Chemical Aspects of Halide Perovskite Nanocrystals

Halide perovskite nanocrystals (HPNCs) are currently among the most intensely investigated group of materials. Structurally related to the bulk halide perovskites (HPs), HPNCs are nanostructures with distinct chemical, optical, and electronic properties and significant practical potential. One of the keys to the effective exploitation of the HPNCs in advanced technologies is the development of controllable, reproducible, and scalable methods for preparation of materials with desired compositions, phases, and shapes and low defect content. Another important condition is a quantitative understanding of factors affecting the chemical stability and the optical and electronic properties of HPNCs. Here we review important recent developments in these areas. Following a brief historical prospective, we provide an overview of known chemical methods for preparation of HPNCs and approaches used to control their composition, phase, size, and shape. We then review studies of the relationship between the chemical composition and optical properties of HPNCs, degradation mechanisms, and effects of charge injection. Finally, we provide a short summary and an outlook. The aim of this review is not to provide a comprehensive summary of all relevant literature but rather a selection of highlights, which, in the subjective view of the authors, provide the most significant recent observations and relevant analyses.

A simple and fast alternative method to remove glycerol from chicken semen after cryopreservation

A concentration of 11% of glycerol is the standard one for sperm cryopreservation in chickens, however, the presence of just 2% glycerol already causes severe fertility reduction, suggesting the necessity of removing glycerol before artificial insemination (AI). The major approach developed for this purpose is serial dilution followed by centrifugation (SDC), which demands special equipment (such as a refrigerate room) to maintain post-thaw semen at 4 °C, besides being time consuming. Therefore, we attempted to develop a simple method to remove glycerol from chicken frozen-thawed semen based on a colloidal gel, Percoll, which is ordinarily used to select motile and viable sperm in mammals as well as in fresh chicken semen. In this study, we used a Percoll based glycerol removal solution (GRS) containing sucrose to avoid frozen-thawed sperm suffering from osmotic stress. Subsequently, several conditions including GRS compositions (GRS A, B, C and D) and centrifugation temperatures (4 and 20 °C) were compared by their influence on sperm in vitro parameters. Afterwards, GRS A and D were selected for fertility evaluation, compared to conventional SDC method. Our results showed that the fertility with GRS A at both 4 and 20 °C were higher than GRS D (p < 0.05) and similar or even superior to the fertility obtained with SDC method. Altogether, our novel GRS protocol is a valuable method for chicken sperm cryobanking policy, supported by its notable results of fertility as well as saving 44% of time, with a simple equipment at flexible operation temperatures of 4 or 20 °C.

A Real-Time In Situ Demonstration of Direct and Indirect Transformation Pathways in CdTe Magic-Size Clusters at Room Temperature

The transformations of colloidal semiconductor magic-size clusters (MSCs) are expected to occur with only discrete, step-wise redshifts in optical absorption. Here, we challenge this assumption presenting a novel, conceptually different transformation, for which the redshift is continuous. In the room-temperature transformation from CdTe MSC-448 to MSC-488 (designated by the peak wavelengths in nanometer), the redshift of absorption monitored in situ displays distinctly continuous and/or step-wise behavior. Based on conclusive evidence provided by real-time experiments, the former transformation is apparently direct and intra-cluster with a relatively large energy barrier. The latter transformation is indirect and assisted by MSC precursor compounds (PCs). The former transformation follows the latter often, being predominant at a relatively high temperature. The present findings encourage a reconsideration of the absorption redshift reported previously for transformations of binary II-VI MSCs, together with the pathway associated without the increase of cluster mass.

Dynamics of trace metals with different size species in the Pearl River Estuary, Southern China

The Pearl River Estuary (PRE), the largest estuary in Southern China, regulates the fluxes of riverine trace metals into the South China Sea. However, the geochemical behavior of trace metals in this estuary is still ambiguous. In this study, we investigated the dynamics of trace metals in different phases (i.e., particulate, colloidal and truly dissolved) in the PRE in both wet and dry seasons characteristic of the region. Transformations of trace metals between particulate (>0.45 μm), colloidal (1 kDa to 0.45 μm) and truly dissolved (<1 kDa) phases were observed during the estuarine mixing. Colloidal metals (except for Pb) showed non-conservative 'removal' behavior in the low-salinity zone (S < 10‰), suggesting the coagulation of colloidal metals and subsequent deposition to bed sediments being an important sink of dissolved trace metals. By contrast, truly dissolved metals exhibited a mid-salinity maximum distribution (i.e., Mn, Ni, Cu and Cd) or little variation along the salinity gradient (i.e., Fe). The increase of truly dissolved metal concentration was accompanied by the decrease of particulate metal concentration, indicating that the desorption of suspended particles was an important source of dissolved Mn and Cd in the PRE. Metal released from the suspended particles increased in the dry season due to the high suspended particulate matter concentration. Dissolved Mn concentration in the bottom water in wet season was higher than that in dry season, implying that benthic Mn input increased as the bottom water became hypoxic. Abnormally high concentrations of particulate and dissolved Pb were observed at the lower PRE, implying the presence of a potential point source pollution. A flux model predicted that total dissolved Fe, Ni, Cu and Zn underwent net removal while dissolved Mn and Cd had net inputs during the estuarine mixing. This study raveled contrasting geochemical behaviors of trace metals with different size phases and the different sources and sinks of dissolved metals in the PRE.

Physiochemical characterization of highly biocompatible, and colloidal LaF3:Yb/Er upconversion nanoparticles

Highly colloidal upconversion nanoparticles (UCNPs) were synthesized at low temperatures by the thermal decomposition process. The structure, morphology, crystallinity, surface chemistry, and optical properties were systematically optimized and studied through various spectroscopic techniques. X-ray diffraction (XRD) patterns have shown the formation of single-phase, highly purified, well-crystalline, hexagonal LaF₃ NPs, while the TEM micrographs show small, irregular sizes, spherically shaped, and aggregated polycrystalline UCNPs with an average crystalline size of about 8-15 nm. The Negative Zeta Potential value exhibits good biocompatibility of the UCNPs, which supports the idea that surface-anchored hydroxyl groups facilitate the stabilization of the NPs in aqueous media, as well as enhance biomolecules' tagging efficiency. The absorption spectrum, Zeta Potential, and hydrodynamic size that were measured in aqueous media illustrate excellent dispersibility, colloidal stability, biocompatibility, and cytotoxicity character of the UCNPs. Zeta potential and MTT assay studies illustrated high biocompatibility, it could be due to the surface-anchored hydroxyl groups. The nanoproduct demonstrates an excellent UC luminescence spectrum (i.e., prominent green emission ⁴S_3/2 → ⁴I/_15/2) upon irradiation by the 980-nm laser diode. TEM micrographs, further, revealed that this optically active material with aqueous sensitivities, porous crystal structure, and excellent UCNPs, could be a favorable candidate for potential photonics-based bio-related applications.

Investigating organic nitrogen production in activated sludge process: Size fraction and biodegradability

The effect of sludge retention time (SRT) on the production of organic nitrogen (ON) fractions (particulate, colloidal and soluble) and the biodegradability of produced soluble ON in an activated sludge process was investigated. Synthetic wastewater with no ON was fed to the four laboratory-scale reactors operated at SRTs of 2, 5, 10 and 20 d, respectively. Effluent ON from each reactor was fractionated into particulate, colloidal, and soluble ON (pON, cON, and sON). The effluent total ON contained 5.7 to 11.9 mg/L pON, 3.6 to 3.8 mg/L cON, and 2.3 to 4.6 mg/L sON. cON fraction can be larger than sON fraction in the secondary effluent. Therefore, besides focusing on sON, water resource recovery facilities aiming to meet stricter effluent TN limits should also identify appropriate technologies to target cON. More than 50% of effluent sON was biodegradable under SRTs of 2, 5, and 10 d but the biodegradability decreased to 31% at 20-d SRT. Large fractions of non-biodegradable sON (69%) at SRT of 20-d could be contributed by extracellular polymeric substances and soluble microbial products, specifically biomass associated products due to endogenous respiration. Thus, sON generated at long SRTs may take longer to decompose in receiving waters.

Molecular-level understanding of gibbsite particle aggregation in water

Using molecular dynamics simulations, we investigate the molecular scale origin of crystal face selectivity when one gibbsite particle attaches to another in water. A comparison of the free energy per unit surface area of particle-particle attachment indicates that particle attachment through edge surfaces, where the edge surfaces are either (1 0 0) or (1 1 0) crystal faces, is more energetically favorable compared to attachment between two basal surfaces (i.e., (0 0 1) crystal faces) or between the basal surface of one particle and the edge surface of another. This result suggests that gibbsite crystals with low basal/edge surface area ratio will preferentially attach through edge surfaces, potentially helping the crystals grow laterally. However, for larger gibbsite particles (high basal/edge surface area ratio) the total free energy, not normalized by surface area, of particle attachment through the basal surfaces is lower (more negative) than attachment through the edge surfaces, indicating that larger gibbsite particles will preferentially aggregate through basal surface attachments. The short-range electrostatic interactions including the interparticle hydrogen bonds from surface -OH groups drive particle attachment, and the dominant contribution to the free energy minimum is enthalpic rather than entropic. However, the enthalpy of basal-edge attachment is significantly offset by the entropy leading to a higher free energy (less negative) compared to that of basal-basal attachment. Study of the free energy for a few imperfect attachments of two particles indicates a higher free energy (i.e., less negative, less stable), compared to a perfect attachment.

Insights into colloidal nanoparticle-protein corona interactions for nanomedicine applications

Colloidal nanoparticles (NPs) have attracted significant attention due to their unique physicochemical properties suitable for diagnosing and treating different human diseases. Nevertheless, the successful implementation of NPs in medicine demands a proper understanding of their interactions with the different proteins found in biological fluids. Once introduced into the body, NPs are covered by a protein corona (PC) that determines the biological behavior of the NPs. The formation of the PC can eventually favor the rapid clearance of the NPs from the body before fulfilling the desired objective or lead to increased cytotoxicity. The PC nature varies as a function of the different repulsive and attractive forces that govern the NP-protein interaction and their colloidal stability. This review focuses on the phenomenon of PC formation on NPs from a physicochemical perspective, aiming to provide a general overview of this critical process. Main issues related to NP toxicity and clearance from the body as a result of protein adsorption are covered, including the most promising strategies to control PC formation and, thereby, ensure the successful application of NPs in nanomedicine.

Oleic Acid Vesicles as a new Approach for Transdermal Delivery of Econazole Nitrate: Development, Characterization, and In-vivo Evaluation in Wistar rats

BACKGROUND

Cutaneous candidiasis is a deep-seated skin fungal infection that is most commonly observed in immunocompromised patients. This fungal infection is conventionally treated with various formulations like gels and creams which are having different side effects and least therapeutic efficacy. Hence, it becomes necessary to develop a novel carrier system for the treatment of this deep-seated skin fungal infection. Econazole nitrate is the most widely used antifungal for the treatment of cutaneous candidiasis, therefore, in present research work we developed and evaluated econazole nitrate loaded oleic acid vesicles for treatment of cutaneous candidiasis through transdermal route.

METHODS

Econazole nitrate loaded oleic acid vesicles were prepared by thin-film hydration and characterized for drug entrapment, vesicle size, zeta potential, polydispersity index (PDI), Fourier Transform-infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), X-ray diffraction (XRD) analysis. Furthermore, the oleic acid vesicular gel was evaluated for ex-vivo skin permeation/retention and in-vitro and in-vivo antifungal activity in Wistar rats.

RESULTS

Econazole nitrate loaded oleic acid vesicles showed high encapsulation of drug (74.76 ± 3.0%), acceptable size (373.4 ± 2.9 nm), and colloidal characteristics (PDI = 0.231 ± 0.078, zeta potential = -13.27 ± 0.80 mV). The oleic acid vesicular gel showed high skin permeation (Transdermal flux = 61.98 ± 2.45 μg/cm2/h), skin retention (35.90 ± 2.06%), in-vitro, and in-vivo antifungal activity compared to marketed cream (EcodermR) of econazole nitrate for a prolonged period of time (4 days).

CONCLUSION

Developed econazole nitrate loaded oleic acid vesicles could be used effectively in the treatment of cutaneous candidiasis with minimization of side effects of econazole nitrate with increased therapeutic efficacy.

Prevention of Hepatic Ischemia-Reperfusion Injury by Carbohydrate-Derived Nanoantioxidants

Hepatic ischemia-reperfusion injury (IRI), which mainly results from excessive reactive oxygen species (ROS) generated by a reperfusion burst of oxygen, has long been a major cause of liver dysfunction and failure after surgical procedures. Here, a monodispersed hydrophilic carbohydrate-derived nanoparticle (C-NP) was synthesized as a nanoantioxidant that could effectively prevent hepatic IRI. The spherical C-NPs had a size of ∼78 ± 11.3 nm covered with polar surface groups. They were well dispersible in water with good colloidal stability, nontoxicity, and good ROS scavenging capability. The C-NPs also exhibited good circulation lifetime, effective delivery to liver, and gradual degradability with an ability to assist the IRI group maintaining a normal and healthy liver status. The pathology mechanism of C-NPs in hepatic IRI was confirmed to be scavenging of excessive ROS by C-NPs. The effective therapeutic treatment of C-NPs in living animals revealed a great potential in clinical prevention for hepatic IRI.

Characterization of engineered nanoparticles in commercially available spray disinfectant products advertised to contain colloidal silver

Given the potential for human exposure to silver nanoparticles from spray disinfectants and dietary supplements, we characterized the silver-containing nanoparticles in 22 commercial products that advertised the use of silver or colloidal silver as the active ingredient. Characterization parameters included: total silver, fractionated silver (particulate and dissolved), primary particle size distribution, hydrodynamic diameter, particle number, and plasmon resonance absorbance. A high degree of variability between claimed and measured values for total silver was observed. Only 7 of the products showed total silver concentrations within 20% of their nominally reported values. In addition, significant variations in the relative percentages of particulate vs. soluble silver were also measured in many of these products reporting to be colloidal. Primary silver particle size distributions by transmission electron microscopy (TEM) showed two populations of particles - smaller particles (<5nm) and larger particles between 20 and 40nm. Hydrodynamic diameter measurements using nanoparticle tracking analysis (NTA) correlated well with TEM analysis for the larger particles. Z-average (Z-Avg) values measured using dynamic light scattering (DLS); however, were typically larger than both NTA or TEM particle diameters. Plasmon resonance absorbance signatures (peak absorbance at around 400nm indicative of metallic silver nanoparticles) were only noted in 4 of the 9 yellow-brown colored suspensions. Although the total silver concentrations were variable among products, ranging from 0.54mg/L to 960mg/L, silver containing nanoparticles were identified in all of the product suspensions by TEM.

The characterization of iron (III) in seawater and related toxicity to early life stages of scleractinian corals

Currently toxicity data for iron (Fe) in seawater are limited; furthermore, these data are of poor quality as a result of the importance of Fe solubility in test solutions being overlooked. The present study characterized the solubility and lability of Fe(III) in seawater and then examined the effects of Fe(III) on the fertilization success and larval survival of the tropical marine scleractinian corals Acropora spathulata and Platygyra daedalea. We present the first assessment of the effects of Fe on the early life stages of scleractinian corals. Concentrations of both soluble and labile forms of Fe were very low, with dissolved Fe concentrations ≤0.195 mg/L in bioassay test solutions and chemical determinations revealing labile Fe concentrations ≤1.21 mg/L. For fertilization experiments, the median effect concentration (EC50) value for total Fe was 25 mg/L for the most sensitive species, P. daedalea, whereas the EC50 values for A. spathulata ranged between 40 and 66 mg/L. The median lethal concentration value for P. daedalea larval survival was 47 mg/L Fe after 72-h exposure. We provide Fe toxicity data for tropical marine keystone species that could be used to help generate more reliable guideline values for Fe in marine waters. Environ Toxicol Chem 2018;37:1104-1114. © 2017 SETAC.

Size partitioning and mixing behavior of trace metals and dissolved organic matter in a South China estuary

The Jiulong River estuary, located in the southeastern China, suffered from metal pollution due to industrial effluent releases. Mixing of effluent and estuarine water may have significantly affected the size distribution of trace metals and their environmental fate. In the present study, colloidal size distribution of organic matter and selected metals were quantified using asymmetric flow field-flow fractionation (AF4) and ICP-MS. We demonstrated a dominance of dissolved metals in the 1-10kDa fraction, and metals such as Cu, Zn, Ni, Co, Pb, Cd and Mn were mostly regulated by terrestrial fulvic acid. The larger inorganic colloids played a limited role, although Fe reduction was likely to affect the size partitioning of colloidal Mn. The holding pond represented a source of trace metals and chromophoric and humic-like dissolved organic matter to the estuary. Scavenging or removal behavior became evident following the intermittent mixing, and the small sized colloidal organic complexes were responsible for binding and stabilizing trace metals. Variations in particle size distributions indicated different sources, fates and geochemical controls of the metals. Our results highlighted the impacts of both natural and anthropogenic processes on the transformation of trace metals among phases in this dynamic estuary system.

Toxicology of silica nanoparticles: an update

Large-scale production and use of amorphous silica nanoparticles (SiNPs) have increased the risk of human exposure to SiNPs, while their health effects remain unclear. In this review, scientific papers from 2010 to 2016 were systematically selected and sorted based on in vitro and in vivo studies: to provide an update on SiNPs toxicity and to address the knowledge gaps indicated in the review of Napierska (Part Fibre Toxicol 7:39, 2010). Toxicity of SiNPs in vitro is size, dose, and cell type dependent. SiNPs synthesized by wet route exhibited noticeably different biological effects compared to thermal route-based SiNPs. Amorphous SiNPs (particularly colloidal and stöber) induced toxicity via mechanisms similar to crystalline silica. In vivo, route of administration and physico-chemical properties of SiNPs influences the toxicokinetics. Adverse effects were mainly observed in acutely exposed animals, while no significant signs of toxicity were noted in chronically dosed animals. The correlation between in vitro and in vivo toxicity remains less well established mainly due to improper-unrealistic-dosing both in vitro and in vivo. In conclusion, notwithstanding the multiple studies published in recent years, unambiguous linking of physico-chemical properties of SiNPs types to toxicity, bioavailability, or human health effects is not yet possible.

Phase partitioning of trace metals in a contaminated estuary influenced by industrial effluent discharge

Severe trace metal pollution due to industrial effluents releases was found in Jiulong River Estuary, Southern China. In this study, water samples were collected during effluent release events to study the dynamic changes of environmental conditions and metal partitioning among dissolved, particulate and colloidal phases controlled by estuarine mixing. Intermittent effluent discharges during low tide caused decreasing pH and dissolved oxygen, and induced numerous suspended particulate materials and dissolved organic carbon to the estuary. Different behaviors of Cu, Zn, Ni, Cr and Pb in the dissolved fraction against the conservative index salinity indicated different sources, e.g., dissolved Ni from the intermittent effluent. Although total metal concentrations increased markedly following effluent discharges, Cu, Zn, Cr, Pb were predominated by the particulate fraction. Enhanced adsorption onto particulates in the mixing process resulted in elevated partitioning coefficient (Kd) values for Cu and Zn, and the particle concentration effect was not obvious under such anthropogenic impacts. Colloidal proportion of these metals (especially Cu and Zn) showed positive correlations with dissolved or colloidal organic carbon, suggesting the metal-organic complexation. However, the calculated colloidal partitioning coefficients were relatively constant, indicating the excess binding capacity. Overall, the intermittent effluent discharge altered the particulate/dissolved and colloidal/soluble phase partitioning process and may further influence the bioavailability and potential toxicity to aquatic organisms.

Auger-Limited Carrier Recombination and Relaxation in CdSe Colloidal Quantum Wells

Using time-resolved photoluminescence spectroscopy, we show that two-exciton Auger recombination dominates carrier recombination and cooling dynamics in CdSe nanoplatelets, or colloidal quantum wells. The electron-hole recombination rate depends only on the number of electron-hole pairs present in each nanoplatelet, and is consistent with a two-exciton recombination process over a wide range of exciton densities. The carrier relaxation rate within the conduction and valence bands also depends only on the number of electron-hole pairs present, apart from an initial rapid decay, and is consistent with the cooling rate being limited by reheating due to Auger recombination processes. These Auger-limited recombination and relaxation dynamics are qualitatively different from the carrier dynamics in either colloidal quantum dots or epitaxial quantum wells.

Oral toxicity of silver ions, silver nanoparticles and colloidal silver--a review

Orally administered silver has been described to be absorbed in a range of 0.4-18% in mammals with a human value of 18%. Based on findings in animals, silver seems to be distributed to all of the organs investigated, with the highest levels being observed in the intestine and stomach. In the skin, silver induces a blue-grey discoloration termed argyria. Excretion occurs via the bile and urine. The following dose-dependent animal toxicity findings have been reported: death, weight loss, hypoactivity, altered neurotransmitter levels, altered liver enzymes, altered blood values, enlarged hearts and immunological effects. Substantial evidence exists suggesting that the effects induced by particulate silver are mediated via silver ions that are released from the particle surface. With the current data regarding toxicity and average human dietary exposure, a Margin of Safety calculation indicates at least a factor of five before a level of concern to the general population is reached.