Progress 05/01/20 to 04/30/24
Outputs
Target Audience:The project will target scientific researchers, teachers, and extention specialists who benefit from the fundamental knowledge gained by the study. However, the Project will provide critical insight into the molecular-level associations of organic matter in geosolids that are important for soil health, and therefore will ultimately benefit stakeholders in the agricultural arena vis a vis crop protection, regulators and offcials who deal with the risks of environmental pollution, and the general public who suffer the consequences of environmental pollution. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?This project has provided valuable professional experience for the postdoctoral scientist, Zhengyang Wang, who plans an academic career. This project has also provided an opportunity for Professor Hirotatsu Murano, a soil scientist from Laboratory of Environmental Soil Science, Faculty of Agriculture, Meijo University in Aichi, Japan, to expand his expertise and interact with us. He visited us for 1 year during a previous reporting period. However, Prof. Murano and his undergraduate students, Mayu Nagata, Kenichi Amano, and Masahiro Maebayashi, have continued to generate crucial data from his laboratory at Meijo University in support of the project. How have the results been disseminated to communities of interest?The results of this project have been reported at numerous scientific conferences. In addition to the ones reported in the annual Progress Reports, within the last reporting periodthey include the following: 1. J. Pignatello, "Involvement of very strong hydrogen bonds in soil organic matter aggregation, adhesion, and interaction with pollutants,"FY2024 A1401 (Soil Health) NIFA Project Directors Meeting, Kansas City MO; April 9-11, 2024. 2. Mayu NAGATA, Zhengyang WANG, Kenichi AMANO, Masahiro MAEBAYASHI, Hirotatsu MURANO, Joseph PIGNATELLO, "Effect of Strong Charge-Assisted Hydrogen Bonds in interaction of Dissolved Organic Matter.Japan Society of Soil and Plant Nutrition,Fukuoka, Japan;September 3-5, 2024 (in Japanese). What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Terrestrial dissolved organic matter (DOM) plays critical roles in many biotic and abiotic environmental reactions as well as in water treatment. Its structure is therefore of great interest. We examined dissolved Suwannee River Humic Acid (SRHA) to probe the potential participation of exceptionally strong, negative charge-assisted hydrogen bonds, (−)CAHB, in DOM cohesion and interaction with small weak acids using high performance size exclusion chromatography (HPSEC), transmission electron microscopy, zeta-pH curves, and pH drift experiments. The results support a previously proposed two-tier state of aggregation, in which tightly-knit primary particles (≤ ~10kDa) form larger secondary aggregates (up to micrometer in size). Evidence for (−)CAHB is gained through zeta potential changes, induced HPSEC shifts,and pH drift experiments. The primary particles interact with (−)CAHB-capable solutes (simple carboxylic acids and phosphate) but not (−)CAHB-incapable solutes. We identified disruption of intra-segmental and inter-molecular (−)CAHB leading to swelling and disaggregation, as well as formation of nouveau (−)CAHB with free groups on SRHA. The effects were solute-concentration dependent and greater at pH 5 than pH 6, consistent with CAHB theory. Phosphate induced the greatest shifts in the HPSEC molecular size distribution curves, apparently as the H2PO4− ion.The shifts were unaffected by prior stripping of innate polyvalent metals. Benzoate and 4-hydroxybenzoate are more effective at promoting disaggregation of primary particles than the smaller formate and acetate, suggesting that hydrophobic effects and van der Waals interactions with SRHA segments provide a secondary driving force for separation of SRHA molecules. Properties attributable to HA by HPSEC behavior apply only to the primary particles, as they are the only ones that pass through the column. Researchers using HPSEC should check for elution recovery and normalize for it to avert misinterpretation of MWD curves. While the results of this study taken as a whole fully support the involvement of (−)CAHB in particle cohesion, the concentration independence of the shape of the HPSEC MWD curves representing the primary particles is ambiguous with respect to the macromolecular versus supramolecular concepts of DOM. Nevertheless, the supramolecular model is supported if it is assumed that primary particle molecules are held together by the great strength of the (−)CAHB. Clearly, however, the secondary particles must be aggregates. We conclude that the (−)CAHB contributes to the cohesion of DOM, affecting its size and charge, and also provides a mechanism by which weak acid pollutants, nutrients, and natural compounds can interact with DOM. Such interactions have implications for the behavior of DOM in the environment, the fate and transport of anthropogenic pollutants, and the roles DOM play in water treatment technologies.The CAHB can play potentially important roles in the behavior of natural organic matter. It can affect soil/sediment organic matter water solubility. It may affect the binding of DOM to geosorbents which, in turn, has implications for the mobility and bioavailability of DOM in the soil column. The CAHB may affect DOM binding to membranes and carbonaceous sorbents used in water purification which can affect their performance. The proton in a (−)CAHB complex is generally less dissociable than the proton in the corresponding free acids of the pair, implying a role for (−)CAHB in the property of DOM as a natural buffer. Many agrochemicals, pharmaceuticals, personal care products, and other anthropogenic compounds have weakly acidic functional groups with pKa values close to the pKa of acidic groups on DOM, and therefore--like the carboxylic acids tested here--are capable of forming CAHBs with DOM at environmentally relevant pH. In the environment, CAHB formation is expected to be affected by the concentration of functional groups with closely similar pKa, ionic strength, pH, and the concentrations of cations. Future work should focus on quantifying the roles CAHB may play in processes relevant to DOM environmental behavior and water treatment. Lastly, our results are restricted to SWHA. As a well-studied reference material isolated from natural waters in high yield and with no harsh chemical exposure, SRHA certainly can be considered representative of some DOM. Nevertheless, samples of DOM from other sources must be tested to evaluate the generality of our conclusions.
Publications
- Type:
Journal Articles
Status:
Awaiting Publication
Year Published:
2024
Citation:
Zhengyang Wang, Mayu Nagata, Hirotatsu Murano*, and Joseph J. Pignatello*, Participation of Strong Charge-Assisted Hydrogen Bonds in Interactions of Dissolved Organic Matter Represented by Suwannee River Humic Acid, Water Research.
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Progress 05/01/22 to 04/30/23
Outputs
Target Audience:The project will target scientific researchers, teachers, and extention specialists who benefit from the fundamental knowledge gained by the study. However, the Project will provide critical insight into the molecular-level associations of organic matter in geosolids that are important for soil health, and therefore will ultimately benefit stakeholders in the agricultural arena vis a vis crop protection, regulators and offcials who deal with the risks of environmental pollution, and the general public who suffer the consequences of environmental pollution. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?This project has provided valuable professional experience for the postdoctoral scientist, Zhengyang Wang, who plans an academic career. This project has also provided an opportunity for Professor Hirotatsu Murano, a soil scientist from Laboratory of Environmental Soil Science, Faculty of Agriculture, Meijo University in Aichi, Japan, to expand his expertise and interact with us. He visited us for 1 yearduring the previous reporting period. However, Prof. Murano and his undergraduate student, Mayu Nagata,have continued to generate crucial data from his laboratory at Meijo University in support of the project. How have the results been disseminated to communities of interest?"Environmental chemistry of ionizable organic contaminants: formation of Charge-Assisted Hydrogen Bonds between ions of similar proton affinity in sorption and aggregation interactions", J. Pignatello; Environmental Chemistry and Nanotechnology:A Tribute to Joel Pedersen; American Chemical Society National Meeting, San Francisco, CA, August 2023. What do you plan to do during the next reporting period to accomplish the goals?The experiments are largely completed. We requested, and received, a one-year, no-cost extention to complete data workup and write and submit a full paper to the journal Water Research.
Impacts
What was accomplished under these goals?
Our objectives in the reporting period were two-fold: to detect whether CAHB plays an important role in intra- and intermolecular interactions of dissolved organic matter (DOM), using Suwannee River Humic Acid (SRHA) as a reference material, and whether such interactions are affected by addition of small solutes capable of forming CAHB. To further this goal we carried out pH drift experiments to test the hypothesis that weak acids (BH =acetic, formic, or benzoic) can form nouveau (-)CAHB with SRHA with release of hydroxide into solution:. dom-X− + B− + H2O --> dom-X−...H+...−B+ OH− (1) where X is an acidic group on the DOM, for example carboxyl. Previous of our studies with activated carbon, biochar and carbon nanotubes showed that acidic functional groups could form a (-)CAHB with added BH. In addition, we showed that the hydroxide released is attenuated by buffering by the substrate. In the present study, the substrate isSRHA, which consumes hydroxide via eq 2, and BH is the undissociated form of the added weak acid, which consumes hydroxide via eq 3. dom-XH + OH- -->dom-X- + H2O (2) BH + OH- --> B- + H2O(3) Thus, we hypothesize that formation of nouveau (−)CAHB according to eq 1would lead to an increase in pH. Solutions of SRHA (80 mg-C L-1) adjusted to 10 or 100 mM IS and a stable pH near 4.5 or 6.0 were then mixed with a solution of the desired chemical additive pre-adjusted to the same IS and stable pH. The vials were shaken in the dark at 25 °C for up to 9 days. The controls without added BH showed little or no pH drift over the course of the experiment at either nominal pH, indicating proton exchange equilibrium of SRHA itself. However, at nominal pH 4.5, the pH of the control (4.31) rose to 7.01 by mixing with formate, 4.81 with acetate, and 4.60 with benzoate after 216 h. At nominal initial pH 6, the pH of the control (5.76) rose to 7.58 with formate and 6.43 with acetate.The pH increases can be attributed to nouveau (−)CAHB formation in which a proton from water is required (eq 1). They take a few days to fully manifest due to slow rearrangement of the SRHA structure needed to achieve orientation of groups. To correct for buffering, a corrected hydroxide released was computed for each time point that showed a significant observed pH change. The corrected hydroxide released is the sum of the observed hydroxide released, hydroxide consumed by SRHA (eq 2, computed from a separate titration curve), and hydroxide consumed by undissociated BH(eq 3, computed from its pKa) upon transitioning from control pH to observed pH. It was assumed, to a first approximation, that weak acid and SRHA act as independent buffers. The corrected hydroxide released can then be converted to a corrected pH at each time point (pHcorr, t). We found that the pHcorr,tvalues (9.4-10.6) are much greater than the observed values. The fraction of weak acid that engaged in CAHB with consumption of a proton is just the ratio of corrected hydroxide released to total BH added. Accordingly, the computed percent weak acid engaged in CAHB accompanied by proton release is as follows: at nominal pH 4.5: 47-61% of formate, 39% of acetate, and 20% of benzoate; at nominal pH 6: 9-16% of formate and 9-13% of acetate. CAHB is more favorable at initial nominal pH 4.5 than pH 6because pH 4.5 is closer to the nominal pKa1 of SRHA (4.47computed from the titration curve), fullyconsistent with CAHB theory. In summary, the results are consistent with the hypothesis that weak acid solutes can form a (-)CAHB with DOM. Many pesticides, pharmaceauticals, and other chemicals used in consumer products contain weak acid functional groups, expecially carboxyl.The results have significant ramifications for the behavior of agricultural and other chemicals in soil and natural waters.
Publications
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Progress 05/01/21 to 04/30/22
Outputs
Target Audience:The project will target scientific researchers, teachers, and extention specialists who benefit from the fundamental knowledge gained by the study. However, the Project will provide critical insight into the molecular-level associations of organic matter in geosolids thatare important for soil health, and therefore will ultimatelybenefit stakeholders in the agricultural arena vis a vis cropprotection, regulators and offcials who deal with the risks of environmental pollution, and the general public who suffer the consequences of environmental pollution. Changes/Problems:We were severely hindered in the performance of this research by COVID19. The Murano laboratory was completely shut down for most of the year and the Pignatello laboratory was partially shut down. The COVID19 pandemic caused a lengthy delay in obtaining a replacement size exclusion chromatography column for the project. What opportunities for training and professional development has the project provided?This project has provided valuable professional experience for the postdoctoral scientist, Zhengyang Wang, who plans an academic career. This project has also provided an opportunity for Professor Hirotatsu Murano, a soil scientist from Laboratory of Environmental Soil Science,Faculty of Agriculture, Meijo University in Aichi, Japan, to expand his expertise and interact with us during a 1-year visit. This visit ended in April 2020, but Prof. Murano has continued to generate data from his laboratory at Meijo University in support of the project. This project has also provided valuable experience for a seasonal researcher, Tyler Swanson, who was a Masters student at Central Connecticut State University in Berlin. Heworked a combination of volunteer and paid time totalling about 4 months in 2021. How have the results been disseminated to communities of interest?Zhengyang Wang, Hirotatsu Murano, and Joseph J. Pignatello, Dynamic Aggregation of Humic Acid in the Absence and Presence of Added Low-molecular-weight Acids, ZSSSA National meeting, Symposium in Honor of Donald Sparks, Salt Lake City, November 2021. A manuscript is in preparation. What do you plan to do during the next reporting period to accomplish the goals?Work continues on characterizing a) the molecular weight distrubution of dissolved humic and fulvic acids (DOM) in the presence and absence of CAHB-capable weak acids; b) the zeta potential of DOM in thepresence and absence of CAHB-capable weak acids; and c) the leakage of DOM through dialysis membranes as a function ofCAHB-capable weak acid concentration. Experiments will be initiated on the sorption ofCAHB-capable weak acid contaminants to DOM using a dialysis cell apparatus to separate DOM from the bulk solution.
Impacts
What was accomplished under these goals?
Dissolved organic matter (DOM) is important in a myriad of biotic and abiotic environmental processes. The current 'supramolecular' paradigm of DOM holds that entities are aggregates of smaller molecules held together by weak forces. However, the forces holding DOM supramolecular aggregates are not well understood. We conducted experiments on aqueous solutions of Suwanee River humic and fulvic acids (HA and FA) to probe these forces. DOM aggregates appear to be substantial in size, failing to leak over many days through membranes of nominal molecular-weight cutoff up to 3.5 kDa (FA) or 8 kDa (HA). Moreover, molecular weight distribution or aggregate size is insensitive to DOC concentration (10x range), pH (6-7), and ionic strength (0.1-1.6 M), suggesting that intra-aggregate forces are substantial. We provide evidence for the intra-aggregate formation of exceptionally strong, charge-assisted hydrogen bonds (CAHB) between acidic groups on DOM (e.g., -CO2H groups), a portion of which help stabilize the aggregate. Furthermore, we show that DOM groups can form CAHBs with added weak acids have similar pKa and thus capable of forming CAHB (e.g., formate, acetate, phosphate). Some of the CAHB compete for intra-aggregate CAHB links and therefore promote DOM disaggregation. Evidence for intra-aggregate CAHB formation includes the following: i) We observe a shift in the UV size exclusion chromatogram of HA to higher retention time (i.e., lower molecular weight distribution) after adding phosphate or acetate at controlled pH of 5 or 6. ii) A 'hump' appears in the zeta potential-pH curve of DOM centered at pH 5-6, consistent with loss of negative charge through intra-aggregate CAHB formation: i.e., OM-CO2- + OM-CO2- + H+--> OM-CO2-...H+...-O2C-OM). This hump persists in the presence of non-CAHB forming molecules such as DMSO or methanol, but disappears when a CAHB-capable ion, acetate or phosphate, is present. iii) Leakage of HA or FA through a dialysis membrane is accelerated upon addition of phosphoric or acetic acids, consistent with disruption of aggregate cohesion and formation of smaller molecules. iv) Starting at pH 6, an increase in pH is observed after addition of weak acid anions XO- consistent with CAHB formation of free carboxyl groups with the added anion: i.e., OM-CO2- + XO- + H2O --> OM-CO2-...H+...-OX + OH-.
Publications
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Progress 05/01/20 to 04/30/21
Outputs
Target Audience:The knowledge gained from this study will provide critical insight into the molecular-level behaviour of dissolved organic matter in soil that are important for soil health, and may lead to strategies that reduce crop uptake of chemical contaminants. The project targets researchers, teachers, and extention specialists who benefit from the fundamental knowledge gained. I will ultimately benefit stakeholders in the agricultural arena interested in crop pretection, regulators and officials who deal with risks of pollution, and the general public who suffer the consequences of environmental pollution. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?This project has provided valuable professional experience for the postdoctoral scientist, Zhengyang Wang, who plans an academic career. This project has also provided an opportunityfor Professor HirotatsuMurano, a soil scientist from Laboratory of Environmental Soil Science, Faculty of Agriculture, Meijo University in Aichi, Japan, to expand his expertise and interact with us during a 1-year visit. How have the results been disseminated to communities of interest?We will be presenting the results at the annual meeting of the Soil Science Society of America in Salt Lake City in November, 2021. What do you plan to do during the next reporting period to accomplish the goals?Research planned in the coming year is as follows: Using the SEC technique, test other weak acids for their ability to disaggregate dissolved organic matter, including acetic , benzoic, and phosphoric acids. Using the SEC technique, test other dissolved organic matter samples. Determine the partitioning of formic acid into dissolved HA using a dialysis membrane separation technique. This technique involves emplacement of dissolved HA inside a dialysis tube in equilibrium with a solution of 14C-labeled formate and measuring the partitioning of formate between the internal and external fluids. Determine the partitioning of certain weak acid pollutant compounds into dissolved HA using the same dialysis membrane separation technique.
Impacts
What was accomplished under these goals?
Progress was made by the PI's group on Objective 1,To detect CAHB interactions of natural organic matter in solution. Size exclusion chromatography (SEC) was applied to solutions of a standard reference Suwanee River humic acid (HA) from the International Humic Substances Society at pH 6 and ionic strength of 0.1 M (NaCl) in a mobile phase of identical composition using UV detection. Chromatograms were calibrated against that of acetone and a set of polystyrene sulfonate standards of known molecular size. The UV chromatograms showed that with dilution of HA concentration the number-average molecular weight decreasedand the peak width at half height increased. Thissupports recent proposals that dissolved OM in aqueous solution exists as aggregates in solution that tend to disperse as the solution is diluted. However, we also found that HA does not begin toleak through the pores of a dialysis membrane until the nominal pore size reaches a certain value of about 5K Daltons. Addition of 10 mM formate (NaHCO2) to solutions ofHA at a given concentration and at constant pH and ionic strength leads to a decrease in the tailing of the UV peak at the high molecular weight (short retention time) end of the chromatogram, together with an increase in absorbance at the low molecular weight end of the chromatogram. Addition of 10 mM methanol had no effect on peak shape. These results point to a specific role for formate, and are consistent with a mechanism by which HCO2- disperses HA aggregates via formation of (-)CAHBs with HA groups in competition with intra-aggregate (-)CAHBs ; i.e., HCO2- + {HA-CO2...H...O2C-HA}---> {HCO2...H...O2C-HA}- + HA-CO2-. The results provide tentative evidence for the importance of (-)CAHBs in aggregation of OM in solution.
Publications
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