Oxide- and Silicate-Water Interfaces and Their Roles in Technology and the Environment.

Interfacial reactions drive all elemental cycling on Earth and play pivotal roles in human activities such as agriculture, water purification, energy production and storage, environmental contaminant remediation, and nuclear waste repository management. The onset of the 21st century marked the beginning of a more detailed understanding of mineral aqueous interfaces enabled by advances in techniques that use tunable high-flux focused ultrafast laser and X-ray sources to provide near-atomic measurement resolution, as well as by nanofabrication approaches that enable transmission electron microscopy in a liquid cell. This leap into atomic- and nanometer-scale measurements has uncovered scale-dependent phenomena whose reaction thermodynamics, kinetics, and pathways deviate from previous observations made on larger systems. A second key advance is new experimental evidence for what scientists hypothesized but could not test previously, namely, interfacial chemical reactions are frequently driven by "anomalies" or "non-idealities" such as defects, nanoconfinement, and other nontypical chemical structures. Third, progress in computational chemistry has yielded new insights that allow a move beyond simple schematics, leading to a molecular model of these complex interfaces. In combination with surface-sensitive measurements, we have gained knowledge of the interfacial structure and dynamics, including the underlying solid surface and the immediately adjacent water and aqueous ions, enabling a better definition of what constitutes the oxide- and silicate-water interfaces. This critical review discusses how science progresses from understanding ideal solid-water interfaces to more realistic systems, focusing on accomplishments in the last 20 years and identifying challenges and future opportunities for the community to address. We anticipate that the next 20 years will focus on understanding and predicting dynamic transient and reactive structures over greater spatial and temporal ranges as well as systems of greater structural and chemical complexity. Closer collaborations of theoretical and experimental experts across disciplines will continue to be critical to achieving this great aspiration.

New Insights into Calcite Dissolution Mechanisms under Water, Proton, or Carbonic Acid-Dominated Conditions.

Carbonate minerals are ubiquitous in nature, and their dissolution impacts many environmentally relevant processes including preferential flow during geological carbon sequestration, pH buffering with climate-change induced ocean acidification, and organic carbon bioavailability in melting permafrost. In this study, we advance the atomic level understanding of calcite dissolution mechanisms to improve our ability to predict this complex process. We performed high pressure and temperature (1300 psi and 50 °C) batch experiments to measure transient dissolution of freshly cleaved calcite under H2O, H+, and H2CO3-dominated conditions, without and with an inhibitory anionic surfactant present. Before and after dissolution experiments, we measured dissolution etch-pit geometries using laser profilometry, and we used density functional theory to investigate relative adsorption energies of competing species that affect dissolution. Our results support the hypothesis that calcite dissolution is controlled by the ability of H2O to preferentially adsorb to surface Ca atoms over competing species, even when dissolution is dominated by H+ or H2CO3. More importantly, we identify for the first time that adsorbed H+ enhances the role of water by weakening surface Ca-O bonds. We also identify that H2CO3 undergoes dissociative adsorption resulting in adsorbed HCO3- and H+. Adsorbed HCO3- that competes with H2O for Ca acute edge sites inhibits dissolution, while adsorbed H+ at the neighboring surface of CO3 enhances dissolution. The net effect of the dissociative adsorption of H2CO3 is enhanced dissolution. These results will impact future efforts to more accurately model the impact of solutes in complex water matrices on carbonate mineral dissolution.

Affinity of small-molecule solutes to hydrophobic, hydrophilic, and chemically patterned interfaces in aqueous solution.

Performance of membranes for water purification is highly influenced by the interactions of solvated species with membrane surfaces, including surface adsorption of solutes upon fouling. Current efforts toward fouling-resistant membranes often pursue surface hydrophilization, frequently motivated by macroscopic measures of hydrophilicity, because hydrophobicity is thought to increase solute-surface affinity. While this heuristic has driven diverse membrane functionalization strategies, here we build on advances in the theory of hydrophobicity to critically examine the relevance of macroscopic characterizations of solute-surface affinity. Specifically, we use molecular simulations to quantify the affinities to model hydroxyl- and methyl-functionalized surfaces of small, chemically diverse, charge-neutral solutes represented in produced water. We show that surface affinities correlate poorly with two conventional measures of solute hydrophobicity, gas-phase water solubility and oil-water partitioning. Moreover, we find that all solutes show attraction to the hydrophobic surface and most to the hydrophilic one, in contrast to macroscopically based hydrophobicity heuristics. We explain these results by decomposing affinities into direct solute interaction energies (which dominate on hydroxyl surfaces) and water restructuring penalties (which dominate on methyl surfaces). Finally, we use an inverse design algorithm to show how heterogeneous surfaces, with multiple functional groups, can be patterned to manipulate solute affinity and selectivity. These findings, importantly based on a range of solute and surface chemistries, illustrate that conventional macroscopic hydrophobicity metrics can fail to predict solute-surface affinity, and that molecular-scale surface chemical patterning significantly influences affinity-suggesting design opportunities for water purification membranes and other engineered interfaces involving aqueous solute-surface interactions.

Mechanism of monovalent and divalent ion mobility in Nafion membrane: An atomistic simulation study.

Polymer cation exchange membranes (CEMs) are widely used in water treatment processes. The fundamental factors that control the separation and selectivity of cations with different valences in CEMs are not fully understood. In this study, we use atomistic molecular dynamics simulations to investigate the underlying molecular mechanisms that control the mobility of cations with different valences in Nafion membranes. Our results indicate structural differences in binding of monovalent and divalent cations, which gives rise to differences in ion diffusion in Nafion. Monovalent cations are shown to be "territorially" bound, i.e., bound while partially hydrated, to the fixed charge groups whereas divalent cations are shown to be "site" bound, i.e., bound while fully dehydrated, to the charge groups on the polymer. This difference in binding structure gives rise to differences in transport characteristics of cations in Nafion.

Apparent Reactivity of Bromine in Bromochloramine Depends on Synthesis Method: Implicating Bromine Chloride and Molecular Bromine as Important Bromine Species.

The chloramination of bromide containing waters results in the formation of bromine containing haloamines: monobromamine (NH2Br), dibromamine (NHBr2), and bromochloramine (NHBrCl). Many studies have directly shown that bromamines are more reactive than chloramines in oxidation and substitution reactions with organic water constituents because the bromine atom in oxidants is more labile than the chlorine atom. However, similar studies have not been performed with NHBrCl. It has been assumed that NHBrCl has similar reactivity as bromamines with organic constituents in both oxidation and substitution reactions because NHBrCl, like bromamines, rapidly oxidizes N,N-diethyl-p-phenylenediamine. In this study, we examined the reactivity of NHBrCl with phenol red to determine if NHBrCl reacts as readily as bromamines in an isolated substitution reaction. NHBrCl was synthesized two ways to assess whether NHBrCl or the highly reactive intermediates, bromine chloride (BrCl) and molecular bromine (Br2), were responsible for bromine substitution of phenol red. NHBrCl was found to be much less reactive than bromamines with phenol red and that BrCl and Br2 appeared to be the true brominating agents in solutions where NHBrCl is formed. This work highlights the need to reexamine what the true brominating agents are in chloraminated waters containing bromide.

Primary and secondary caregiver depressive symptoms and family functioning following a pediatric cancer diagnosis: an exploration of the buffering hypothesis.

OBJECTIVE: After diagnosis, caregivers of children with cancer, particularly mothers or primary caregivers (PCs), often show elevated depressive symptoms which may negatively impact family functioning. We tested PC and secondary caregiver (SC) depressive symptoms as predictors of family, co-parenting, and marital functioning and whether having a non-depressed SC buffers against potential negative effects of PC depressive symptoms. METHODS: Families (N = 137) were recruited from two major children's hospitals following a diagnosis of pediatric cancer. Caregivers completed self-report measures of depressive symptoms (Center for Epidemiological Studies-Depression Scale; Depression, Anxiety, and Stress Scale) and marital functioning (Dyadic Adjustment Scale) at 1-month post-diagnosis. A subset of families (n = 75) completed videotaped interaction tasks at approximately 3-months post-diagnosis that were coded for family and co-parenting interactions. RESULTS: Higher PC depressive symptoms at 1-month post-diagnosis was associated with higher adaptability and lower conflict in family functioning. PC depressive symptoms were also associated lower dyadic consensus and lower dyadic satisfaction. SC depressive symptoms were not significantly associated with any family/co-parenting/marital functioning variables. Significant interaction analyses suggested that SC depressive symptoms moderated the effect of PC depressive symptoms on family cohesion, withdrawn parenting, and affective expression in the marriage, such that the relationship between PC depressive symptoms and poorer functioning was attenuated when SC depressive symptoms were at low or average levels. CONCLUSIONS: Having a nondepressed SC buffered against negative effects of PC depressive symptoms on certain domains of family, coparenting, and marital functioning. SCs may play a protective role for families of children with cancer.

Role of Carbonate Species on General Acid Catalysis of Bromide Oxidation by Hypochlorous Acid (HOCl) and Oxidation by Molecular Chlorine (Cl2).

Kinetic models for disinfectant decay and disinfection byproduct (DBP) formation are necessary for predicting water quality from the treatment plant to the tap. A kinetic model for conditions relevant to chloramine disinfection of drinking water (pH 6-9 and carbonate-buffered) was developed to simulate incomplete bromide (Br-) oxidation during short prechlorination periods because it is the first step in a complex system of reactions that leads to disinfectant loss and DBP formation. Hypochlorous acid (HOCl+Br-→kHOClHOBr+Cl-) and molecular chlorine (Cl2+Br-+H2O→kCl2HOBr+2Cl-+H+) were the free chlorine species relevant to Br- oxidation, and Cl2 hydrolysis and formation reactions (Cl2+H2O+A-⇌k-4k4HOCl+HA+Cl-) were necessary to accurately simulate Cl2 concentrations instead of assuming equilibrium. Previous work has shown that Br- oxidation by HOCl and Cl2 formation are acid-catalyzed and Cl2 hydrolysis is base-catalyzed, but the impact of carbonate species had not been studied. This work showed that the carbonate species have an enhanced catalytic impact with rate constants up to 1000 times larger than would be estimated by the Brønsted relationship for similar acids, which causes the oxidation by HOCl rate constant (kHOCl) to nearly double and oxidation by Cl2 to occur above pH 7 in high-alkalinity waters.

Effect of CaCO3(S) Nucleation Modes on Algae Removal from Alkaline Water.

The role of calcite heterogeneous nucleation was studied in a particle-coagulation treatment process for removing microalgae from water. Batch experiments were conducted with Scenedesmus sp. and Chlorella sp. in the presence and absence of carbonate and in the presence and absence of magnesium to delineate the role of CaCO3(S) nucleation on microalgae removal. The results indicate that effective algae coagulation (e.g., up to 81% algae removal efficiency) can be achieved via heterogeneous nucleation with CaCO3(S); however, supersaturation ratios between 120 and 200 are required to achieve at least 50% algae removal, depending on ion concentrations. Algae removal was attributed to the adsorption of Ca2+ onto the cell surface, which provides nucleation sites for CaCO3(S) precipitation. Bridging of calcite particles between the algal cells led to rapid aggregation and formation of larger flocs. However, at higher supersaturation conditions, algae removal was diminished due to the dominance of homogeneous nucleation of CaCO3(S). The removal of algae in the presence of Ca2+ and Mg2+ required higher supersaturation values; however, the shift from heteronucleation to homonucleation with increasing supersaturation was still evident. The results suggest that water chemistry, pH, ionic strength, alkalinity, and Ca2+ concentration can be optimized for algae removal via coagulation and sedimentation.

An intervention that increases parental sensitivity in families referred to Child Protective Services also changes toddlers' parasympathetic regulation.

Experiencing maltreatment in early childhood predicts poor parasympathetic regulation, characterized by low baseline parasympathetic activity and strong withdrawal of parasympathetic influence in response to tasks. The Promoting First Relationships® (PFR) program improves parental sensitivity toward young children in families identified as maltreating. Using a subsample from a randomized control trial, we examined whether parental participation in PFR had lasting effects on toddlers' parasympathetic regulation, as measured by respiratory sinus arrhythmia (RSA), relative to a resource and referral control condition. In addition, we examined whether parental sensitive and responsive behavior mediated or moderated associations between parent treatment group and children's RSA. More than 6 months after completing treatment, 29 families in the PFR condition and 30 families in the control condition were visited at home, and toddlers' RSA was assessed at baseline and during five moderately challenging tasks. Groups did not differ in baseline RSA, but differed in RSA reactivity to the tasks. Across tasks, toddlers of parents in the control condition manifested significantly larger RSA decreases than toddlers of parents in the PFR condition. Parental behavior showed divergent associations with RSA change for toddlers of parents in the PFR versus control condition, with PFR treatment predicting RSA change ranging from small decreases to increases in toddlers of parents who showed the most sensitive, responsive behavior in the 6 months following treatment. This preliminary study showed that the same intervention that improved parenting also improved toddlers' parasympathetic regulation in response to everyday activities, warranting further experimental investigation.

Emotion Reactivity and Regulation in Maltreated Children: A Meta-Analysis.

The many adverse effects of child maltreatment make the scientific investigation of this phenomenon a matter of vital importance. Although the relationship between maltreatment and problematic emotion reactivity and regulation has been studied, the strength and specificity of these associations are not yet clear. We examine the magnitude of the maltreatment-child-emotion reactivity/regulation link. Studies with substantiated maltreatment involving children aged up to 18 were included, along with a smaller number of longitudinal studies (58 papers reviewed, encompassing more than 11,900 children). In comparison to nonmaltreated children, maltreated children experience more negative emotions, behave in a manner indicative of more negative emotion, and display emotion dysregulation. We outline several theoretical implications of our results.

Stress and marital adjustment in families of children with cancer.

OBJECTIVE: Pediatric cancer is highly stressful for parents. The current prospective study examines the impact of several stressors (financial strain, life threat, treatment intensity, treatment-related events, and negative life events) on the trajectory of marital adjustment across the first year following diagnosis. We examined whether average level of stressors across the year was related to (1) levels of marital adjustment at the end of the first year of treatment and () the rate of change in marital adjustment. METHOD: One hundred and thirty families of children newly diagnosed with cancer (M age = 6.33 years, SD = 3.61) participated. Primary caregivers provided 12 monthly reports on marital adjustment and stressors. RESULTS: Multilevel models indicated that although marital adjustment was stable across the first year on average, random effect estimates suggested that this was the result of differing trajectories between families (eg, some increasing and others decreasing). Five individual stress constructs and a cumulative stress composite were then used to predict this variability. Higher average economic strain was related to consistently poorer marital adjustment across time. Higher average frequency of treatment-related events and negative life events were associated with decreasing adjustment over time and lower adjustment at the end of the first year of treatment. Perception of life threat and treatment intensity were not associated with final levels or trajectory of adjustment. Finally, higher cumulative stress was associated with consistently poorer marital adjustment across time. CONCLUSION: Implications for identification of at-risk families are discussed, and importance of delivering tailored interventions for this population.

Patterns of Spillover Between Marital Adjustment and Parent-Child Conflict During Pediatric Cancer Treatment.

Objective: When a child is diagnosed with cancer, problems may arise in family relationships and negatively affect child adjustment. The current study examined patterns of spillover between marital and parent-child relationships to identify targets for intervention aimed at ameliorating family conflict. Method: Families (N = 117) were recruited from two US children's hospitals within 2-week postdiagnosis to participate in a short-term prospective longitudinal study. Children with cancer were 2-10 years old (M = 5.42 years, SD = 2.59). Primary caregivers provided reports of marital and parent-child conflict at 1-, 6-, and 12-month postdiagnosis. Results: Results indicated that a unidirectional model of spillover from the marital to the parent-child relationship best explained the data. In terms of specific temporal patterns, lower marital adjustment soon after diagnosis was associated with an increase in parent-child conflict 6 months later, though this pattern was not repeated in the latter 6 months of treatment. Conclusion: Targeting problems in marital relationships soon after diagnosis may prevent conflict from developing in the parent-child relationship.

Featured Article: Caregiver Perceptions of Stress and Sibling Conflict During Pediatric Cancer Treatment.

Objective: The current study examined the effect of stress on sibling conflict during the first year of pediatric cancer treatment. Method: Families (N = 103) included a child with cancer (aged 2-17 years, Mage = 6.46, SD = 3.52) and at least one sibling aged <5 years of the child with cancer (Mage = 8.34, SD = 5.61). Primary caregivers completed monthly questionnaires throughout the first year of treatment assessing five sources of stress (i.e., general life, cancer-related, financial, perceived treatment intensity, and life threat) and level of sibling conflict. Using multilevel modeling, we explored the effects of these stressors on conflict both at the within- and between-family levels to examine if changes in stress resulted in concurrent changes in conflict within an individual family, and whether greater average stress affected the trajectory of conflict between families, respectively. Results: At the between-family level, higher average levels of cancer-related stress, general life stress, and financial stress were associated with higher sibling conflict at the end of the first year of treatment. Perceived treatment intensity and life threat were not associated with conflict. No stressors were associated with conflict at the within-family level. Conclusions: During pediatric cancer treatment, some stressors may spill over into family relationships and contribute to increases in sibling conflict.

A thermodynamics-based approach for examining the suitability of cementitious formulations for solidifying and stabilizing coal-combustion wastes.

Cementitious binders are often used to immobilize industrial wastes such as residues of coal combustion. Such immobilization stabilizes wastes that contain contaminants by chemical containment, i.e., by uptake of contaminants into the cementitious reaction products. Expectedly, the release ("leachability") of contaminants is linked to: (i) the stability of the matrix (i.e., its resistance to decomposition on exposure to water), and, (ii) its porosity, which offers a pathway for the intrusion of water and egress of contaminant species. To examine the effects of the matrix chemistry on its suitability for immobilization, an equilibrium thermodynamics-based approach is demonstrated for cementitious formulations based on: ordinary portland cement (OPC), calcium aluminate cement (CAC) and alkali activated fly ash (AFA) binding agents. First, special focus is placed on computing the equilibrium phase assemblages using the bulk reactant compositions as an input. Second, the matrix's stability is assessed by simulating leaching that is controlled by progressive dissolution and precipitation of solids across a range of liquid (leachant)-to-(reaction product) solid (l/s) ratios and leachant pH's; e.g., following the LEAF 1313 and 1316 protocols. The performance of each binding formulation is evaluated based on the: (i) relative ability of the reaction products to chemically bind the contaminant(s), (ii) porosity of the matrix which correlates to its hydraulic conductivity, and, (iii) the extent of matrix degradation that follows leaching and which impact the rate and extent of release of potential contaminants. In this manner, the approach enables rapid, parametric assessment of a wide-range of stabilization solutions with due consideration of the matrix's mineralogy, porosity, and the leaching (exposure) conditions.

Mepolizumab treatment in patients with severe eosinophilic asthma.

BACKGROUND: Some patients with severe asthma have frequent exacerbations associated with persistent eosinophilic inflammation despite continuous treatment with high-dose inhaled glucocorticoids with or without oral glucocorticoids. METHODS: In this randomized, double-blind, double-dummy study, we assigned 576 patients with recurrent asthma exacerbations and evidence of eosinophilic inflammation despite high doses of inhaled glucocorticoids to one of three study groups. Patients were assigned to receive mepolizumab, a humanized monoclonal antibody against interleukin-5, which was administered as either a 75-mg intravenous dose or a 100-mg subcutaneous dose, or placebo every 4 weeks for 32 weeks. The primary outcome was the rate of exacerbations. Other outcomes included the forced expiratory volume in 1 second (FEV1) and scores on the St. George's Respiratory Questionnaire (SGRQ) and the 5-item Asthma Control Questionnaire (ACQ-5). Safety was also assessed. RESULTS: The rate of exacerbations was reduced by 47% (95% confidence interval [CI], 29 to 61) among patients receiving intravenous mepolizumab and by 53% (95% CI, 37 to 65) among those receiving subcutaneous mepolizumab, as compared with those receiving placebo (P<0.001 for both comparisons). Exacerbations necessitating an emergency department visit or hospitalization were reduced by 32% in the group receiving intravenous mepolizumab and by 61% in the group receiving subcutaneous mepolizumab. At week 32, the mean increase from baseline in FEV1 was 100 ml greater in patients receiving intravenous mepolizumab than in those receiving placebo (P=0.02) and 98 ml greater in patients receiving subcutaneous mepolizumab than in those receiving placebo (P=0.03). The improvement from baseline in the SGRQ score was 6.4 points and 7.0 points greater in the intravenous and subcutaneous mepolizumab groups, respectively, than in the placebo group (minimal clinically important change, 4 points), and the improvement in the ACQ-5 score was 0.42 points and 0.44 points greater in the two mepolizumab groups, respectively, than in the placebo group (minimal clinically important change, 0.5 points) (P<0.001 for all comparisons). The safety profile of mepolizumab was similar to that of placebo. CONCLUSIONS: Mepolizumab administered either intravenously or subcutaneously significantly reduced asthma exacerbations and was associated with improvements in markers of asthma control. (Funded by GlaxoSmithKline; MENSA ClinicalTrials.gov number, NCT01691521.).

Bromamine Decomposition Revisited: A Holistic Approach for Analyzing Acid and Base Catalysis Kinetics.

Chloramine chemistry is complex, with a variety of reactions occurring in series and parallel and many that are acid or base catalyzed, resulting in numerous rate constants. Bromide presence increases system complexity even further with possible bromamine and bromochloramine formation. Therefore, techniques for parameter estimation must address this complexity through thoughtful experimental design and robust data analysis approaches. The current research outlines a rational basis for constrained data fitting using Brønsted theory, application of the microscopic reversibility principle to reversible acid or base catalyzed reactions, and characterization of the relative significance of parallel reactions using fictive product tracking. This holistic approach was used on a comprehensive and well-documented data set for bromamine decomposition, allowing new interpretations of existing data by revealing that a previously published reaction scheme was not robust; it was not able to describe monobromamine or dibromamine decay outside of the conditions for which it was calibrated. The current research's simplified model (3 reactions, 17 constants) represented the experimental data better than the previously published model (4 reactions, 28 constants). A final model evaluation was conducted based on representative drinking water conditions to determine a minimal model (3 reactions, 8 constants) applicable for drinking water conditions.

Bioavailability of Fullerene under Environmentally Relevant Conditions: Effects of Humic Acid and Fetal Bovine Serum on Accumulation in Lipid Bilayers and Cellular Uptake.

Carbon fullerene (C60) has emerged at the forefront of nanoscale research and application due to its unique properties. As the production of this nanoparticle rapidly increases, it can be released into natural aquatic environments and can accumulate in biological systems. This research examined the effects of humic acid and fetal bovine serum (FBS), which are ubiquitous in aquatic environments and representative of blood plasma in living organisms, respectively, on bioavailability of fullerene. Bioavailability was investigated using in vitro methods for lipid membrane accumulation and cellular uptake studies. Humic acid and FBS significantly changed the characteristics of fullerene including its particle size and surface charge. The effects of humic acid on lipid accumulation of fullerene depended on the lipid head charge. FBS also significantly decreased the lipid accumulation when positively charged and zwitterionic head groups were present on the lipids, possibly due to the higher steric repulsion of the protein coated nanoparticles. In addition, both humic acid and FBS protein effectively lowered the amounts of fullerene taken up by Caco-2 cells, which are derived from a human colorectal adenocarcinoma and have similar functions to the small intestinal epithelium. Results of this study suggest that surface modification of fullerene by environmentally relevant matrices can significantly affect the biological transport, as well as the possible toxicity of this nanomaterial.

Emotion regulation, internalizing symptoms and somatic complaints in pediatric survivors of acute lymphoblastic leukemia.

OBJECTIVES: This study aimed to examine whether respiratory sinus arrhythmia (RSA)-a physiological index of children's emotion regulation-moderates the relation between cancer diagnosis and internalizing problems in children. METHODS: Participants were twenty-two 7-12-year survivors of acute lymphoblastic leukemia and 20 age-matched controls. RSA was calculated from cardiac interbeat interval using spectral time-series analysis. t-Scores on the Child Behavior Checklist Anxious/Depressed, Withdrawn/Depressed, and Somatic Complaints subscales were computed. RESULTS: Respiratory sinus arrhythmia moderated the relation between diagnostic status and both child somatic complaints and withdrawn/depressed symptoms. The positive association between diagnostic status and somatic complaints was significant for children with low RSA but not significant for children with high RSA. This association was also significant for withdrawn/depressed symptoms. Low RSA was associated with more somatic complaints and withdrawn/depressed symptoms for children with cancer but not for control participants. CONCLUSIONS: Children who have poor emotion regulation abilities may be more vulnerable to the range of stressors associated with the diagnosis, treatment, and survivorship of cancer. Behavioral interventions targeting emotion regulation skills may reduce internalizing symptoms in this population.

Distribution of Fullerene Nanoparticles between Water and Solid Supported Lipid Membranes: Thermodynamics and Effects of Membrane Composition on Distribution.

The distribution coefficient (Klipw) of fullerene between solid supported lipid membranes (SSLMs) and water was examined using different lipid membrane compositions. Klipw of fullerene was significantly higher with a cationic lipid membrane compared to that with a zwitterionic or anionic lipid membrane, potentially due to the strong interactions between negative fullerene dispersions and positive lipid head groups. The higher Klipw for fullerene distribution to ternary lipid mixture membranes was attributed to an increase in the interfacial surface area of the lipid membrane resulting from phase separation. These results imply that lipid composition can be a critical factor that affects bioconcentration of fullerene. Distribution of fullerene into zwitterionic unsaturated lipid membranes was dominated by the entropy contribution (ΔS) and the process was endothermic (ΔH > 0). This result contrasts the partitioning thermodynamics of highly and moderately hydrophobic chemicals indicating that the lipid-water distribution mechanism of fullerene may be different from that of molecular level chemicals. Potential mechanisms for the distribution of fullerene that may explain these differences include adsorption on the lipid membrane surfaces and partitioning into the center of lipid membranes (i.e., absorption).