15 research outputs found
The Structure-Function Relationship of PAMAM Dendrimers as Robust Oil Dispersants
PAMAM dendrimers have recently been investigated as efficient and biocompatible oil dispersants utilizing their encapsulation capacity; however, their high cationic charge density has been shown to be cytotoxic. It is therefore imperative to mitigate cationic charge-induced toxicity and understand the effects of such changes. Presented here is a synergistic experimental and computational approach to examine the effects of varying terminal surface charge on the capacity of dendrimers to disperse model liner, polycyclic aromatic, and hybrid hydrocarbons. Uncharged dendrimers collapse by forming intramolecular hydrogen bonds, which reduce the hosting capability. On the other hand, changing the surface charges from positive to negative greatly shifts the pKa of tertiary amines of the PAMAM dendrimer interior. As a result, the negatively charged dendrimers have a significant percentage of tertiary amines protonated, âŒ30%. This unexpected change in the interior protonation state causes electrostatic interactions with the anionic terminal groups, leading to contraction and a marked decrease in hydrocarbon hosting capacity. The present work highlights the robust nature of dendrimer oil dispersion and also illuminates potentially unintended or unanticipated effects of varying dendrimer surface chemistry on their encapsulation or hosting efficacy, which is important for their environmental, industrial, and biomedical applications
Direct observation of a single nanoparticleâubiquitin corona formation
The advancement of nanomedicine and the increasing applications of nanoparticles in consumer products have led to administered biological exposure and unintentional environmental accumulation of nanoparticles, causing concerns over the biocompatibility and sustainability of nanotechnology. Upon entering physiological environments, nanoparticles readily assume the form of a nanoparticle-protein corona that dictates their biological identity. Consequently, understanding the structure and dynamics of nanoparticle-protein corona is essential for predicting the fate, transport, and toxicity of nanomaterials in living systems and for enabling the vast applications of nanomedicine. Here we combined multiscale molecular dynamics simulations and complementary experiments to characterize the silver nanoparticle-ubiquitin corona formation. Notably, ubiquitins competed with citrates for the nanoparticle surface, governed by specific electrostatic interactions. Under a high protein/nanoparticle stoichiometry, ubiquitins formed a multi-layer corona on the particle surface. The binding exhibited an unusual stretched-exponential behavior, suggesting a rich binding kinetics. Furthermore, the binding destabilized the α-helices while increasing the ÎČ-sheets of the proteins. This study revealed the atomic and molecular details of the structural and dynamic characteristics of nanoparticle-protein corona formation
Engineered Nanoparticles Interact with Nutrients to Intensify Eutrophication in a Wetland Ecosystem Experiment
Despite the rapid rise in diversity and quantities of engineered nanomaterials produced, the impacts of these emerging contaminants on the structure and function of ecosystems have received little attention from ecologists. Moreover, little is known about how manufactured nanomaterials may interact with nutrient pollution in altering ecosystem productivity, despite the recognition that eutrophication is the primary water quality issue in freshwater ecosystems worldwide. In this study, we asked two main questions: (1) To what extent do manufactured nanoparticles affect the biomass and productivity of primary producers in wetland ecosystems? (2) How are these impacts mediated by nutrient pollution? To address these questions, we examined the impacts of a citrateâcoated gold nanoparticle (AuNPs) and of a commercial pesticide containing Cu(OH)2 nanoparticles (CuNPs) on aquatic primary producers under both ambient and enriched nutrient conditions. Wetland mesocosms were exposed repeatedly with low concentrations of nanoparticles and nutrients over the course of a 9âmonth experiment in an effort to replicate realistic field exposure scenarios. In the absence of nutrient enrichment, there were no persistent effects of AuNPs or CuNPs on primary producers or ecosystem productivity. However, when combined with nutrient enrichment, both NPs intensified eutrophication. When either of these NPs were added in combination with nutrients, algal blooms persisted for \u3e 50 d longer than in the nutrientâonly treatment. In the AuNP treatment, this shift from clear waters to turbid waters led to large declines in both macrophyte growth and rates of ecosystem gross primary productivity (average reduction of 52% ± 6% and 92% ± 5%, respectively) during the summer. Our results suggest that nutrient status greatly influences the ecosystemâscale impact of two emerging contaminants and that synthetic chemicals may be playing an underâappreciated role in the global trends of increasing eutrophication. We provide evidence here that chronic exposure to Au and Cu(OH)2 nanoparticles at low concentrations can intensify eutrophication of wetlands and promote the occurrence of algal blooms
Competitive binding of natural amphiphiles with graphene derivatives
Understanding the transformation of graphene derivatives by natural amphiphiles is essential for elucidating the biological and environmental implications of this emerging class of engineered nanomaterials. Using rapid discrete-molecular-dynamics simulations, we examined the binding of graphene and graphene oxide with peptides, fatty acids and cellulose and complemented our simulations by experimental studies of Raman spectroscopy, FTIR and UV-Vis spectrophotometry. Specifically, we established a connection between the differential binding and the conformational flexibility, molecular geometry and hydrocarbon content of the amphiphiles. Importantly, our dynamics simulations revealed a Vroman-like competitive binding of the amphiphiles for the graphene oxide substrate. This study provides a mechanistic basis for addressing the transformation, evolution, transport, biocompatibility and toxicity of graphene derivatives in living systems and the natural environment
Nanoparticle Surface Affinity as a Predictor of Trophic Transfer
Nanoscale materials, whether natural, engineered, or incidental,
are increasingly acknowledged as important components in large, environmental
systems with potential implications for environmental impact and human
health. Mathematical models are a useful tool for handling the rapidly
increasing complexity and diversity of these materials and their exposure
routes. Presented here is a mathematical model of trophic transfer
driven by nanomaterial surface affinity for environmental and biological
surfaces, developed in tandem with an experimental functional assay
for determining these surface affinities. We found that nanoparticle
surface affinity is a strong predictor of uptake through predation
in a simple food web consisting of the algae Chlorella
vulgaris and daphnid Daphnia magna. The mass of nanoparticles internalized by D. magna through consuming nanomaterial-contaminated algae varied linearly
with surface-attachment efficiency. Internalized quantities of gold
nanoparticles in D. magna ranged from
8.3 to 23.6 ng/mg for nanoparticle preparations with surface-attachment
efficiencies ranging from 0.07 to 1. This model, coupled with the
functional-assay approach, may provide a useful screening tool for
existing materials as well as a predictive model for their development
PAMAM Dendrimers and Graphene: Materials for Removing Aromatic Contaminants from Water
We present results
from experiments and atomistic molecular dynamics
simulations on the remediation of naphthalene by polyamidoamine (PAMAM)
dendrimers and graphene oxide (GrO). Specifically, we investigate
3<sup>rd</sup>â6<sup>th</sup> generation (G3-G6) PAMAM dendrimers
and GrO with different levels of oxidation. The work is motivated
by the potential applications of these emerging nanomaterials in removing
polycyclic aromatic hydrocarbon contaminants from water. Our experimental
results indicate that GrO outperforms dendrimers in removing naphthalene
from water. Molecular dynamics simulations suggest that the prominent
factors driving naphthalene association to these seemingly disparate
materials are similar. Interestingly, we find that cooperative interactions
between the naphthalene molecules play a significant role in enhancing
their association to the dendrimers and GrO. Our findings highlight
that while selection of appropriate materials is important, the interactions
between the contaminants themselves can also be important in governing
the effectiveness of a given material. The combined use of experiments
and molecular dynamics simulations allows us to comment on the possible
factors resulting in better performance of GrO in removing polyaromatic
contaminants from water
Measuring Nanoparticle Attachment Efficiency in Complex Systems
As
process-based environmental fate and transport models for engineered
nanoparticles are developed, there is a need for relevant and reliable
measures of nanoparticle behavior. The affinity of nanoparticles for
various surfaces (α) is one such measure. Measurements of the
affinity of nanoparticles obtained by flowing particles through a
porous medium are constrained by the types of materials or exposure
scenarios that can be configured into such column studies. Utilizing
glass beads and kaolinite as model collector surfaces, we evaluate
a previously developed mixing method for measuring nanoparticle attachment
to environmental surfaces, and validate this method with an equivalent
static column system over a range of organic matter concentrations
and ionic strengths. We found that, while both impacted heteroaggregation
rates in a predictable manner when varied individually, neither dominated
when both parameters were varied. The theory behind observed nanoparticle
heteroaggregation rates (αÎČB) to background particles
in mixed systems is also experimentally validated, demonstrating both
collision frequency (ÎČ) and background particle concentration
(B) to be independent for use in fate modeling. We further examined
the effects of collector particle composition (kaolinite vs glass
beads) and nanoparticle surface chemistry (PVP, citrate, or humic
acid) on α, and found a strong dependence on both