Surface Functional Groups Affect Iron (Hydr)oxide Heterogeneous Nucleation: Implications for Membrane Scaling.

Because of its favorable thermodynamics and fast kinetics, heterogeneous solid nucleation on membranes triggers early-stage mineral scaling. Iron (hydr)oxide, a typical membrane scale, initially forms as nanoparticles that interact with surface functional groups on membranes, but these nanoscale phenomena are difficult to observe in real time. In this study, we utilized in situ grazing incidence small angle X-ray scattering and ex situ atomic force microscopy to examine the heterogeneous nucleation of iron (hydr)oxide on surface functional groups commonly used in membranes, including hydroxyl (OH), carboxyl (COOH), and fluoro (F) groups. We found that, compared to nucleation on hydrophilic OH- and COOH-surfaces, the high hydrophobicity of an F-modified surface significantly reduced the extents of both heterogeneously and homogeneously formed iron (hydr)oxide nucleation. Moreover, on the OH-surface, the high functional group density of 0.76 nmol/cm2 caused faster heterogeneous nucleation than that on a COOH-surface, with a density of 0.28 ± 0.04 nmol/cm2. The F-surface also had the highest heterogeneous nucleation energy barrier (26 ± 0.6 kJ/mol), followed by COOH- (23 ± 0.8 kJ/mol) and OH- (20 ± 0.9 kJ/mol) surfaces. The kinetic and thermodynamic information provided here will help us better predict the rates and extents of early-stage scaling of iron (hydr)oxide nanoparticles in membrane processes.

Oxidative Roles of Polystyrene-Based Nanoplastics in Inducing Manganese Oxide Formation under Light Illumination.

Every year, large quantities of plastics are produced and used for diverse applications, growing concerns about the waste management of plastics and their release into the environment. Plastic debris can break down into millions of pieces that adversely affect natural organisms. In particular, the photolysis of micro/nanoplastics can generate reactive oxygen species (ROS). However, their oxidative roles in initiating redox chemical reactions with heavy and transition metals have received little attention. In this study, we investigated whether the photolysis of polystyrene (PS) nanoplastics can induce the oxidation of Mn2+(aq) to Mn oxide solids. We found that PS nanoplastics not only produced peroxyl radicals (ROO•) and superoxide radicals (O2•-) by photolysis, which both play a role in unexpected Mn oxidation, but also served as a substrate for facilitating the heterogeneous nucleation and growth of Mn oxide solids and controlling the formation rate and crystalline phases of Mn oxide solids. These findings help us to elucidate the oxidative roles of nanoplastics in the oxidation of redox-active metal ions. The production of ROS from nanoplastics in the presence of light can endanger marine life and human health, and affect the mobility of the nanoplastics in the environment via redox reactions, which in turn may negatively impact their environmental remediation.

Effects of MoS2 Layer Thickness on Its Photochemically Driven Oxidative Dissolution.

The distinctive optical and electronic properties of two-dimensional (2D) molybdenum disulfide (MoS2) make it a promising photocatalyst and photothermal agent in aqueous applications. In terms of environmental stability, MoS2 has been considered insoluble, but 2D MoS2 nanosheets can be susceptible to dissolution, owing to their large surface areas and highly accessible reactive sites, including defects at the basal plane and edge sites. Under light illumination, the dissolution of 2D MoS2 nanosheets can be further accelerated by their photochemical reactivity. To elucidate MoS2 reactivity in the environment, here we investigated the thickness-dependent dissolution of MoS2 under illumination. To synthesize nanoscale thicknesses of MoS2, we exfoliated bulk MoS2 by ultrasonication and controlled the layer thickness by iterative cascade centrifugation, producing MoS2 nanosheets averaging either ∼18 nm or ∼46 nm thick, depending on the centrifugation rate. Under simulated sunlight, MoS2 dissolution was accelerated, the Mo6+ composition increased, and the solution pH decreased compared to those in the dark. These results suggest that light exposure promotes the oxidation of MoS2, causing faster dissolution. Importantly, 18 nm thick MoS2 exhibited faster dissolution than either 46 nm or bulk MoS2, driven by the superoxide radical (O2•-) generation promoted by its relative thinness. These findings highlight the important role of the thickness-dependent photochemistry of MoS2 nanosheets in their dissolution, which is directly linked to their environmental behavior and stability.

Dissolution of PbS, CuS, and ZnS in oxic waters: effects of adsorbed natural organic matter.

Metal sulfides serve as sinks of toxic heavy metals in anoxic sediments. Suspension of metal sulfides to oxic water columns may cause their oxidative dissolution, leading to the release of toxic heavy metal ions. Ubiquitous natural organic matter (NOM) could adsorb on the surfaces of metal sulfides and influence their dissolution. In this study, the dissolution of suspended PbS, CuS, and ZnS with different levels of adsorbed NOM was investigated. The rates of metal release showed the following order after normalization by the available surface areas: PbS > CuS > ZnS. The adsorbed NOM was found to inhibit the oxidative dissolution of PbS and ZnS; the degree of inhibition was enhanced by increased levels of NOM adsorption. In contrast, the dissolution of CuS was found to increase and then decrease with increased levels of NOM adsorption. These results show that adsorbed NOM can promote metal release via ligand-induced dissolution, as well as inhibit metal release by forming a barrier against oxygen and proton attacks. The relative importance of these processes is metal specific and governs the overall impacts of NOM adsorption on the dissolution of metal sulfides. The results imply that remobilization of heavy metals from contaminated sediments during intensified storm events should be carefully evaluated in terms of metals of concern and levels of organic matter adsorption.

Effects of dissolved oxygen, pH, salinity and humic acid on the release of metal ions from PbS, CuS and ZnS during a simulated storm event.

Metal sulfides serve as the sinks of toxic heavy metals in anoxic sediments. Once exposed to fluctuations in environmental conditions, dissolution of metal sulfides can occur and release toxic heavy metal ions into water column. In this study, we investigated the effects of dissolved oxygen (DO), pH, salinity and humic acid (HA) on the dissolution of CuS, PbS and ZnS using batch experiments with continuous aeration to simulate the re-suspension of these metal sulfides during a storm event. Experimental results indicated that oxidative dissolution of CuS, PbS and ZnS occurred in the presence of DO. The rate was the fastest for PbS, followed by CuS and ZnS. Soluble metal concentrations also increased with decreasing pH under oxic conditions. Compared to metal sulfides dissolution rates in freshwater without HA, the presence of saline conditions and HA generally accelerated the dissolution of CuS but inhibited the dissolution of PbS and ZnS. A higher saline or HA concentration, however, did not always lead to a stronger enhanced or inhibited dissolution rate, which could be a collective effect resulting from ligand-enhanced dissolution, complexation, and decreased oxygen and proton attacks due to HA adsorption on the metal sulfide surfaces.

Glucosamine sulfate inhibits TNF-alpha and IFN-gamma-induced production of ICAM-1 in human retinal pigment epithelial cells in vitro.

PURPOSE: Glucosamine sulfate (GS) is a naturally occurring sugar that possesses some immunosuppressive effects in vitro and in vivo, but its mechanism is unknown. We investigated whether GS could modulate the proinflammatory cytokine-induced expression of the gene for intercellular adhesion molecule (ICAM)-1, an inflammatory protein in human retinal pigment epithelial (RPE) cells. METHODS: ARPE-19 cells were used as a model to determine the effects of GS on the expression of the ICAM-1 gene upregulated by TNF-alpha or IFN-gamma, by Western blot analysis and semiquantitative reverse transcription polymerase chain reaction (RT-PCR). The activation and nuclear translocation of the nuclear factors NF-kappaB and STAT1 were evaluated by immunocytochemistry, Western blot analysis, and electrophoretic mobility shift assay (EMSA). RESULTS: Both TNF-alpha and IFN-gamma increased the expression of ICAM-1 at the mRNA and protein levels in a time- and dose-dependent manner in ARPE-19 cells. GS effectively downregulated the TNF-alpha- or IFN-gamma-induced expression of ICAM-1 in the protein and mRNA level in a dose-dependent manner. GS further inhibited the nuclear translocation of p65 proteins in TNF-alpha and phosphorylated STAT1 in IFN-gamma-stimulated ARPE-19 cells. CONCLUSIONS: GS inhibits the expression of the ICAM-1 gene in ARPE-19 cell stimulated with TNF-alpha or IFN-gamma through blockade of NF-kappaB subunit p65 and nuclear translocation of STAT1. This study has demonstrated a potentially important property of GS in reducing ICAM-1 mediated inflammatory mechanisms in the eye.

Contrast sensitivity after +Gz acceleration.

BACKGROUND: This study was designed to determine the extent and duration of contrast sensitivity (CS) loss after high sustained +Gz acceleration in a centrifuge. METHODS: The subjects were 12 healthy male flight surgeons between 20 and 22 (mean = 21.1) yr of age. The human centrifuge at the Aviation Physiology Research Laboratory in Tainan, Taiwan, was used to expose the subjects to an acceleration profile. Each subject experienced three centrifuge runs made up of one gradual onset and two rapid onset profiles. Contrast sensitivity (CS) was measured before, and at 5 min, 10 min, and 20 min for the right eye; and 7 min, 12 min, and 22 min for the left eye after the acceleration. Both eyes were measured with the right eye being tested first. RESULTS: There was a generalized depression of CS at 5-12 min for both eyes. The depression was more severe at low and medium frequencies (1.5, 3.0, 6.0 cycles per degree, cpd) than at a high spatial frequency (18.0 cpd). There was a significant decrease in CS of the right eye at 1.5 cpd (p < 0.05 between control and 5 min), and on the left eye at 3.0 cpd (p < 0.05 between control and 7 min, p < 0.05 between control and 12 min) and 6.0 cpd (p < 0.05 between control and 12 min). The CS loss was more obvious at 5-12 min for both eyes, and there was only partial recovery at 22 min after the acceleration. CONCLUSIONS: These results demonstrated that +Gz acceleration is associated with CS loss. The recovery time was greater than expected. Factors other than ocular blood flow may be involved in the prolonged CS loss.

Corneal iron ring associated with orthokeratology.

Two teenaged girls had orthokeratology to correct myopia. The postoperative development of corneal iron rings in both eyes was disclosed by a biomicroscopic examination at 3 months in 1 patient and 5 months in the other. The location of the corneal iron rings coincided with the fitting curve of the reverse-geometry rigid contact lens, suggesting that the rings might have developed from tear pooling.

Effect of sympathetic denervation on rabbit choroidal blood flow.

In this study we demonstrate the existence of sympathetic innervation and compare the effect of unilateral or bilateral superior cervical sympathectomy on albino rabbit choroidal blood flow (CBF) during changes in perfusion pressure (PP). Forty albino rabbits weighing between 2.0 and 3.0 kg were randomly divided into three groups. The bilateral sympathectomy group (group S) included 10 rabbits (20 eyes) that received bilateral sympathectomy 1 week prior to the study. The unilateral sympathectomy group (group U) included 20 rabbits (20 eyes) that received unilateral sympathectomy 1 week prior to the study. Only the eyes ipsilateral to sympathectomy were utilized. The other 10 rabbits (20 eyes) served as controls (group N), each received the same procedure as the experimental groups except that the superior cervical ganglion (SCG) was preserved. The blood cell flux (PF), velocity (V), and concentration of moving blood cells (CMBC) were recorded simultaneously by means of a laser Doppler flowmeter (Perimed PF4001), while the intraocular pressure was increased linearly with a syringe pump. When the PP decreased steadily, the PF, V, and CMBC remained constant until PP <55 mm Hg, then decreased proportionally to the PP. When the PP decreased from 75 to 0 mm Hg, the PF, V and CMBC decreased from 100 to 6.87 +/- 0.97%, 8.44 +/- 0.92%, and 18.67 +/- 0.91% in group N, to 18.56 +/- 1.62%, 19.30 +/- 1.84%, and 38.02 +/- 9.10% in group U, and to 18.38 +/- 2.89%, 16.78 +/- 1.48%, and 34.58 +/- 4.42% in group S. The changes in PF, V, and CMBC were similar in groups S and U. Both group S and U had higher PF, V, and CMBC values than group N at comparable PPs below 55 mm Hg. These results indicate that the SCG plays a role in CBF regulation. Both unilateral and bilateral sympathectomy led to a higher PF in both groups S and U rabbits, indicating increased CBF while PP decreased gradually. This suggests that the rabbit choroid does not receive crossed innervation. The plateau response in each curve demonstrates the presence of autoregulation. This autoregulation was unchanged by either unilateral or bilateral sympathetic denervation.

Inducible adeno-associated virus vector-delivered transgene expression in corneal endothelium.

PURPOSE: To investigate whether recombinant adeno-associated virus (rAAV) vector--mediated transgene expression is induced by inflammation in corneal endothelial cells in vivo. METHODS: The ocular anterior chamber of New Zealand White rabbits was injected with rAAV-LacZ (10(7) units of infection). Transient ocular anterior segment inflammation was induced by an intravitreal injection of lipopolysaccharide (LPS). The effect of inflammation on LacZ gene expression in corneal endothelial cells was evaluated by histochemical staining and reverse transcription-polymerase chain reaction (RT-PCR). The influence of rAAV on endothelial cell function was monitored by measuring corneal thickness. RESULTS: Inflammatory reaction peaked at 1 day after LPS treatment and, at the same time, most of the endothelial cells (91.3% plus minus 7.2%) showed prominent LacZ gene expression. The transgene expression gradually diminished to basal level (3.4% plus minus 2.1%) when the inflammation subsided at 15 days after LPS treatment. The diminished transgene expression was efficiently reactivated to a high level (86.1% plus minus 8.7%) by a second LPS injection 60 days later. Moreover, the transgene expression remained low for a long period (60 days) in the absence of LPS treatment, but was increased to high levels (87.3% plus minus 8.1%) 1 day after LPS treatment. Throughout the observation period, endothelial cell function remained intact. CONCLUSIONS: The rAAV vector can deliver genes into endothelial cells, and transgene expression is dramatically induced by inflammation. The rAAV-delivered transgene is stable and does not compromise endothelial cell function. Inducible rAAV-mediated transgene expression in corneal endothelial cells is a potential strategy in the treatment and prevention of ocular diseases.