Implications for new particle formation in air of the use of monoethanolamine in carbon capture and storage.

Alkanolamines are currently being deployed in carbon capture and storage (CCS) technology worldwide, and atmospheric emissions have been found to coincide with locations exhibiting elevated concentrations of methanesulfonic acid (MSA). It is thus critical to understand the fate and potential atmospheric reactions of these chemicals. This study reports the characterization of sub-10 nm nanoparticles produced through the acid-base reaction between gas phase monoethanolamine (MEA) and MSA, a product of organosulfur compound oxidation in air, using a flow reactor under dry and humid (up to ∼60% RH) conditions. Number size distribution measurements show that MEA is even more efficient than methylamine in forming nanoparticles on reaction with MSA. This is attributed to the fact that the MEA structure contains both an -NH2 and an -OH group that facilitate hydrogen bonding within the clusters, in addition to the electrostatic interactions. Due to this already strong H-bond network, water has a relatively small influence on new particle formation (NPF) and growth in this system, in contrast to MSA reactions with alkylamines. Acid/base molar ratios of unity for 4-12 nm particles were measured using thermal desorption chemical ionization mass spectrometry. The data indicate that reaction of MEA with MSA may dominate NPF under some atmospheric conditions. Thus, the unique characteristics of alkanolamines in NPF must be taken into account for accurate predictions of impacts of CCS on visibility, health and climate.

Top-down versus bottom-up oxidation of a neonicotinoid pesticide by OH radicals.

Emerging contaminants (EC) distributed on surfaces in the environment can be oxidized by gas phase species (top-down) or by oxidants generated by the underlying substrate (bottom-up). One class of EC is the neonicotinoid (NN) pesticides that are widely distributed in air, water, and on plant and soil surfaces as well as on airborne dust and building materials. This study investigates the OH oxidation of the systemic NN pesticide acetamiprid (ACM) at room temperature. ACM on particles and as thin films on solid substrates were oxidized by OH radicals either from the gas phase or from an underlying TiO2 or NaNO2 substrate, and for comparison, in the aqueous phase. The site of OH attack is both the secondary >CH2 group as well as the primary -CH3 group attached to the tertiary amine nitrogen, with the latter dominating. In the case of top-down oxidation of ACM by gas phase OH radicals, addition to the -CN group also occurs. Major products are carbonyls and alcohols, but in the presence of sufficient water, their hydrolyzed products dominate. Kinetics measurements show ACM is more reactive toward gas phase OH radicals than other NN nitroguanidines, with an atmospheric lifetime of a few days. Bottom-up oxidation of ACM on TiO2 exposed to sunlight outdoors (temperatures were above 30 °C) was also shown to occur and is likely to be competitive with top-down oxidation. These findings highlight the different potential oxidation processes for EC and provide key data for assessing their environmental fates and toxicologies.

Peroxides on the Surface of Organic Aerosol Particles Using Matrix-Assisted Ionization in Vacuum (MAIV) Mass Spectrometry.

Organic peroxides are key intermediates in the atmosphere but are challenging to detect, especially in the particle phase, due to their instability, which has led to substantial gaps in the understanding of their environmental effects. We demonstrate that matrix-assisted ionization in vacuum (MAIV) mass spectrometry (MS), which does not require an ionization source, enables in situ characterization of peroxides and other products in the surface layers of organic particles. Hydroxyl radical oxidation of glutaric acid particles yields hydroperoxides and organic peroxides, which were detected with signals of the same order of magnitude as the major, more stable products. Product identification is supported by MS/MS analysis, peroxide standards, and offline high-resolution MS. The peroxide signals relative to the stable carbonyl and alcohol products are significantly larger using MAIV compared to those in the offline bulk analysis. This is also the case for analysis using fast, online easy ambient sonic-spray ionization mass spectrometry. These studies demonstrate the advantage of MAIV for the real-time characterization of labile peroxides in the surface layers of solid particles. The presence of peroxides on the surface may be important for surface oxidation processes as well as for the toxicity of inhaled particles.

Cueing natural event boundaries improves memory in people with post-traumatic stress disorder.

People with post-traumatic stress disorder (PTSD) often report difficulty remembering information in their everyday lives. Recent findings suggest that such difficulties may be due to PTSD-related deficits in parsing ongoing activity into discrete events, a process called event segmentation. Here, we investigated the causal relationship between event segmentation and memory by cueing event boundaries and evaluating its effect on subsequent memory in people with PTSD. People with PTSD (n = 38) and trauma-matched controls (n = 36) watched and remembered videos of everyday activities that were either unedited, contained visual and auditory cues at event boundaries, or contained visual and auditory cues at event middles. PTSD symptom severity varied substantial within both the group with a PTSD diagnosis and the control group. Memory performance did not differ significantly between groups, but people with high symptoms of PTSD remembered fewer details from the videos than those with lower symptoms of PTSD. Both those with PTSD and controls remembered more information from the videos in the event boundary cue condition than the middle cue or unedited conditions. This finding has important implications for translational work focusing on addressing everyday memory complaints in people with PTSD.

Predicting the environmental fates of emerging contaminants: Synergistic effects in ozone reactions of nitrogen-containing alkenes.

While nitro and amino alkenes are common in pharmaceuticals, pesticides, and munitions, their environmental fates are not well known. Ozone is a ubiquitous atmospheric oxidant for alkenes, but the synergistic effects of nitrogen-containing groups on the reactions have not been measured. The kinetics and products of ozonolysis of a series of model compounds with different combinations of these functional groups have been measured in the condensed phase using stopped-flow and mass spectrometry methods. Rate constants span about six orders of magnitude with activation energies ranging from 4.3 to 28.2 kJ mol-1. Vinyl nitro groups substantially decrease the reactivity, while amino groups have the opposite effect. The site of the initial ozone attack is highly structure dependent, consistent with local ionization energy calculations. The reaction of the neonicotinoid pesticide nitenpyram, which forms toxic N-nitroso compounds, was consistent with model compounds, confirming the utility of model compounds for assessing environmental fates of these emerging contaminants.

Gas Phase and Gas-Solid Interface Ozonolysis of Nitrogen Containing Alkenes: Nitroalkenes, Enamines, and Nitroenamines.

Emerging contaminants are of concern due to their rapidly increasing numbers and potential ecological and human health effects. In this study, the synergistic effects of the presence of multifunctional nitro, amino and carbon-carbon double bond (C═C) groups on the gas phase ozonolysis in O2 or at the air/solid interface were investigated using five simple model compounds. The gas phase ozonolysis rate constants at 296 K were (3.5 ± 0.9) × 10-20 cm3 molecule-1 s-1 for 2-methyl-1-nitroprop-1-ene and (6.8 ± 0.8) × 10-19 cm3 molecule-1 s-1 for 4-methyl-4-nitro-1-pentene, with lifetimes of 134 and 7 days in the presence of 100 ppb ozone in the atmosphere, respectively. The rate constants for gas phase E-N,N-dimethyl-1-propenylamine and N,N-dimethylallylamine reactions with ozone were too fast (>10-18 cm3 molecule-1 s-1) to be measured, implying lifetimes of less than 5 days. A multiphase kinetics model (KM-GAP) was used to probe the gas-solid kinetics of 1-dimethylamino-2-nitroethylene, yielding a rate constant for the surface reaction of 1.8 × 10-9 cm2 molecule-1 s-1 and in the bulk 1× 10-16 cm3 molecule-1 s-1. These results show that a nitro group attached to the C═C lowers the gas phase rate constant by 2-3 orders of magnitude compared to the simple alkenes, while amino groups have the opposite effect. The presence of both groups provides counterbalancing effects. Products with deleterious health effects including dimethylformamide and formaldehyde were identified by FTIR. The identified products differentiate whether the initial site of ozone attack is C═C and/or the amino group. This study provides a basis for predicting the environmental fates of emerging contaminants and shows that both the toxicity of both the parent compounds and the products should be taken into account in assessing their environmental impacts.

PTSD is associated with impaired event processing and memory for everyday events.

Current theories of posttraumatic stress disorder (PTSD) propose that memory abnormalities are central to the development and persistence of symptoms. While the most notable memory disturbances in PTSD involve memory for the trauma itself, individuals often have trouble remembering aspects of everyday life. Further, people with PTSD may have difficulty segmenting ongoing activity into discrete units, which is important for our perception and later memory of the activity. The current study investigated whether PTSD diagnosis and symptom severity predicted event segmentation and memory for everyday activities. To do so, 63 people with PTSD and 64 controls with a trauma history watched, segmented, and recalled videos of everyday activities. Viewers with higher PTSD symptom severity showed lower agreement on locations of event boundaries and recalled fewer fine-grained actions than did those with lower symptom severity. These results suggest that PTSD symptoms alter event segmentation, which may contribute to subsequent memory disturbances.

Semantic knowledge attenuates age-related differences in event segmentation and episodic memory.

While semantic and episodic memory may be distinct memory systems, their interdependence is substantial. For instance, decades of work have shown that semantic knowledge facilitates episodic memory. Here, we aim to clarify this interactive relationship by determining whether semantic knowledge facilitates the acquisition of new episodic memories, in part, by influencing an encoding mechanism, event segmentation. In the current study, we evaluated the extent to which semantic knowledge shapes how people segment ongoing activity and how such knowledge-related benefits in segmentation affect episodic memory performance. To investigate these effects, we combined data across three studies that had young and older adults segment and remember videos of everyday activities that were either familiar or unfamiliar to their age group. We found age-related differences in event-segmentation ability and memory performance, but only when older adults lacked semantic knowledge. Most importantly, when they had access to relevant semantic knowledge, older adults segmented and remembered information similar to young adults. Our findings indicate that older adults can use semantic knowledge to effectively encode and retrieve everyday information. These effects suggest that future interventions can leverage older adults' intact semantic knowledge to attenuate age-related deficits in event segmentation and episodic long-term memory.

Unexpected formation of oxygen-free products and nitrous acid from the ozonolysis of the neonicotinoid nitenpyram.

The neonicotinoid nitenpyram (NPM) is a multifunctional nitroenamine [(R1N)(R2N)C=CHNO2] pesticide. As a nitroalkene, it is structurally similar to other emerging contaminants such as the pharmaceuticals ranitidine and nizatidine. Because ozone is a common atmospheric oxidant, such compounds may be oxidized on contact with air to form new products that have different toxicity compared to the parent compounds. Here we show that oxidation of thin solid films of NPM by gas-phase ozone produces unexpected products, the majority of which do not contain oxygen, despite the highly oxidizing reactant. A further surprising finding is the formation of gas-phase nitrous acid (HONO), a species known to be a major photolytic source of the highly reactive hydroxyl radical in air. The results of application of a kinetic multilayer model show that reaction was not restricted to the surface layers but, at sufficiently high ozone concentrations, occurred throughout the film. The rate constant derived for the O3-NPM reaction is 1 × 10-18 cm3⋅s-1, and the diffusion coefficient of ozone in the thin film is 9 × 10-10 cm2⋅s-1 These findings highlight the unique chemistry of multifunctional nitroenamines and demonstrate that known chemical mechanisms for individual moieties in such compounds cannot be extrapolated from simple alkenes. This is critical for guiding assessments of the environmental fates and impacts of pesticides and pharmaceuticals, and for providing guidance in designing better future alternatives.

Dynamic interplay between PTSD symptoms and posttraumatic growth in older military veterans.

BACKGROUND: Posttraumatic growth (PTG) refers to positive psychological changes that may occur after experiencing a traumatic event. While cross-sectional studies have suggested that posttraumatic stress disorder (PTSD) is associated with greater PTG, few longitudinal studies have evaluated interrelationships between PTSD and PTG. Further, little is known about which specific symptom clusters of PTSD and coping mechanisms may drive PTG over time. METHODS: We evaluated interrelationships between PTSD symptoms and PTG using data from a 4-year, nationally representative, prospective cohort study of 2,006 older trauma-exposed U.S. veterans. RESULTS: Autoregressive cross-lagged panel regression analyses revealed that greater severity of PTSD symptoms was associated with greater PTG over time. Specifically, greater severity of the avoidance and anxious arousal (e.g., hypervigilance) symptoms at Wave 1 predicted greater PTG at Wave 2; and greater severity of avoidance and lower severity of dysphoric arousal (e.g., sleep disturbance) at Wave 2 predicted greater PTG at Wave 3. Engagement in active coping and religious coping were associated with greater subsequent PTG above and beyond autoregressive associations between PTSD and PTG. LIMITATIONS: The self-report nature of the assessments, discrete assessment periods assessed, and focus on older military veterans are study limitations. CONCLUSIONS: Greater severity of PTSD symptoms, particularly avoidance and hyperarousal symptoms, may contribute to and maintain PTG over time in older veterans. Interventions that promote deliberate, constructive attempts to manage chronic PTSD symptoms via active coping and religious coping may help veterans better manage PTSD symptoms and experience greater PTG in late-life.

Depression and Cognitive Dysfunction in Older U.S. Military Veterans: Moderating Effects of BDNF Val66Met Polymorphism and Physical Exercise.

OBJECTIVE: Depression is associated with increased risk for cognitive dysfunction, yet little is known about genetic and behavioral factors that may moderate this association. Using data from a nationally representative sample of older U.S. military veterans, we examined the direct and interactive effects of depression, brain-derived neurotropic factor (BDNF) Val66Met genotype, and physical exercise on cognitive functioning. METHODS: One thousand three hundred eighty-six older European-American U.S. military veterans (mean age = 63) completed a web-based survey and cognitive assessment. Analyses of covariance were conducted to evaluate the effects of depression, BDNF Met allele carrier status, and physical exercise on these measures. RESULTS: Depressed veterans scored worse than nondepressed veterans on subjective measures of cognitive functioning (Cohen d's = 0.34-0.57) and objective measures of visual learning (d = 0.39) and working memory (d = 0.28). Among depressed veterans, those who were Met allele carriers scored worse than Val/Val homozygotes on subjective cognitive measures (d's = 0.52-0.97) and an objective measure of visual learning (d = 0.36). Engagement in physical exercise moderated the association between depression and cognitive function, with depressed exercisers scoring better than depressed nonexercisers on a subjective measure of reasoning, and objective measures of processing speed, attention, and visual learning (d = 0.58-0.99): further, in depressed Met allele carriers, exercisers scored better than nonexercisers on subjective cognitive (d's = 0.80-1.92), and objective measures of visual learning (d = 0.8-1.31) and working memory (d = 0.67). CONCLUSION: Depression is associated with moderate decrements in cognitive functioning in older U.S. military veterans, and this association is moderated by BDNF Val66Met genotype and physical exercise. Prevention and treatment efforts designed to promote physical exercise may help preserve cognitive functioning in at-risk veterans.

Novel ionization reagent for the measurement of gas-phase ammonia and amines using a stand-alone atmospheric pressure gas chromatography (APGC) source.

RATIONALE: Contaminants present in ambient air or in sampling lines can interfere with the target analysis through overlapping peaks or causing a high background. This study presents a positive outcome from the unexpected presence of N-methyl-2-pyrrolidone, released from a PALL HEPA filter, in the analysis of atmospherically relevant gas-phase amines using chemical ionization mass spectrometry. METHODS: Gas-phase measurements were performed using a triple quadrupole mass spectrometer equipped with a modified atmospheric pressure gas chromatography (APGC) source which allows sampling of the headspace above pure amine standards. Gas-phase N-methyl-2-pyrrolidone (NMP) emitted from a PALL HEPA filter located in the inlet stream served as the ionizing agent. RESULTS: This study demonstrates that some alkylamines efficiently form a [NMP + amine+H]+ cluster with NMP upon chemical ionization at atmospheric pressure. The extent of cluster formation depends largely on the proton affinity of the amine compared with that of NMP. Aromatic amines (aniline, pyridine) and diamines (putrescine) were shown not to form cluster ions with NMP. CONCLUSIONS: The use of NMP as an ionizing agent with stand-alone APGC provided high sensitivity for ammonia and the smaller amines. The main advantages, in addition to sensitivity, are direct sampling into the APGC source and avoiding uptake on sampling lines which can be a significant problem with ammonia and amines.

Evidence for a kinetically controlled burying mechanism for growth of high viscosity secondary organic aerosol.

Secondary organic aerosol (SOA) particles are ubiquitous in air and understanding the mechanism by which they grow is critical for predicting their effects on visibility and climate. The uptake of three organic nitrates into semi-solid SOA particles formed by α-pinene ozonolysis either with or without an OH scavenger was investigated. Four types of experiments are presented here. In Series A, uptake of the selected organic nitrates (2-ethylhexyl nitrate (2EHN); ß-hydroxypropyl nitrate (HPN); ß-hydroxyhexyl nitrate (HHN)) into impacted SOA particles was interrogated by attenuated total reflectance (ATR)-FTIR. In this case, equilibrium was reached and partition coefficients (KSOA = [-ONO2]SOA/[-ONO2]air) were measured to be K2EHN = (3.2-11) × 104, KHPN = (4.4-5.4) × 105, and KHHN = (4.9-9.0) × 106. In Series B, SOA particles were exposed on-the-fly to gas phase organic nitrates for comparison to Series A, and uptake of organic nitrates was quantified by HR-ToF-AMS analysis, which yielded similar results. In Series C (AMS) and D (ATR-FTIR), each organic nitrate was incorporated into the SOA as the particles formed and grew. The incorporation of the RONO2 was much larger in Series C and D (during growth), exceeding equilibrium values determined in Series A and B (after growth). This suggests that enhanced uptake of organic nitrates during SOA formation and growth is due to a kinetically controlled "burying" mechanism, rather than equilibrium partitioning. This has important implications for understanding SOA formation and growth under conditions where the particles are semi-solid, which is central to accurately predicting properties for such SOA.

Quantum Yields and N2O Formation from Photolysis of Solid Films of Neonicotinoids.

Neonicotinoids (NN), first introduced in 1991, are found on environmental surfaces where they undergo photolytic degradation. Photolysis studies of thin films of NN were performed using two approaches: (1) transmission FTIR, in which solid films of NN and the gas-phase products were analyzed simultaneously, and (2) attenuated-total-reflectance FTIR combined with transmission FTIR, in which solid films of NN and the gas-phase products were probed in the same experiment but not at the same time. Photolysis quantum yields using broadband irradiation centered at 313 nm were (2.2 ± 0.9) × 10-3 for clothianidin (CLD), (3.9 ± 0.3) × 10-3 for thiamethoxam (TMX), and (3.3 ± 0.5) × 10-3 for dinotefuran (DNF), with all errors being ±1 s. At 254 nm, which was used to gain insight into the wavelength dependence, quantum yields were in the range of (0.8-20) × 10-3 for all NNs, including acetamiprid (ACM) and thiacloprid (TCD). Nitrous oxide (N2O), a potent greenhouse gas, was the only gas-phase product detected for the photolysis of nitroguanidines, with yields of ΔN2O/ΔNN > 0.5 in air at both 313 and 254 nm. The atmospheric lifetimes with respect to photolysis for CLD, TMX, and DNF, which absorb light in the actinic region, are estimated to be 15, 10, and 11 h, respectively, at a solar zenith angle of 35° and 12, 8, and 10 h at a solar zenith angle of 15°.

BDNF Val66Met polymorphism and posttraumatic stress symptoms in U.S. military veterans: Protective effect of physical exercise.

The Met allele of the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism is associated with reduced levels of BDNF release, heightened hypothalamic-pituitary-adrenal axis reactivity, and impaired fear extinction. As a result, Met allele carriers may be at risk for greater severity of posttraumatic stress disorder (PTSD) symptoms. In this study, we examined the relationship between the BDNF Val66Met polymorphism and PTSD symptoms in two nationally representative samples of European American U.S. military veterans (main sample, n = 1386; replication sample, n = 509). Results revealed that, relative to Val/Val homozygotes, Met allele carriers reported greater severity of lifetime and current PTSD symptoms, specifically re-experiencing symptoms. Met allele carriers with high trauma burden also reported greater severity of lifetime and past-month PTSD symptoms. Greater engagement in physical exercise moderated this gene-by-environment interaction. Specifically, among veterans with high lifetime trauma burden, Met allele carriers who exercised had significantly lower severity of PTSD symptoms compared to those who did not exercise. These findings suggest that interventions designed to bolster engagement in physical exercise may help mitigate PTSD symptoms in veterans who are Met allele carriers and highly exposed to trauma.

Uptake of water by an acid-base nanoparticle: theoretical and experimental studies of the methanesulfonic acid-methylamine system.

The effect of water on the growth of dry nano-size acid-base particles is not yet known. In this paper, we investigate the uptake of water by nano-size particles composed of methanesulfonic acid (MSA) and methylamine (MA) using a combination of quantum chemical calculations and laboratory experiments. Calculations were performed on the (MSA-MA)4 cluster as the dry nanoparticle model, which forms a pseudo-cubic structure, to which twelve water molecules were added successively. Theoretical results show that the hydrated clusters (MSA-MA)4-(H2O)n, n = 1 to 12 are thermodynamically stable. In ab initio dynamic simulations, no loss of water or significant changes of structure are seen for at least 10 picoseconds. In all the clusters studied, most of the water molecules lie on the face of the (MSA-MA)4 initial dry unit, and water is found to be incorporated inside the initial unit for n ranging from five to twelve. Sizes of hydrated clusters exceed significantly that of the dry cluster only for n ≥ 6. These theoretical results suggest that dry MSA-MA clusters cannot dissociate in small quantities of water. Calculations of hydrated cluster distributions at steady state show that the cluster compositions studied, with up to 12 water molecules, encompass all the hydrated clusters under the experimental conditions (RH ∼ 19%, 300 K). Experiments performed in a glass flow reactor showed no changes in size or number concentration when particles formed from MSA-MA were subsequently exposed to water vapor, in contrast to increases in both size and number when water was present during particle formation. Thus, the results seem to imply for both experiment and theory that growth in size of a particle due to uptake of water requires the previous presence of some level of hydration. These results illustrate the importance for atmospheric models of understanding on a molecular basis the mechanisms of particle formation in air.

Photochemistry of Solid Films of the Neonicotinoid Nitenpyram.

The environmental fates of nitenpyram (NPM), a widely used neonicotinoid insecticide, are not well-known. A thin solid film of NPM deposited on a germanium attenuated total reflectance (ATR) crystal was exposed to radiation from a low-pressure mercury lamp at 254 nm, or from broadband low pressure mercury photolysis lamps centered at 350 or 313 nm. The loss during photolysis was followed in time using FTIR. The photolysis quantum yields (ϕ), defined as the number of NPM molecules lost per photon absorbed, were determined to be (9.4 ± 1.5) × 10-4 at 350 nm, (1.0 ± 0.3) × 10-3 at 313 nm, and (1.2 ± 0.4) × 10-2 at 254 nm (±2σ). Imines, one with a carbonyl group, were detected as surface-bound products and gaseous N2O was generated in low (11%) yield. The UV-vis absorption spectra of NPM in water was different from that in acetonitrile, dichloromethane, and methanol, or in a thin solid film. The photolytic lifetime of solid NPM at a solar zenith angle at 35° is calculated to be 36 min, while that for NPM in water is 269 min, assuming that the quantum yield is the same as in the solid. Thus, there may be a significant sensitivity to the medium for photolytic degradation and the lifetime of NPM in the environment.

Risk Factors for Suicidal Behavior Depend on Age for Veterans in the Pacific Islands.

We examined whether risk factors for suicidal behavior depend on age among military veterans in the Pacific Islands (N = 29,595). For veterans under 54 years old, having a diagnosis of posttraumatic stress disorder, borderline personality disorder, a drug use disorder, and having a service-related disability predicted suicidal behavior. For veterans 54 years old or older, having a mood disorder predicted suicidal behavior. Having a history of suicidal behavior and a high number of VA health care visits were associated with suicidal behavior for both age groups. Our findings suggest that the predictive value of certain risk factors in veterans in the Pacific Islands may depend on age.

Nanoparticles grown from methanesulfonic acid and methylamine: microscopic structures and formation mechanism.

Mechanisms of particle formation and growth in the atmosphere are of great interest due to their impacts on climate, health and visibility. However, the microscopic structures and related properties of the smallest nanoparticles are not known. In this paper we pursue computationally a microscopic description for the formation and growth of methanesulfonic acid (MSA) and methylamine (MA) particles under dry conditions. Energetic and dynamics simulations were used to assess the stabilities of proposed model structures for these particles. Density functional theory (DFT) and semi-empirical (PM3) calculations suggest that (MSA-MA)4 is a major intermediate in the growth process, with the dissociation energies, enthalpies and free energies indicating considerable stability for this cluster. Dynamics simulations show that this species is stable for at least 100 ps at temperatures up to 500 K, well above atmospheric temperatures. In order to reach experimentally detectable sizes (>1.4 nm), continuing growth is suggested to occur via clustering of (MSA-MA)4. The dimer (MSA-MA)4(MSA-MA)4 may be one of the smaller experimentally measured particles. Step by step addition of MSA to (MSA-MA)4, is also a likely potential growth mechanism when MSA is excess. In addition, an MSA-MA crystal is predicted to exist. These studies demonstrate that computations of particle structure and dynamics in the nano-size range can be useful for molecular level understanding of processes that grow clusters into detectable particles.