Formation Of Stable Aggregates Research Articles

Size reduction of biochar to nanoscale decrease polycyclic aromatic hydrocarbons (PAHs) and metals content and bioavailability in nanobiochar

Objective of this research was to investigate ball milling of biochar from various feedstocks (willow, rice husk, oilseed rape, sewage sludge) under different pyrolysis conditions (500 and 750 °C, N2 and CO2 atmosphere) on polycyclic aromatic hydrocarbons (PAHs) and metals content. A significant reduction in both total (Ctotal Σ16) (1.1 to 2.4-fold decrease) and freely available (Cfree Σ16) (1.1 to 2.9-fold decrease) PAHs in nanobiochar (n-BC), particularly in sewage sludge (SSL)-derived n-BC was observed. The changes in biochar surface characteristics induced by ball milling, such as surface area, pore volume, and hydrophilicity, contribute to the decreased PAHs content. Mechanisms involving mechanochemical degradation, free-radical reactions, and defects on the biochar surface may explain the decrease of PAHs. The n-BC showed lower log Kd values for PAHs (reduced by 14 to 41 %) compared to bulk biochar (b-BC), indicating reduced effectiveness in immobilizing PAHs. The ball milling significantly reduced also metal contents by 37 to 55 %, especially in willow pellets and agricultural residue (rice husk and oilseed rape straw) with optimal reduction (by 55 %) observed for WL-derived n-BC produced at 650 °C. Importantly, no metals were detected in the aqueous phase after ball milling, ensuring environmental safety of these materials. Reduction mechanisms of metals during ball milling include stable aggregate formation, enhanced defects in crystalline structures, and irreversible adsorption onto new surfaces. The results demonstrate that the application of an eco-friendly ball milling method allows for the production of materials characterized by reduced contamination levels, which is crucial from an environmental protection viewpoint.

Stable Aggregate Formation and Microbial Diversity Resilience in Soil Formation of Bauxite Residue: Roles of Extracellular Polymeric Substances Secreted by Penicillium oxalicum

Stable Aggregate Formation and Microbial Diversity Resilience in Soil Formation of Bauxite Residue: Roles of Extracellular Polymeric Substances Secreted by <i>Penicillium oxalicum</i>

Extraction of Common Small Microplastics and Nanoplastics Embedded in Environmental Solid Matrices by Tetramethylammonium Hydroxide Digestion and Dichloromethane Dissolution for Py-GC-MS Determination.

Determination of microplastics and nanoplastics (MNPs), especially small MPs and NPs (<150 μm), in solid environmental matrices is a challenging task due to the formation of stable aggregates between MNPs and natural colloids. Herein, a novel method for extracting small MPs and NPs embedded in soils/sediments/sludges has been developed by combining tetramethylammonium hydroxide (TMAH) digestion with dichloromethane (DCM) dissolution. The solid samples were digested with TMAH, and the collected precipitate was washed with anhydrous ethanol to eliminate the natural organic matter. Then, the MNPs in precipitate were extracted by dissolving in DCM under ultrasonic conditions. Under the optimized digestion and extraction conditions, the factors including sizes and concentrations of MNPs showed insignificant effects on the extraction process. The feasibility of this sample preparation method was verified by the satisfactory spiked recoveries (79.6-91.4%) of polystyrene, polyethylene, polypropylene, poly(methyl methacrylate), polyvinyl chloride, and polyethylene terephthalate MNPs in soil/sediment/sludge samples. The proposed sample preparation method was coupled with pyrolysis gas chromatography-mass spectrometry to determine trace small MPs and NPs with a relatively low detection limit of 2.3-29.2 μg/g. Notably, commonly used MNPs were successfully detected at levels of 4.6-51.4 μg/g in 6 soil/sediment/sludge samples. This proposed method is promising for evaluating small solid-embedded MNP pollution.

Biological soil crusts decrease infiltration but increase erosion resistance in a human-disturbed tropical dry forest.

Under continuous human disturbance, regeneration is the basis for biodiversity persistence and ecosystem service provision. In tropical dry forests, edaphic ecosystem engineering by biological soil crusts (biocrusts) could impact regeneration by influencing erosion control and soil water and nutrient fluxes, which impact landscape hydrology, geomorphology, and ecosystem functioning. This study investigated the effect of cyanobacteria-dominated biocrusts on water infiltration and aggregate stability in a human-modified landscape of the Caatinga dry forest (NE Brazil), a system characterized by high levels of forest degradation and increasing aridity. By trapping dust and swelling of cyanobacterial filaments, biocrusts can seal soil surfaces and slow down infiltration, which potentially induces erosion. To quantify hydraulic properties and erosion control, we used minidisc-infiltrometry, raindrop-simulation, and wet sieving at two sites with contrasting disturbance levels: an active cashew plantation and an abandoned field experiencing forest regeneration, both characterized by sandy soils. Under disturbance, biocrusts had a stronger negative impact on infiltration (reduction by 42% vs. 37% during regeneration), although biocrusts under regenerating conditions had the lowest absolute sorptivity (0.042 ± 0.02 cm s-1/2) and unsaturated hydraulic conductivity (0.0015 ± 0.0008 cm s-1), with a doubled water repellency. Biocrusts provided high soil aggregate stability although stability increased considerably with progression of biocrust succession (raindrop simulation disturbed: 0.19 ± 0.22 J vs. regenerating: 0.54 ± 0.22 J). The formation of stable aggregates by early successional biocrusts on sandy soils suggests protection of dry forest soils even on the worst land use/soil degradation scenario with a high soil erosion risk. Our results confirm that biocrusts covering bare interspaces between vascular plants in human-modified landscapes play an important role in surface water availability and erosion control. Biocrusts have the potential to reduce land degradation, but their associated ecosystem services like erosion protection, can be impaired by disturbance. Considering an average biocrust coverage of 8.1% of the Caatinga landscapes, further research should aim to quantify the contribution of biocrusts to forest recovery to fully understand the role they play in the functioning of this poorly explored ecosystem.

Arbuscular mycorrhizal symbiosis enhances water stable aggregate formation and organic matter stabilization in Fe ore tailings

Organo-mineral association and water-stable aggregation in finely textured tailings are critically important to the eco-engineered soil formation from alkaline Fe ore tailings for sustainable mine site rehabilitation. Arbuscular mycorrhizal (AM) symbiosis plays important roles in soil aggregate formation and organic matter (OM) stabilization. However, it is unknown if AM symbiosis could enhance aggregate formation and OM stabilization in alkaline Fe ore tailings. The present study aimed to investigate the establishment of AM symbiosis and their role in tailing aggregate formation coupled with OM stabilization, as well as the underlying mechanisms. After initial eco-engineering (OM amendment and pioneer plant cultivation) to improve physicochemical conditions for plant survival, Sorghum spp. Hybrid cv. Silk inoculated with/without AM fungi (Glomus spp.) were cultivated in the tailings under glasshouse conditions for 14 weeks. The results indicated that AM fungi formed symbiotic association with Sorghum spp. plants, improved mineral nutrient (e.g., P) acquisition and root growth in the eco-engineered tailings. The AM symbiosis significantly improved aggregate formation. The association of organic carbon and nitrogen with tailing minerals of the aggregates was enhanced by the AM symbiosis. As revealed by synchrotron-based C 1 s near edge X-ray absorption fine structure (C 1 s NEXAFS) and Fe K edge X-ray absorption fine structure (Fe K edge XAFS) spectroscopy, the AM symbiosis favoured carboxyl and aromatic C association with secondary Fe-Si minerals, which may have been formed from AM driven mineral weathering. Overall, the study revealed that the AM symbiosis could not only improve the growth of pioneer plant species in the early eco-engineered tailings, but also advance soil formation through enhancing organic C and N sequestration and physical structure development via water-stable aggregation. These findings help to advance our understanding of the importance of AM symbiosis in the eco-engineering of tailings into functional soil (or technosols) for sustainable rehabilitation of Fe-ore tailings.

Nano-assembly and optical properties of difluoroboron dibenzoylmethane-polysilane

Aggregation of various fluorophores is a useful approach to build highly sensitive and selective fluorescent sensors. In this work, the ability of oligomeric polydiphenylsilanes to associate with fluorescent low molecular weight organic compound is illustrated by the formation of stable aggregates between poly[diphenyl-co-methyl(H)]silane and dibenzoylmethanatoboron difluoride in solution. The formation of these nano-structures in solution was investigated both experimentally using gel permeation chromatography, σ spectroscopy and fluorescence spectroscopy, and theoretically by molecular modeling. Thin films obtained from this solution have a characteristic morphology in which the nano-aggregates undergo a self-organizing process and form crystalline spherulites. Association between the fluorescent polysilane and the fluorescent diketonato boron complex proceeds with an increase of fluorescence (amplification efficiency up to 90%) through a FRET mechanism as a result of aggregation, a phenomenon that could be used in the development of fluorescent sensors.

The influence of surface charge on the coalescence of ice and dust particles in the mesosphere and lower thermosphere

Abstract. Agglomeration of charged ice and dust particles in the mesosphere and lower thermosphere is studied using a classical electrostatic approach, which is extended to capture the induced polarisation of surface charge. Collision outcomes are predicted whilst varying the particle size, charge, dielectric constant, relative kinetic energy, collision geometry and the coefficient of restitution. In addition to Coulomb forces acting on particles of opposite charge, instances of attraction between particles of the same sign of charge are discussed. These attractive forces are governed by the polarisation of surface charge and can be strong at very small separation distances. In the mesosphere and lower thermosphere, these interactions could also contribute to the formation of stable aggregates and contamination of ice particles through collisions with meteoric smoke particles.

Humic-mineral interactions modulated by pH conditions in bauxite residues – Implications in stable aggregate formation

Bauxite residue exhibiting high sodicity, nutrient deficiency, and poor structure, has a very slow effect on natural vegetation. However, it presents some eco-friendly indicators through substrate improvement, which is the basis for bauxite residue to show pedogenesis and vegetation restoration. To test the effectiveness of acid organic materials toward promoting transformation into a soil-like material, bauxite residue was amended with nitrohumic acid to improve the physical and chemical properties. The pH, total alkalinity, and exchangeable sodium percentage of the treated bauxite residues decreased from 10.2, 2.7 cmol/kg, and 20.6% to 8.0, 0.4 cmol/kg, and 5.1%, respectively, whilst organic matter, available N and P increased from 1.3%, 6.7 mg/kg, and 0.8 mg/kg to 7.2%, 69.7 mg/kg, and 2.4 mg/kg, respectively. The results obtained from excitation-emission matrix spectroscopy also indicate that the nitrohumic acid treated residues have a higher fulvic acid content and present a significant amount of humified material and soil maturation. The high alkalinity of bauxite residue promotes the release of hydroxyl and phenolic hydroxyl groups from fulvic acid to combine with cations. Nitrohumic acid neutralization lowered the IEP and PZC to pH 7.83 and 7.79, and made its surface charge properties closer to the soil; the decreased zeta potential of residues resulted in the particles dispersed state tend to aggregate. And as a result, the number of 0.05–0.25 mm and > 0.25 mm aggregates in the treated bauxite residues significantly increased, the sheet-like fine particles adhere to the surface of the large particles resulted in an accumulation and a layer structure formed. Amount of Ca and Fe in the aggregates as an inorganic binder combined with organic to promote the formation of micro-aggregates; whereas the content of Na and Si, which act as a “dispersant” and “filler” decreased.

Exposure of nanoplastics to freeze-thaw leads to aggregation and reduced transport in model groundwater environments

Despite plastic pollution being a significant environmental concern, the impact of environmental conditions such as temperature cycling on the fate of nanoplastics in cold climates remains unknown. To better understand nanoplastic mobility in subsurface environments following freezing and thawing cycles, the transport of 28 nm polystyrene nanoplastics exposed to either constant (10°C) temperature or freeze-thaw (FT) cycles (-10°C to 10°C) was investigated in saturated quartz sand. The stability and transport of nanoplastic suspensions were examined both in the presence and absence of natural organic matter (NOM) over a range of ionic strengths (3-100 mM NaCl). Exposure to 10 FT cycles consistently led to significant aggregation and reduced mobility compared to nanoplastics held at 10°C, especially at low ionic strengths in the absence of NOM. While NOM increased nanoplastic mobility, it did not prevent the aggregation of nanoplastics exposed to FT. We compare our findings with existing literature and show that nanoplastics will largely aggregate and associate with soils rather than undergo long range transport in groundwater in colder climates following freezing temperatures. In fact, FT exposure leads to the formation of stable aggregates that are not prone to disaggregation. As one of the first studies to examine the coupled effect of cold temperature and NOM, this work highlights the need to account for climate and temperature changes when assessing the risks associated with nanoplastic release in aquatic systems.

Formation of stable aggregates by fluid-assembled solid bridges

When a colloidal suspension is dried, capillary pressure may overwhelm repulsive electrostatic forces, assembling aggregates that are out of thermal equilibrium. This poorly understood process confers cohesive strength to many geological and industrial materials. Here we observe evaporation-driven aggregation of natural and synthesized particulates, probe their stability under rewetting, and measure bonding strength using an atomic force microscope. Cohesion arises at a common length scale (∼5 μm), where interparticle attractive forces exceed particle weight. In polydisperse mixtures, smaller particles condense within shrinking capillary bridges to build stabilizing "solid bridges" among larger grains. This dynamic repeats across scales, forming remarkably strong, hierarchical clusters, whose cohesion derives from grain size rather than mineralogy. These results may help toward understanding the strength and erodibility of natural soils, and other polydisperse particulates that experience transient hydrodynamic forces.

P.233 Doxycycline attenuates anxiety and microglia activation induced by repeated lipopolysaccharide

Sodium hyodeoxycholate (NaHDC) is the main component of hog bile salts, which play a role in the absorption of sparingly soluble materials in the intestinal solution. The biosurfactant has an amphiphilic molecular structure, similar to that of ursodeoxycholate from bear gallbladder. Micelle formation from hyodeoxycholate was studied at 308.2 K using pyrene fluorescence probe to determine critical micelle concentrations (cmc) at various NaCl concentrations. The change in the fluorescence spectrum peak ratios with NaHDC concentration indicated two steps for bile salt aggregation. The first step was the formation of small micelles (cmc) at 5 mM, and the second step was the formation of stable aggregates at 14 mM in aqueous solution. The aggregation of hyodeoxycholate, analyzed using the stepwise association model, was found to grow its aggregation number from 4 to 7 with increasing concentration. The aggregation number in aqueous solution was also confirmed by the static light scattering method. The average measured aggregation number of the micelles was 6.7. The micellar size was relatively small as measured by either method, but it was covered by general aggregation number of human bile salts. The degree of counterion binding to the micelles, determined using a sodium ion-selective electrode, was ca. 0.5 for the NaHDC micelles. This value was relatively high among typical bile salts. Moreover, the solubilization capacity of the NaHDC micelles was assessed using cholesterol. It became clear that NaHDC micelles hardly solubilized cholesterol compared to typical human bile salts. The maximum solubilization by NaHDC was equivalent only to that by sodium ursodeoxycholate

Agent-Based Modeling Reveals Possible Mechanisms for Observed Aggregation Cell Behaviors

Myxococcus xanthus is a soil bacterium that serves as a model system for biological self-organization. Cells form distinct, dynamic patterns depending on environmental conditions. An agent-based model was used to understand how M. xanthus cells aggregate into multicellular mounds in response to starvation. In this model, each cell is modeled as an agent represented by a point particle and characterized by its position and moving direction. At low agent density, the model recapitulates the dynamic patterns observed by experiments and a previous biophysical model. To study aggregation at high cell density, we extended the model based on the recent experimental observation that cells exhibit biased movement toward aggregates. We tested two possible mechanisms for this biased movement and demonstrate that a chemotaxis model with adaptation can reproduce the observed experimental results leading to the formation of stable aggregates. Furthermore, our model reproduces the experimentally observed patterns of cell alignment around aggregates.

Changes in distribution and microstructure of bauxite residue aggregates following amendments addition

Bauxite residue is a highly alkaline byproduct which is routinely discarded at residue disposal areas. Improving soil formation process to revegetate the special degraded lands is a promising strategy for sustainable management of the refining industry. A laboratory incubation experiment was used to evaluate the effects of gypsum and vermicompost on stable aggregate formation of bauxite residue. Aggregate size distribution was quantified by fractal theory, whilst residue microstructure was determined by scanning electron microscopy and synchrotron-based X-ray micro-computed tomography. Amendments addition increased the content of macro-aggregates (>250 μm) and enhanced aggregate stability of bauxite residue. Following gypsum and vermicompost addition, fractal dimension decreased from 2.84 to 2.77, which indicated a more homogeneous distribution of aggregate particles. Images from scanning electron microscopy and three-dimensional microstructure demonstrated that amendments stimulate the formation of improved structure in residue aggregates. Pore parameters including porosity, pore throat surface area, path length, and path tortuosity increased under amendment additions. Changes in aggregate size distribution and microstructure of bauxite residue indicated that additions of gypsum and vermicompost were beneficial to physical condition of bauxite residue which may enhance the ease of vegetation.

Molecular insights into sodium dodecyl sulphate mediated control of size for silver nanoparticles

A specific condition directing the formation of silver nanoparticles (AgNPs) with narrow size-distribution in aqueous sodium dodecyl sulphate (SDS) solutions, using trisodium citrate (TSC) is investigated. The peculiar control in distribution of size for AgNPs in presence of 35 mM (~1 wt%) aqueous SDS solution as stabilizing agent is evident. Water penetration through packed PTFE powder and dynamic surface tension measurements demonstrate formation of stable aggregates at the given condition and accordingly reduced numbers of free SDS monomers diffusing to the growing AgNP interface. The smaller size of AgNPs was also confirmed by TEM images, which illustrates mixed morphologies for the nanoparticles in an aggregated state. The NMR experiments reveal strong hydrophobic interactions between the alkyl chains of SDS molecules adsorbed on AgNPs. These results also indicate that TSC is molecularly distributed in bulk phase without binding to the SDS micellar aggregates. A plausible molecular mechanism is proposed based on diffusion of Ag+ ions to the growing AgNP surface along with SDS monomers and submicellar aggregates, subsequently forming bigger size AgNPs. The narrow distribution of size for AgNP in presence of 35 mM SDS is arguably driven by the capping of stable SDS micelles or monomers around growing nuclei and restricted number of SDS monomers and submicellar aggregates responsible for supply of Ag+ at the growing AgNP nuclei.

Effect of organic amendment for the construction of favourable urban soils for tree growth

Ornamental tree planting and establishment in cities is a great challenge because urban soil physical properties are unfavourable to the development of root systems. Our objectives were to measure (i) the effects of organic matter on soil physical properties and tree development, and (ii) the effects of ensuing root development on soil physical properties. Using twenty-four 600-L planted or bare soil containers, we monitored physical properties such as dry bulk density, aggregate stability and near-saturated hydraulic conductivity of our reconstituted soils over a 5.5-year period. A 28-cm thick top layer of sandy loam amended with 40% (v/v) sphagnum peat or organic composts was laid on top of a 28-cm thick layer of sandy loam. Bare-root Ostrya carpinifolia trees were planted in half of the 24 containers, and we monitored shoot development and root biomass and distribution. After 5.5 years, trunk diameter had increased from 59 mm for the control soil to 66 mm for soil mixed with green waste compost, and 74 mm for soil mixed with co-compost of sewage sludge and wood chips. After 4.5 years, trunk diameter was strongly correlated with the total number of axes (r = 0.94) and fine root length density (r = 0.98), and was confirmed as a good indicator of tree development. Fine root development increased stable aggregate formation in all treatments as compared to bare soil. After 4.5 years after planting, the tree root system induced by a high organic matter input had significantly improved near-saturated hydraulic conductivity and was fit to support fertile urban soils.

Making Milk Less Allergenic

The formation of stable aggregates by food proteins is associated with allergenicity. In particular, amyloid formation by the fish allergen parvalbumin was recently shown to favor IgE binding and subsequent allergic recognition. Therefore, reducing amyloid content in an allergenic food might offer a direct way to make that food less likely to trigger an allergy. In this project, protein aggregation and amyloid formation were studied in milk using gel electrophoresis and fluorescence-based assays. The results suggested that ordinary pasteurized milk from the grocery store contained protein aggregates and specifically amyloid. Processing the milk as normally done during food preparation did not appreciably affect general aggregation or amyloid formation. However, the addition of some polyphenol-containing food products to the milk appeared to result in reduced amyloid levels. Moreover, cranberry juice also appeared to reduce amyloid formation by the milk protein casein. These results suggest that the addition of cranberry or other polyphenol-rich foods to milk products for young children may reduce the risk of milk allergy development by diminishing protein aggregation.

Selective Recognition of Fluoride by using a Benzobisimidazolium Derivative through Aggregation‐Induced Fluorescence

A new benzobisimidazolium derivative (1) bearing four naphthalene moieties was synthesized and demonstrated as an F− ion‐selective fluorescent chemosensor. The fluorescence of 1 in acetonitrile (CH3CN) is significantly stronger with F− and acetate (CH3CO2 −), but not with other anions (Cl−, Br−, I−, HSO4 −, and H2PO4 −). The fluorescence of 1 is enhanced selectively with F− in the presence of a small amount of water. Our DFT calculations indicate that the electrostatic interactions between the positively charged benzobisimidazolium moieties and F− play an important role in the formation of stable aggregates. The formation of stable aggregates of 1 with F− in CH3CN is a key step for the selective sensing of F−, and the fluorescence of the aggregates is further enhanced in a mixture of 95 % CH3CN and 5 % water, which can be attributed to the aggregation‐induced emission.

Aggregation and innate immune response modulating impurities

Abstract Therapeutic proteins can induce immune responses that affect the safety and efficacy even if derived from human sequences. The factors that contribute to the immunogenicity of this therapeutics are poorly understood, but protein aggregation is thought to facilitate it. Previously, our lab showed that trace levels of product or process derived innate immune response modulating impurities (IIRMIs) can also increase product immunogenicity. In this study we hypothesized that protein aggregates and IIRMIs may synergize to facilitate product immunogenicity and explored it using clinical grade Human Serum Albumin (HSA) and Intravenous Immunoglobulin (IVIG) proteins as model. Protein aggregations formed by mechanical stress (shaking and stirring) were characterized by SDS-PAGE, turbidity, MFI and FlowCAM. Cellular responses to aggregated proteins with trace levels of IIRMs were tested in human PBMC. We show that stirring and shaking resulted in the formation of stable aggregates with size ranges of 2 – 50 μm for stirred HSA; and 2–100 μm for IVIG. Despite the similarity in size, the functional assays showed that aggregates of IVIG result in increased mRNA expression of IL-8, IL-6, IL-1β and CCL-2 whereas HSA aggregates did not. Further, we analyzed how the aggregated product changed the transcriptome using Nanostring and showed that aggregated IVIG (shaken or stirred) significantly increased the mRNA of CCL2, CCL7, CCL3, CCL24, CSF1, CXCL2, IRAK1, EGR2, CEBPβ, PPARg, TNFSF15 and whereas HSA aggregates did not. Similarly MAPKs (pp38, pERK and pJNK) and pAKT were activated when PBMC were stimulated with IVIG aggregates but not HSA aggregates. Lastly, we examined whether the effect was mediated by Toll like receptors.

Stationary patterns and their selection mechanism of urban crime models with heterogeneous near-repeat victimization effect

In this paper, we study two PDEs that generalize the urban crime model proposed by Short et al. (2008 Math. Models Methods Appl. Sci.18, 1249–1267). Our modifications are made under assumption of the spatial heterogeneity of both the near-repeat victimization effect and the dispersal strategy of criminal agents. We investigate pattern formations in the reaction–advection–diffusion systems with non-linear diffusion over multi-dimensional bounded domains subject to homogeneous Neumann boundary conditions. It is shown that the positive homogeneous steady state loses its stability as the intrinsic near-repeat victimization rate ε decreases and spatially inhomogeneous steady states emerge through bifurcation. Moreover, we find the wavemode selection mechanism through rigorous stability analysis of these non-trivial spatial patterns, which shows that the only stable pattern must have a wavenumber that maximizes the bifurcation value. Based on this wavemode selection mechanism, we will be able to predict the formation of stable aggregates of the house attractiveness and criminal population density, at least when the diffusion rate ε is around the principal bifurcation value. Our theoretical results also suggest that large domains support more stable aggregates than small domains. Finally, we perform extensive numerical simulations over 1D intervals and 2D squares to illustrate and verify our theoretical findings. Our numerics also demonstrate the formation of other interesting patterns in these models such as the merging of two interior spikes and the emerging of new spikes, etc. These non-trivial solutions can model the well-observed phenomenon of aggregation in urban criminal activities.

Anti-Prion Ligand Binding Promotes Native PrP Folding Over Misfolding at the Single Molecule Level

Ligands that bind to the prion protein, PrP, and prevent the spread of the diseased state have been discovered, but their mechanism of action remains uncertain. Determining anti-prion mechanisms may provide insight into the still-unknown means by which native PrP is converted to the infectious form. To explore the effects of an anti-prion ligand at the molecular level, we used force spectroscopy to study how a tetrapyrrole known to have anti-prion activity, iron(III)meso-tetra(N-methyl-4-pyridyl-prophine) or Fe-TMPyP, alters the folding behavior of individual PrP molecules. Single PrP molecules were unfolded using optical tweezers in the presence and absence of Fe-TMPyP. Ligand binding to the native structure was found to significantly increase its unfolding force. Not only did Fe-TMPyP binding stabilize the native state as expected from ensemble binding studies, but analysis of the unfolding force distributions revealed that Fe-TMPyP binding altered the nature of the transition state for unfolding the native structure: the energy barrier moved closer to the native state, making the transition state more compact, and the barrier height increased. Unexpectedly, Fe-TMPyP was also able to bind to PrP when it was unfolded or only partially folded, thereby delaying the normally rapid refolding into the native state. Probing the effects of Fe-TMPyP on inter-molecular interactions by measuring PrP dimers revealed that ligand binding promoted the formation of the native structure in individual monomers, preventing the formation of a thermodynamically-stable misfolded dimeric state. The ligand thus promotes native folding by stabilizing the native state while at the same time suppressing interactions that drive the formation of stable aggregates. These results suggest parallels between pharmacological chaperones like Fe-TMPyP and cellular chaperones.