Multiplexable and Scalable Aqueous Synthesis Platform for Oleate-Based, Bilayer-Coated Gold Nanoparticles.

Despite gold-based nanomaterials having a unique role in nanomedicine, among other fields, synthesis limitations relating to reaction scale-up and control result in prohibitively high gold nanoparticle costs. In this work, a new preparation procedure for lipid bilayer-coated gold nanoparticles in water is presented, using sodium oleate as reductant and capping agent. The seed-free synthesis not only allows for size precision (8-30 nm) but also remarkable particle concentration (10 mm Au). These reaction efficiencies allow for multiplexing and reaction standardization in 96-well plates using conventional thermocyclers, in addition to simple particle purification via microcentrifugation. Such a multiplexing approach also enables detailed spectroscopic investigation of the nonlinear growth process and dynamic sodium oleate/oleic acid self-assembly. In addition to scalability (at gram-level), resulting gold nanoparticles are stable at physiological pH, in common cell culture media, and are autoclavable. To demonstrate the versatility and applicability of the reported method, a robust ligand exchange with thiolated polyethylene glycol analogues is also presented.

Reductive Dissolution of NCM Cathode through Anaerobic Respiration by Shewanella putrefaciens.

The consumption of lithium-ion batteries (LIBs) has considerably increased over the past decade, leading to a rapid increase in the number of spent LIBs. Exposing spent LIBs to the environment can cause serious environmental harm; however, there is a lack of experimentally obtained information regarding the environmental impacts of abandoned cathode materials. Here, we report the interactions between Shewanella putrefaciens, a microorganism commonly found in diverse low-oxygen natural settings, and LiNi0.6Co0.2Mn0.2O2 (NCM622) under anaerobic conditions. We present compelling evidence that the anaerobic respiration of Shewanella putrefaciens triggers ∼59 and ∼78% dissolution of 0.2 g/L pristine and spent NCM622, respectively. We observed that Shewanella putrefaciens interacted with the pristine and the spent NCM622 under anaerobic conditions at a neutral pH and room temperature and induced the reduction of Ni, Co, and Mn, resulting in the subsequent dissolution of Li, Ni, Co, and Mn. Moreover, we found that secondary mineralization occurred on the surface of reacted NCM622. These findings not only shed light on the substantial impact of microbial respiration on the fate of discarded cathode materials in anaerobic environments but also reveal the potential for sustainable bioleaching of cathodes in spent LIBs.

Microbial Reductive Dechlorination by a Commercially Available Dechlorinating Consortium Is Not Inhibited by Perfluoroalkyl Acids (PFAAs) at Field-Relevant Concentrations.

Perfluoroalkyl acids (PFAAs) have been shown to inhibit biodegradation (i.e., organohalide respiration) of chlorinated ethenes. The potential negative impacts of PFAAs on microbial species performing organohalide respiration, particularly Dehalococcoides mccartyi (Dhc), and the efficacy of in situ bioremediation are a critical concern for comingled PFAA-chlorinated ethene plumes. Batch reactor (no soil) and microcosm (with soil) experiments, containing a PFAA mixture and bioaugmented with KB-1, were completed to assess the impact of PFAAs on chlorinated ethene organohalide respiration. In batch reactors, PFAAs delayed complete biodegradation of cis-1,2-dichloroethene (cis-DCE) to ethene. Maximum substrate utilization rates (a metric for quantifying biodegradation rates) were fit to batch reactor experiments using a numerical model that accounted for chlorinated ethene losses to septa. Fitted values for cis-DCE and vinyl chloride biodegradation were significantly lower (p < 0.05) in batch reactors containing ≥50 mg/L PFAAs. Examination of reductive dehalogenase genes implicated in ethene formation revealed a PFAA-associated change in the Dhc community from cells harboring the vcrA gene to those harboring the bvcA gene. Organohalide respiration of chlorinated ethenes was not impaired in microcosm experiments with PFAA concentrations of 38.7 mg/L and less, suggesting that a microbial community containing multiple strains of Dhc is unlikely to be inhibited by PFAAs at lower, environmentally relevant concentrations.

Pharmacological Comparison of Mitragynine and 7-Hydroxymitragynine: In Vitro Affinity and Efficacy for µ-Opioid Receptor and Opioid-Like Behavioral Effects in Rats.

Relationships between µ-opioid receptor (MOR) efficacy and effects of mitragynine and 7-hydroxymitragynine are not fully established. We assessed in vitro binding affinity and efficacy and discriminative stimulus effects together with antinociception in rats. The binding affinities of mitragynine and 7-hydroxymitragynine at MOR (Ki values 77.9 and 709 nM, respectively) were higher than their binding affinities at κ-opioid receptor (KOR) or δ-opioid receptor (DOR). [35S]guanosine 5'-O-[γ-thio]triphosphate stimulation at MOR demonstrated that mitragynine was an antagonist, whereas 7-hydroxymitragynine was a partial agonist (Emax = 41.3%). In separate groups of rats discriminating either morphine (3.2 mg/kg) or mitragynine (32 mg/kg), mitragynine produced a maximum of 72.3% morphine-lever responding, and morphine produced a maximum of 65.4% mitragynine-lever responding. Other MOR agonists produced high percentages of drug-lever responding in the morphine and mitragynine discrimination assays: 7-hydroxymitragynine (99.7% and 98.1%, respectively), fentanyl (99.7% and 80.1%, respectively), buprenorphine (99.8% and 79.4%, respectively), and nalbuphine (99.4% and 98.3%, respectively). In the morphine and mitragynine discrimination assays, the KOR agonist U69,593 produced maximums of 72.3% and 22.3%, respectively, and the DOR agonist SNC 80 produced maximums of 34.3% and 23.0%, respectively. 7-Hydroxymitragynine produced antinociception; mitragynine did not. Naltrexone antagonized all of the effects of morphine and 7-hydroxymitragynine; naltrexone antagonized the discriminative stimulus effects of mitragynine but not its rate-decreasing effects. Mitragynine increased the potency of the morphine discrimination yet decreased morphine antinociception. Here we illustrate striking differences in MOR efficacy, with mitragynine having less than 7-hydroxymitragynine. SIGNIFICANCE STATEMENT: At human µ-opioid receptor (MOR) in vitro, mitragynine has low affinity and is an antagonist, whereas 7-hydroxymitragynine has 9-fold higher affinity than mitragynine and is an MOR partial agonist. In rats, intraperitoneal mitragynine exhibits a complex pharmacology including MOR agonism; 7-hydroxymitragynine has higher MOR potency and efficacy than mitragynine. These results are consistent with 7-hydroxymitragynine being a highly selective MOR agonist and with mitragynine having a complex pharmacology that combines low efficacy MOR agonism with activity at nonopioid receptors.

Surface-Engineered Nanomaterials in Water: Understanding Critical Dynamics of Soft Organic Coatings and Relative Aggregation Density.

Inorganic-organic nanocomposites, typically as an inorganic core with surface organic coating(s), have received interest as potential platform materials for sensor, catalyst, sorbent, and environmental applications, among others. Here, we describe the critical role of organic surface coatings with regard to the colloidal stability of engineered manganese oxide nanoparticles (MnxOy NPs). Specifically, we prepared libraries of monodisperse MnxOy NPs with a serial selection of surface coatings (stearic acid (SA), oleic acid (OA), poly(maleic anhydride-alt-1-octadecene) (PMAO), linear polyethyleneimine (LPEI), and multibranched polyethyleneimine (BPEI)), which were chosen based on comparable structure(s) and functional group(s). We systematically evaluated the role of surface organic coatings via critical coagulation concentrations (CCCs), which were compared with theoretical calculations (Schulze-Hardy rule). Through a newly developed light scattering protocol, we observed that the effective density of nanoclusters can exceed NPs' primary (bulk) density depending on the open space(s) within organic coatings. Interestingly, PMAO-coated NPs were more stable at the point of zero charge (PZC) than at neutral pH (pH 7), despite the loss of effective surface charge potential. CCC was 334 mM in NaCl and 1.5 mM in CaCl2 at pH 7, compared to CCC values of 807 mM in NaCl and 210 mM in CaCl2 at PZC. This increase in stability is due to polymer (re)configuration (at PZC), which was further confirmed with a quartz crystal microbalance-based technique to evaluate surface-based polymer dynamics. Taken together, this work quantifies the role of organic coating dynamics, including structure, grafting density, and configuration on the colloidal stability of organic-coated NPs.

Delineating the Relationship between Nanoparticle Attachment Efficiency and Fluid Flow Velocity.

The ability to fundamentally describe nanoparticle (NP) transport in the subsurface underpins environmental risk assessment and successful material applications, including advanced remediation and sensing technologies. Despite considerable progress, our understanding of NP deposition behavior remains incomplete as there are conflicting reports regarding the effect of fluid flow velocity on attachment efficiency. To directly address this and more accurately describe NP attachment behavior, we have developed a novel protocol using a quartz crystal microbalance with dissipation monitoring (QCM-D) to separate and individually observe deposition mechanisms (diffusion and sedimentation), providing in situ, real-time information about particle diffusion (from the bulk liquid to solid surface). Through this technique, we have verified that the approaching velocity of NPs via diffusion increases (0.8-6.7 µm/s) with increasing flow velocity (6.1-106.0 µm/s), leading to an increased NP kinetic energy, thus affecting deposition processes. Further, in the presence of a secondary energy minimum associated with organic surface coatings, secondary minimum deposition decreases and primary minimum deposition increases with the flow velocity. NPs deposited at the primary minimum are relatively more resistant to hydrodynamic energies (including detachment associated energies), resulting in an increase of observed attachment efficiencies. Taken together, this work not only describes a novel method to delineate and quantify physical processes underpinning particle behavior but also provides direct measurements regarding key factors defining the relationship(s) of flow velocity and particle attachment. Such insight is valuable for next-generation fate and transport model accuracy, especially under unfavorable attachment regimes, which is a current and critical need for subsurface material applications and implication paradigms.

Formation and Transport of Cr(III)-NOM-Fe Colloids upon Reaction of Cr(VI) with NOM-Fe(II) Colloids at Anoxic-Oxic Interfaces.

Natural organic matter-iron (NOM-Fe) colloids are ubiquitous at anoxic-oxic interfaces of subsurface environments. Fe(II) or NOM can chemically reduce Cr(VI) to Cr(III), and the formation of Cr(III)-NOM-Fe colloids can control the fate and transport of Cr. We explored the formation and transport of Cr(III)-humic acid (HA)-Fe colloids upon reaction of Cr(VI) with HA-Fe(II) colloids over a range of environmentally relevant conditions. Cr(VI) was completely reduced by HA-Fe(II) complexes under anoxic conditions, and the formation of Cr(III)-HA-Fe colloids depended on HA concentration (or molar C/Fe ratio) and redox conditions. No colloids formed at HA concentrations below 3.5 mg C/L (C/Fe ratio below 1.6), but Cr(III)-HA-Fe colloids formed at higher HA concentrations. In column experiments, Cr(III)-HA-Fe(III) colloids formed under oxic conditions were readily transported through sand-packed porous media. Colloidal stability measurements further suggest that Cr(III)-HA-Fe colloids are highly stable and persist for at least 20 days without substantial change in particle size. This stability is attributed to the enrichment of free HA adsorbed on the Cr(III)-HA-Fe colloid surfaces, intensifying the electrostatic and/or steric repulsion interactions between particles. The new insights provided here are important for evaluating the long-term fate and transport of Cr in organic-rich redox transition zones.

Cr(VI) Adsorption on Engineered Iron Oxide Nanoparticles: Exploring Complexation Processes and Water Chemistry.

Surface-functionalized magnetic nanoparticles are promising adsorbents due to their large surface areas and ease of separation after contaminant removal. In this work, the affinity of Cr(VI) adsorption to 8 nm surface-functionalized superparamagnetic magnetite nanoparticles was determined for surface coatings with amine (trimethyloctadecylammonium bromide, CTAB) and carboxyl (stearic acid, SA) functional groups. Cr(VI) adsorbed more strongly to the CTAB-coated nanoparticles than to the SA-coated materials due to electrostatic interactions between positively charged CTAB and anionic Cr(VI) species. The adsorption of Cr(VI) by CTAB- and SA-coated nanoparticles increased with decreasing pH (4.5-10), which could be simulated by a surface complexation model. Cr(VI) removal performance by the nanocomposite was evaluated for two realistic drinking water compositions. The co-occurrence of divalent cations (Ca2+ and Mg2+) and Cr(VI) resulted in decreased Cr(VI) adsorption as particles were destabilized, leading to the aggregation and lower effective surface area, confirming the importance of the overall water composition on the performance of novel engineered nanomaterials for water treatment applications.

Elucidating the Role of Sulfide on the Stability of Ferrihydrite Colloids under Anoxic Conditions.

While the reaction mechanisms between ferrihydrite and sulfide are well-documented, the role of redox reactions on the particle-particle stability of ferrihydrite colloids is largely overlooked. Such reactions are critical for a number of (bio)geochemical processes governing ferrihydrite-based colloid processing and their associated role in nutrient and contaminant subsurface dynamics. Taking a fundamental colloid chemistry approach, along with a complementary suite of characterization techniques, here, we explore the stability mechanisms of ferrihydrite colloids over a wide range of environmentally relevant sulfide concentrations at pH 6.0. Results show that sulfide lowered the stability of both ferrihydrite colloids in a concentration-dependent fashion. At lower sulfide concentrations (15.6-62.5 µM), ferrihydrite colloids are apparently stable, but their critical coagulation concentration (CCC) in NaCl linearly decreases with increasing sulfide concentration. This is attributed to the formation of negatively charged elemental sulfur (S(0)) nanoparticles on the surfaces of positively charged ferrihydrite, intensifying the electrostatic attractions between oppositely charged regions on adjacent ferrihydrite surfaces. Further increasing sulfide concentration generates more S(0) attaching to the ferrihydrite surface. This results in effective surface charge neutralization and then subsequent charge reversal, leading to extensive aggregation of ferrihydrite (core) colloids. Interestingly, for the ferrihydrite colloids with higher hydrodynamic diameter, aggregation rates linearly decreases with increasing sulfide concentration from 156.3 to 312.5 µM, which is likely due to the formation of substantial amounts of negatively charged S(0) and FeS. Findings highlight the significance of sulfidation products in controlling the stability of ferrihydrite colloids in sulfidic environments.

Measurement and Surface Complexation Modeling of U(VI) Adsorption to Engineered Iron Oxide Nanoparticles.

Surface-functionalized magnetite nanoparticles have high capacity for U(VI) adsorption and can be easily separated from the aqueous phase by applying a magnetic field. A surface-engineered bilayer structure enables the stabilization of nanoparticles in aqueous solution. Functional groups in stearic acid (SA), oleic acid (OA), and octadecylphosphonic acid (ODP) coatings led to different adsorption extents (SA≈ OA > ODP) under the same conditions. The impact of water chemistry (initial loading of U(VI), pH, and the presence of carbonate) has been systematically examined for U(VI) adsorption to OA-coated nanoparticles. A diffuse double layer surface complexation model was developed for surface-functionalized magnetite nanoparticles that could simulate both the measured surface charge and the U(VI) adsorption behavior at the same time. With a small set of adsorption reactions for uranyl hydroxide and uranyl carbonate complexes to surface sites, the model can successfully simulate the entire adsorption data set over all uranium loadings, pH values, and dissolved inorganic carbon concentrations. The results show that the adsorption behavior was related to the changing U(VI) species and properties of surface coatings on nanoparticles. The model could also fit pH-dependent surface potential values that are consistent with measured zeta potentials.