP9 expression may be a therapeutic pathway in vascular injury.

Optimization of a Pyrimidinone Series for Selective Inhibition of Ca2+/Calmodulin-Stimulated Adenylyl Cyclase 1 Activity for the Treatment of Chronic Pain.

Adenylyl cyclase type 1 (AC1) is involved in signaling for chronic pain sensitization in the central nervous system and is an emerging target for the treatment of chronic pain. AC1 and a closely related isoform AC8 are also implicated to have roles in learning and memory signaling processes. Our team has carried out cellular screening for inhibitors of AC1 yielding a pyrazolyl-pyrimidinone scaffold with low micromolar potency against AC1 and selectivity versus AC8. Structure-activity relationship (SAR) studies led to analogues with cellular IC50 values as low as 0.25 µM, selectivity versus AC8 and other AC isoforms as well as other common neurological targets. A representative analogue displayed modest antiallodynic effects in a mouse model of inflammatory pain. This series represents the most potent and selective inhibitors of Ca2+/calmodulin-stimulated AC1 activity to date with improved drug-like physicochemical properties making them potential lead compounds for the treatment of inflammatory pain.

Low Temperature Nano Mechano-electrocatalytic CH4 Conversion.

Transforming natural resources to energy sources, such as converting CH4 to H2 and carbon, at high efficiency and low cost is crucial for many industries and environmental sustainability. The high temperature requirement of CH4 conversion regarding many of the current methods remains a critical bottleneck for their practical uptake. Here we report an approach based on gallium (Ga) liquid metal droplets, Ni(OH)2 cocatalysts, and mechanical energy input that offers low-temperature and scalable CH4 conversion into H2 and carbon. Mainly driven by the triboelectric voltage, originating from the joint contributions of the cocatalysts during agitation, CH4 is converted at the Ga and Ni(OH)2 interface through nanotribo-electrochemical reaction pathways. The efficiency of the system is enhanced when the reaction is performed at an increased pressure. The dehydrogenation of other nongaseous hydrocarbons using this approach is also demonstrated. This technology presents a possible low energy route for CH4 conversion without involving high temperature and harsh operating conditions.

Valence Alignment of Mixed Ni-Fe Hydroxide Electrocatalysts through Preferential Templating on Graphene Edges for Enhanced Oxygen Evolution.

Engineering the metal-carbon heterointerface has become an increasingly important route toward achieving cost-effective and high-performing electrocatalysts. The specific properties of graphene edge sites, such as the high available density of states and extended unpaired π-bonding, make it a promising candidate to tune the electronic properties of metal catalysts. However, to date, understanding and leveraging graphene edge-metal catalysts for improved electrocatalytic performance remains largely elusive. Herein, edge-rich vertical graphene (er-VG) was synthesized and used as a catalyst support for Ni-Fe hydroxides for the oxygen evolution reaction (OER). The hybrid Ni-Fe/er-VG catalyst exhibits excellent OER performance with a mass current of 4051 A g-1 (at overpotential η = 300 mV) and turnover frequency (TOF) of 4.8 s-1 (η = 400 mV), outperforming Ni-Fe deposited on pristine VG and other metal foam supports. Angle-dependent X-ray absorption spectroscopy shows that the edge-rich VG support can preferentially template Fe-O units with a specific valence orbital alignment interacting with the unoccupied density of states on the graphene edges. This graphene edge-metal interaction was shown to facilitate the formation of undersaturated and strained Fe-sites with high valence states, while promoting the formation of redox-activated Ni species, thus improving OER performance. These findings demonstrate rational design of the graphene edge-metal interface in electrocatalysts which can be used for various energy conversion and chemical synthesis reactions.

Oil dispersion increases the apparent bioavailability and toxicity of diesel to rainbow trout (Oncorhynchus mykiss).

Diesel is a complex mixture containing polycyclic aromatic hydrocarbons, which persist after a spill, pass readily from water into tissues, and are toxic to early life stages of fish. The bioavailability and chronic toxicity of hydrocarbons dissolved into water from floating diesel (water-accommodated fraction) and chemically dispersed diesel (chemically enhanced water-accommodated fraction) were measured by the extent of ethoxyresorufin-O-deethylase (EROD) induction in juvenile rainbow trout (Oncorhynchus mykiss) and by the severity of blue sac disease in embryos. The water-accommodated fraction of floating diesel was virtually nontoxic to embryos at nominal concentrations up to 1,000 mg/L, causing only small weight changes. Liver EROD induction in juvenile trout was only observed at the highest nominal water-accommodated fraction concentration (10,000 mg/L). Chemical dispersion increased the bioavailability and toxicity of diesel to trout by 100-fold. Diesel chemically enhanced water-accommodated fraction induced EROD activity, caused blue sac disease, and impaired development and growth of embryonic trout at nominal concentrations as low as 10 mg/L; 88% mortality occurred at 100 mg/L. However, when total hydrocarbon concentrations were measured, differences between dispersed and undispersed diesel disappeared, with a median lethal concentration of 8 mg/L of total hydrocarbons and sublethal median effective concentrations ranging from 1.3 to 6.1 mg/L. Dispersion of diesel by high-energy mechanical mixing was recently reported to cause acute lethality to juvenile trout between 40 and 200 mg/L. Therefore, dispersion of oil by any means increases the bioavailability and apparent toxicity of diesel to fish embryos without changing the toxicity of its components. Nevertheless, in an actual spill, dispersion of diesel increases the effects of oil on fish populations.

Embryotoxicity of retene in cotreatment with 2-aminoanthracene, a cytochrome P4501A inhibitor, in rainbow trout (Oncorhynchus mykiss).

Environmentally relevant mixtures of polycyclic aromatic hydrocarbons (PAHs; e.g., crude oils) are often rich in alkyl-PAHs, such as retene (7-isopropyl-1-methylphenanthrene), which produce dioxin-like toxicity in fish embryos. The mechanism of alkyl-PAH toxicity is not well understood but was previously thought to be mediated by cytochrome P4501A (CYPIA) enzymes. To understand the role of CYP1A in retene toxicity, we coexposed free-swimming rainbow trout (Oncorhynchus mykiss) embryos to 100 microg/L of retene and to a range of concentrations of 2-aminoanthracene (2AA; a known CYP1A inhibitor). Ethoxyresorufin-O-deethylase (EROD) assays of juvenile trout coexposed to 2AA and retene confirmed that 2AA inhibited CYP1A (median inhibitory concentration [IC50] for 2AA, 62 microg/L). In two independent trials, 2AA, both alone and in cotreatment with retene, produced a concentration-dependent increase in toxicity to embryonic trout. The toxicity resulting from 2AA alone is, to our knowledge, the first reported for embryonic stages of fish, with median lethal concentrations (LC50s) of 19 and 125 microg/L and overall sublethal median effective concentrations (EC50s) of 17 and 38 microg/L. Toxicity increased in embryos coexposed to retene and 2AA, resulting in LC50s of 14 and 17 microg/L of 2AA and overall EC50s of 7 and 3 microg/L of 2AA. The exposure-response curves for 2AA alone and for 2AA with retene were parallel, suggesting a common mode of action between the two treatment regimes and between retene and 2AA. Taken together with the juvenile EROD data, the toxicity of 2AA alone and in cotreatment with retene may be EROD (CYP1A) independent. The mixture toxicity was not consistent with previous coexposures to CYP1A inducers and inhibitors, suggesting that the current risk assessment model may not be a good predictor of PAH mixture toxicity.

The role of iron in hexavalent chromium reduction by municipal landfill leachate.

The function of iron (ferric (Fe(III)) and ferrous (Fe(II))) in the hexavalent chromium (Cr(VI)) reduction mechanism by bacteria in municipal landfill leachate (MLL) was assessed. Evidence of an "electron shuttle" mechanism was observed, whereby the Cr(VI) was reduced to trivalent chromium (Cr(III)) by Fe(II) with the resulting Fe(III) bacterially re-reduced to Fe(II). Typically, investigations on this electron shuttle mechanism have been performed in an artificial medium. As MLL comprises an elaborate mixture of bacteria, humic materials and organic and inorganic species, additional complexities were evident within the cycle in this study. Bioavailability of the Fe(III) for bacterial reduction, availability of bacterially produced Fe(II) for chemical Cr(VI) reduction and hydrolysis of Fe(II) and Fe(III) become prevalent during each phase of the shuttle cycle when MLL is present. Each of these factors contributes to the overall rate of bacterial Cr(VI) reduction in this media. This work highlights the need to consider local environmental conditions when assessing the bacterial reduction of Cr(VI).

Evidence for multiple mechanisms of toxicity in larval rainbow trout (Oncorhynchus mykiss) co-treated with retene and alpha-naphthoflavone.

Alkylated polycyclic aromatic hydrocarbons, such as retene (7-isopropyl-1-methylphenanthrene), induce cytochrome P450 1A (CYP1A) enzymes and produce dioxin-like toxicity in the embryo-larval stages of fish characterized by the signs of blue sac disease (BSD). The signs of toxicity are well characterized; however, the mechanism is not well understood. To elucidate the role of CYP1A in retene toxicity, larval rainbow trout (Oncorhynchus mykiss) were co-treated with a range of concentrations of alpha-naphthoflavone (ANF), a known CYP1A inhibitor. The co-treatment produced synergistic toxicity at 3.2-100 microg/L ANF, after which toxicity at 180 microg/L ANF dropped to levels typical of retene-only. At 320 microg/L ANF, toxicity increased with or without retene, indicating that ANF alone was capable of inducing BSD. In addition, the additive toxicity of retene-only and 320 microg/L ANF-only approximately equalled that of the co-exposed larvae (100 microg/L retene+320 microg/L ANF), indicating response addition. Thus, two mechanisms of action occurred in co-exposed larvae at different concentrations of ANF. In trout larvae, there was a correlation between toxicity and CYP1A protein concentrations, and in juvenile trout, ANF produced a concentration-dependent inhibition of ethoxyresorufin-O-deethylase (EROD) activity without a measurable drop in CYP1A protein. Taken together, the mechanism underlying the synergistic toxicity is EROD-independent and may be AhR-dependent. This study demonstrated that multiple, exposure-dependent mechanisms can occur in mixture toxicity, suggesting that current risk assessment models may drastically underestimate toxicity, particularly of mixtures containing both CYP1A inducers and inhibitors.

Microbial reduction of hexavalent chromium by landfill leachate.

The reduction of hexavalent chromium (Cr(VI)) in municipal landfill leachates (MLL) and a non-putrescible landfill leachate (NPLL) was investigated. Complete Cr(VI) reduction was achieved within 17 days in a MLL when spiked with 100 mg l(-1) Cr(VI) or less. In the same period, negligible Cr(VI) reduction was observed in NPLL. In MLL, Cr(VI) reduction was demonstrated to be a function of initial Cr(VI) concentration and bacterial biomass and organic matter concentrations. The bacteria were observed to tolerate 250 mg l(-1) Cr(VI) in MLL and had an optimal growth activity at pH 7.4 in a growth medium. The MLL also possessed an ability to sequentially reduce Cr(VI) over three consecutive spiking cycles.

Endothelial CaMKII as a regulator of eNOS activity and NO-mediated vasoreactivity.

The multifunctional Ca2+/calmodulin-dependent protein kinase II (CaMKII) is a serine/threonine kinase important in transducing intracellular Ca2+ signals. While in vitro data regarding the role of CaMKII in the regulation of endothelial nitric oxide synthase (eNOS) are contradictory, its role in endothelial function in vivo remains unknown. Using two novel transgenic models to express CaMKII inhibitor peptides selectively in endothelium, we examined the effect of CaMKII on eNOS activation, NO production, vasomotor tone and blood pressure. Under baseline conditions, CaMKII activation was low in the aortic wall. Consistently, systolic and diastolic blood pressure, heart rate and plasma NO levels were unaltered by endothelial CaMKII inhibition. Moreover, endothelial CaMKII inhibition had no significant effect on NO-dependent vasodilation. These results were confirmed in studies of aortic rings transduced with adenovirus expressing a CaMKII inhibitor peptide. In cultured endothelial cells, bradykinin treatment produced the anticipated rapid influx of Ca2+ and transient CaMKII and eNOS activation, whereas CaMKII inhibition blocked eNOS phosphorylation on Ser-1179 and dephosphorylation at Thr-497. Ca2+/CaM binding to eNOS and resultant NO production in vitro were decreased under CaMKII inhibition. Our results demonstrate that CaMKII plays an important role in transient bradykinin-driven eNOS activation in vitro, but does not regulate NO production, vasorelaxation or blood pressure in vivo under baseline conditions.

The pronociceptive effect of ondansetron in the setting of P-glycoprotein inhibition.

Ondansetron is a potent antiemetic drug that acts through inhibition of the 5HT3 receptors for serotonin. Minimum alveolar concentration (MAC) for isoflurane is not affected by systemic ondansetron; however ondansetron is a substrate of P-glycoprotein, a transport pump expressed in the blood-brain barrier. Thus, we hypothesized that central nervous system concentrations of ondansetron might be reduced by the P-gp protein. As potent inhibitors of P-gp are in clinical trials to improve access of desirable chemotherapeutic and antibiotic drugs to the central nervous system, we studied the effect of ondansetron in the absence of extrusion by P-gp. Normal rats were given lumbar intrathecal ondansetron or vehicle. P-gp knockout mice and wild-type controls were treated with systemic ondansetron in the presence and absence of clinically used P-gp inhibitors. Nociception was assessed as thermal hindpaw withdrawal latency and immobility was assessed as isoflurane MAC. In rats, intrathecal ondansetron (20 g) increased thermal pain sensitivity by 20.0% +/- 5.8% (P < 0.01). Systemic ondansetron (2 mg/kg) increased pain sensitivity in P-gp knockout mice but had no effect in wild-type mice (P < 0.01). Systemic ondansetron had a small but statistically significant pronociceptive effect after treatment of wild-type mice with the P-gp inhibitor quinidine but not with cyclosporine or verapamil. Isoflurane MAC was not changed by intrathecal ondansetron in rats or systemically administered ondansetron in P-gp knockout mice. Intrathecal ondansetron can enhance thermal pain sensitivity. In the absence of P-gp protein, ondansetron can reach concentrations sufficient to increase pain sensitivity. Even with direct spinal application, ondansetron does not alter isoflurane MAC, supporting the idea that 5HT3 modulation does not play a role in general anesthetic immobility.

Retene causes multifunctional transcriptomic changes in the heart of rainbow trout (Oncorhynchus mykiss) embryos.

Fish are particularly sensitive to aryl hydrocarbon receptor (AhR)-mediated developmental toxicity. The molecular mechanisms behind these adverse effects have remained largely unresolved in salmonids, and for AhR-agonistic polycyclic aromatic hydrocarbons (PAHs). This study explored the cardiac transcriptome of rainbow trout (Oncorhynchus mykiss) eleuteroembryos exposed to retene, an AhR-agonistic PAH. The embryos were exposed to retene (nominal concentration 32 µg/L) and control, their hearts were collected before, at and after the onset of the visible signs of developmental toxicity, and transcriptomic changes were studied by microarray analysis. Retene up- or down-regulated 122 genes. The largest Gene Ontology groups were signal transduction, transcription, apoptosis, cell growth, cytoskeleton, cell adhesion/mobility, cardiovascular development, xenobiotic metabolism, protein metabolism, lipid metabolism and transport, and amino acid metabolism. Together these findings suggest that retene affects multiple signaling cascades in the heart of rainbow trout embryos, and potentially disturbs processes related to cardiovascular development and function.

Modelling the leaching of Pb, Cd, As, and Cr from cementitious waste using PHREEQC.

A leaching model was developed using the United States Geological Survey public domain PHREEQC geochemical package to simulate the leaching of Pb, Cd, As, and Cr from cementitious wastes. The model utilises both kinetic terms and equilibrium thermodynamics of key compounds and provides information on leachate and precipitate speciation. The model was able to predict the leaching of Pb, Cd, As, and Cr from cement in the presence of both simple (0.1 and 0.6M acetic acid) and complex municipal landfill leachates. Heavy metal complexation by the municipal landfill leachate was accounted for by the introduction of a monoprotic organic species into the model. The model indicated Pb and As were predominantly incorporated within the calcium silicate hydrate matrix while a greater portion of Cd was seen to exist as discrete particles in the cement pores and Cr (VI) existed mostly as free CrO4(2-) ions. Precipitation was found to be the dominant mechanism controlling heavy metal solubility with carbonate and silicate species governing the solubility of Pb and carbonate, silicate and hydroxide species governing the solubility of Cd. In the presence of acetic acid, at low pH values Pb and Cd acetate complexes were predominant whereas, at high pH values, hydroxide species dominated. At high pH values, the concentration of As in the leachate was governed by the solubility of Ca3(AsO4)2 with the presence of carbonate alkalinity competing with arsenate for Ca ions. In the presence of municipal landfill leachate, Pb and Cd organic complexes dominated the heavy metal species in solution. The reduction of As and Cr in municipal landfill leachate was crucial for determining aqueous speciation, with typical municipal landfill conditions providing the reduced forms of As and Cr.

Evaluating the applicability of regulatory leaching tests for assessing the hazards of Pb-contaminated soils.

Soil contamination is a major environmental problem due to the ecological threat it poses. In this work, electron probe microanalysis (EPMA), X-ray diffraction (XRD), and leaching studies were employed to explain the different leaching behaviors of non-stabilized and stabilized soils. The applicability of the leaching fluids used in the toxicity characteristic leaching procedure (TCLP) and Australian Standards, AS 4439.1-1997 for assessing the hazards of contaminated soils was investigated as was the leaching of lead from soil stabilized by cement and buffered phosphate techniques. The results showed Pb speciation in the soil highly influenced metal leaching. The synthetic leaching fluids were unable to provide a reliable estimation of Pb concentration in the municipal landfill leachate (ML) due to the absence of organic ligands capable of forming stable complexes with the lead. Water provided the closest representation of lead leaching from the non-stabilized and phosphate stabilized soils while sodium tetraborate buffer was found to be suitable for cement-stabilized soil in a non-putrescible landfill leachate system. A comparison of stabilization methods revealed that the buffered phosphate technique was more suitable for stabilizing the lead in the soil relative to cement stabilization.

Evaluating the applicability of a modified toxicity characteristic leaching procedure (TCLP) for the classification of cementitious wastes containing lead and cadmium.

Having the toxicity characteristic leaching procedure (TCLP) as a starting point, this study examined the effect of the various leaching parameters on the leaching of Pb and Cd from cementitious wastes. Using modified TCLP procedures, the parameters investigated were the acid concentration, leaching duration, particle size of the crushed waste, liquid to solid ratio, and the acid type. The main finding was that the final leachate pH controls the leachability of metals due to its influence on their solubility. The high alkalinity of cementitious waste buffers the leachate at a pH where most metals become insoluble. The TCLP was found to result in an unrealistic condition for cementitious wastes due to the high resultant leachate pH.

Stimuli-responsive functionalized mesoporous silica nanoparticles for drug release in response to various biological stimuli.

A silica-based mesoporous nanosphere (MSN) controlled-release drug delivery system has been synthesized and characterized. The system uses l-cysteine derivatized gold nanoparticles (AuNPs), bound to the MSNs using Cu2+ as a bridging ion. The AuNPs serve as removable caps that hinder the release of drug molecules inside the amino functionalized MSN mesoporous framework. The modified MSNs themselves exhibit negligible cytotoxicity to living cells, as revealed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The drug delivery system requires one of two biological stimuli to trigger drug release. These stimuli are either: low pH (pH < 5); or elevated levels of adenosine triphosphate (ATP) (concentration > 4 mM). The feasibility of biologically controlled release was demonstrated through the stimuli-induced removal of the AuNP caps over the MSN releasing the anticancer drug doxorubicin. We envisage that this MSN system could play a significant role in developing new generations of controlled-release delivery vehicles.