Large Molecular Weight Fraction Research Articles

Nanoscale Sequential Reactor Design Achieves Effective Removal of Disinfection Byproduct Precursors in Catalytic Ozonation.

Transforming dissolved organic matter (DOM) is a crucial approach to alleviating the formation of disinfection byproducts (DBPs) in water treatment. Although catalytic ozonation effectively transforms DOM, increases in DBP formation potential are often observed due to the accumulation of aldehydes, ketones, and nitro compound intermediates during DOM transformation. In this study, we propose a novel strategy for the sequential oxidation of DOM, effectively reducing the levels of accumulation of these intermediates. This is achieved through the development of a catalyst with a tailored surface and nanoconfined active sites for catalytic ozonation. The catalyst features a unique confinement structure, wherein Mn-N4 moieties are uniformly anchored on the catalyst surface and within nanopores (5-20 Å). This design enables the degradation of the large molecular weight fraction of DOM on the catalyst surface, while the transformed smaller molecular weight fraction enters the nanopores and undergoes rapid degradation due to the confinement effect. The generation of *Oad as the dominant reactive species is essential for effectively reducing these ozone refractory intermediates. This resulted in over 70% removal of carbonaceous and nitrogenous DBP precursors as well as brominated DBP precursors. This study highlights the importance of the nanoscale sequential reactor design and provides new insights into eliminating DBP precursors by the catalytic ozonation process.

Insights into the transformation of dissolved organic matter and carbon preservation on a MnO2 surface: Effect of molecular weight of dissolved organic matter

Dissolved Organic Matter (DOM) is easily adsorbed and transformed by soil minerals and is an important redox-active component of soil and sediment. However, the effects of the molecular weight of DOM on the interface between MnO2 and DOM remain unclear. Herein, fulvic acid (FA) from peat was size-fractionated into four molecular weight fractions (FA>10kDa, FA5–10kDa, FA3–5kDa, and FA<3kDa) and then reacted with δ-MnO2 in this study. The affinity of FA for MnO2 varied significantly with different molecular weights, and large molecular weight FA was more easily adsorbed by MnO2. After 30 h of reaction, the highest mineralization rate was for FA>10kDa (42.39 %), followed by FA5–10kDa (28.65 %), FA3–5kDa (25.58 %), and FA<3kDa (20.37 %), consistent with the results of adsorption. The stronger reducing ability of the large molecular weight fraction of FA to MnO2 was mainly attributed to hydrophobic functional groups, promoting adsorption by MnO2 and the exposure of more active sites. The main active species involved in the mineralization of FA were •OH and Mn4+ through the quenching experiment. Our findings confirm that the large molecular weight fractions of FA play a crucial part in the adsorption and redox reactions of MnO2. These results may help evaluate the performance of different molecular characteristics of FA in the biogeochemical cycles of MnO2 in the soil environment.

Insight into the evolution characteristics on molecular weight of compost dissolved organic matters using high-performance size exclusion chromatography combined with a two-dimensional correlation analysis.

The information on molecular weight (MW) characteristics of DOM and relevant evolution behaviors during composting are limited. In this study, DOM extracted from co-composting of chicken manure and rice husks were comprehensively analyzed by using high-performance size exclusion chromatography (HPSEC) combined with a two-dimensional correlation spectroscopy (2D COS) to explore the evolution characteristics of MW of compost DOM. The HPSEC detected at UV of 254nm and at fluorescence (FL) Ex/Em wavelengths (315/410, 270/455nm) all showed a gradual increase in both weight-average and number-average MW for DOM, suggesting that the large MW fractions were continuously generated and polymerized during composting. The 2D COS applied on HPSEC-UV and -FL further identified the key active MW chromophoric (i.e., 0.5, 7.2. 9.5, 26.3, 30.7, and 83.9kDa) and fluorophoric (i.e., 0.55 and 3.5kDa) molecules that mainly participated in the transformation processes of compost DOM. Moreover, these active MW species were preferentially formed by the order of small to large molecules. A hetero-2D COS analysis disclosed the change sequence in the order of 0.5 and 7.2kDa chromophores → 3.5kDa fluorophores, and the 0.55 and 3.5kDa fluorophores → 26.3 and 83.9kDa chromophores.

Soil phosphomonoesters in large molecular weight material comprise multiple components

AbstractThe majority of soil organic P is typically that of “unresolved” phosphomonoesters, which are associated with organic P (Po) in large molecular weight (MW) fractions. However, the composition of this pool of Po remains unclear and could contain more than one component. Our aim was to identify the number and nature of components in soil extracts of different MW using solution 31P nuclear magnetic resonance (NMR) spectroscopy and spectral deconvolution fitting. Three surface soils were collected from native sites, which were extracted for Po using 0.25 M NaOH + 0.05 M Na2–EDTA (unfractionated), followed by size separation using ultrafiltration, resulting in four MW fractions (&gt;10 kDa, &lt;10 kDa, &lt;10 kDa and &gt;3 kDa, and &lt;3 kDa). The NMR analyses revealed a diversity of Po species in all MW fractions across the three soils. In particular, the phosphomonoester region of the &gt;10‐kDa fraction comprised up to 10 components of varying linewidth (0.5–18.6 Hz) and a broad signal (228 Hz). This broad signal was also present in the &lt;3‐kDa fraction, albeit at a lower concentration (average was 29% of that in the unfractionated extracts). Furthermore, solution 31P NMR spectra on the &lt;3‐kDa fraction revealed a diversity of sharp signals (up to 28) in the phosphomonoester region. Overall, our findings show that soil phosphomonoesters in large MW fractions comprise multiple components of varying linewidth.

Fish muscle hydrolysate obtained using largemouth bass Micropterus salmoides digestive enzymes improves largemouth bass performance in its larval stages.

The present study utilized digestives tracts from adult largemouth bass (LMB) to hydrolyze Bighead carp muscle and obtain an optimal profile of muscle protein hydrolysates that would be easily assimilated within the primitive digestive tract of larval LMB. Specifically, muscle protein source was digested for the larva using the fully developed digestive system of the same species. The objectives of this study were: 1) to develop an optimal in vitro methodology for carp muscle hydrolysis using LMB endogenous digestive enzymes, and 2) to evaluate the effect of dietary inclusion of the carp muscle protein hydrolysate on LMB growth, survival, occurrence of skeletal deformities, and whole-body free amino acid composition. The study found that the in vitro hydrolysis method using carp intact muscle and LMB digestive tracts incubated at both acid and alkaline pH (to mimic digestive process of LMB) yielded a wide range of low molecular weight fractions (peptides), as opposed to the non-hydrolyzed muscle protein or muscle treated only with acid pH or alkaline pH without enzymes from LMB digestive tracts, which were comprised of large molecular weight fractions (polypeptides above 150 kDa). Overall, the dietary inclusion of the carp muscle hydrolysate improved growth performance of larval LMB in terms of final average weight, weight gain, DGC, SGR, and body length after 21 days of feeding compared to fish that received the diet based on non-hydrolyzed carp muscle. The study also found that hydrolysate-based feed significantly reduced skeletal deformities. The positive growth performance presented by fish in the hydrolysate-fed group possibly resulted from matching the specific requirements of the larvae with respect to their digestive organ development, levels of digestive enzymes present in the gut, and nutritional requirements.

Analysis of asphaltenes and maltenes before and after long-term aging of bitumen

Asphaltenes and maltenes of bitumen before and after aging are investigated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (1H NMR), time of flight - secondary ion mass spectrometry (TOF-SIMS), and gel permeation chromatography (GPC). It has been shown that bitumen differs in terms of wax. After fractionation, more wax is found in the maltenes compared to the bitumen, and this is even more evident when bitumen is aged. For one bitumen, asphaltenes from the virgin binder do not contain carbonyls, which all fall into the maltenes. After bitumen aging, a large part of the carbonyl and sulfoxide signals is shifted to the asphaltenes. Differences in aromaticity are also evidenced as asphaltenes > bitumen > maltenes. TOF-SIMS shows that maltenes are close to the bitumen, but asphaltenes are more different. Also, maltenes are relatively unaffected by aging while larger differences are found in the asphaltenes between the virgin and aged binders. By GPC, a large molecular weight fraction of bitumen is shown as main part of the asphaltenes. However, asphaltenes also contain low molecular weight molecules that overlap with maltenes. Upon bitumen aging, some low molecular weight compounds may become part of asphaltenes, making the average molecular weight of the asphaltenes lower.

Gamma-irradiation-induced molecular-weight distribution and complexation affinity of humic acid with Cs+, Sr2+, and Eu3+

Solutions of humic acid (HA) were irradiated with 0, 1, 5, 10, 50, and 100 kGy of gamma irradiation using a 60Co source. The non-irradiated and irradiated HA molecules were fractionated by ultrafiltration into four categories: > 100, 50–100, 10–50, and < 10 kDa. Total organic carbon measurements and potentiometric titration analysis suggested that (1) some gamma-irradiated HA molecules were degraded into smaller molecules and (2) radiolytic degradation caused phenolic –OH became the predominant functional group in the small molecular-weight fractions of HA. The effect of absorbed dose of gamma rays on the distributions of Cs+, Sr2+, and Eu3+ ions in the molecular-weight fractions of the metal–HA systems was examined to discuss the complexation affinity. The metal ions were distributed in the smaller molecular-weight fractions at different doses, which corresponded to the degradation of HA molecules. For a predetermined absorbed dose, Cs+ ions did not change the molecular-weight distribution of the total organic carbon content of the degraded HA molecules. Conversely, the Sr2+ and Eu3+ ions redistributed organic carbon toward the larger molecular-weight fractions.

Wheat gluten stabilized emulsions: Influence of homogenization process, pH, and ethanol concentration on droplet breakup and stabilization

Wheat gluten's use as an emulsifier in vegetarian products is limited by insufficient understanding of its emulsifying properties. We prepared d-limonene based oil-in-water-emulsions with varying formulation and process parameters to elucidate its stabilizing mechanism.Gluten's emulsifying properties depend on the total gluten concentration in solution, which is influenced by pH. Low solubility can be compensated by dispersing a larger amount of gluten into the solution.Ethanol does not influence gluten solubility but enhances droplet breakup by reducing the interfacial tension between oil and aqueous phase. Consequently, in high-pressure homogenized emulsions, droplet sizes increased because gluten's adsorption kinetics were too slow to stabilize the amount of newly created interface resulting in recoalescence. Gluten hydrolyzation reduced the preferentially adsorbing large molecular weight fractions resulting in decreased steric stabilization.These findings indicate that the individual protein fractions might require targeted modifications to improve their solubility and adsorption kinetics.

Km23-1/DYNLRB1 regulation of MEK/ERK signaling and R-Ras in invasive human colorectal cancer cells.

We previously found that km23-1/DYNLRB1 is required for transforming growth factor-β (TGFβ) production through Ras/ERK pathways in TGFβ-sensitive epithelial cells and in human colorectal cancer (CRC) cells. Here we demonstrate that km23-1/DYNLRB1 is required for mitogen-activated protein kinase kinase (MEK) activation in human CRC cells, detected by km23-1/DYNLRB1-siRNA inhibition of phospho-(p)-MEK immunostaining in RKO cells. Furthermore, we show that CRISPR-Cas9 knock-out (KO) of km23-1/DYNLRB1 reduced cell migration in two additional CRC models, HCT116 and DLD-1. Of interest, in contrast to our previous work showing that dynein motor activity was required for TGFβ-mediated nuclear translocation of Smad2, in the current report, we demonstrate for the first time that disruption of dynein motor activity did not reduce TGFβ-mediated activation of MEK1/2 or c-Jun N-terminal kinase (JNK). Moreover, size exclusion chromatography of RKO cell lysates revealed that B-Raf, extracellular signal-regulated kinase (ERK), and p-ERK were not present in the large molecular weight fractions containing dynein holocomplex components. Furthermore, sucrose gradient fractionation of cell lysates from both HCT116 and CBS CRC cells demonstrated that km23-1/DYNLRB1 co-sedimented with Ras, p-ERK, and ERK in fractions that did not contain components of holo-dynein. Thus, km23-1/DYNLRB1 may be associated with activated Ras/ERK signaling complexes in cell compartments that do not contain the dynein holoprotein complex, suggesting dynein-independent km23-1/DYNLRB1 functions in Ras/ERK signaling. Finally, of the Ras isoforms, R-Ras is most often associated with cell migration, adhesion, and protrusive activity. Here, we show that a significant fraction of km23-1/DYNLRB1 and RRas wase co-localized at the protruding edges of migrating HCT116 cells, suggesting an important role for the km23-1/DYNLRB1-R-Ras complex in CRC invasion.

Adsorption of Dissolved Organic Matter with Different Relative Molecular Masses on Inorganic Minerals and Its Influence on Carbamazepine Adsorption Behavior

In this work, sorption experiments were conducted to understand the adsorption characteristics of dissolved organic matter (DOM) of different relative molecular masses on minerals and the effects of their interaction with PPCPs on the adsorption process. This study chose carbamazepine (CBZ) as the target pollutant, quartz sand as the inorganic mineral, and commercial humic acid (HA) as the DOM. We studied the structural characteristics of HA with different relative molecular masses and the impact of their interaction with CBZ on their adsorption based on dialysis experiments and infrared spectroscopy. It was found that large molecular weight fractions of HA, which contain more hydroxyl, aromatic hydrocarbons, and aliphatic hydrocarbons, were mainly hydrophobic substances, while the smaller fractions, containing more alcohols and carboxyl groups, were mainly hydrophilic substances. The combination of HA and CBZ had two major mechanisms, the combination of amino groups of CBZ and polar functional groups in small molecular weight fractions of HA and hydrophobic interactions between hydrophobic groups and aliphatic or/aromatic compounds in large molecular weight HA. The interaction between CBZ and HA resulted in obvious differences in the adsorption of HA or CBZ. When CBZ does not exist, hydrophobic combinations occurred between HA through the hydrophobic components and quartz sand, which also experienced the exchange coordination reaction with the hydroxyl or carboxyl group of HA. In addition, HA adsorbed the aliphatic and hydrophobic macromolecular components. Quartz sand was used to adsorb the large hydrophobic molecules. When CBZ existed, it adsorbed the small molecular weight fractions of HA. The maximum HA adsorption capacity of quartz sand decreased. CBZ could be adsorbed on quartz sand by hydrophobic interaction, van Edward forces, and polarity interactions in the absence of HA. When adding HA, the adsorption increment of carbamazepine on quartz sand was due to the co-adsorption or accumulation of HA and CBZ after their combination.

Formation of disinfection by-products in remineralized desalinated seawater with bacterial materials as precursor

As the essential target of disinfection, bacterial materials should also be considered as one type of disinfection by-products precursors (DBPs). This study investigated the disinfection by-products formation potential (DBPFP) of bacterial materials during chlorination and chloramination. The bacterial materials were harvested from mature biofilm developed in remineralized desalinated seawater with different carbon sources. It was observed that calcium and magnesium which were added to desalinated seawater for remineralization could enhance DBPFP of bacterial materials, with magnesium being more effective. The enhancement effect was related to the ability of calcium and magnesium to shift low molecular weight fractions of bacterial materials to more hydrophobic and larger molecular weight fractions. Bacterial materials developed with humic acid as carbon source contained more hydrophobic and larger molecular weight fractions, hence had higher DBPFP than bacterial materials developed with acetate. DBPs yields of bacterial materials were lower than that of NOMs precursor during chlorination, but during chloramination DBPs yields of bacterial materials were higher. The extracellular polymeric substances (EPS) matrix had higher DBPs yield than biofilm cells. Polysaccharide was more likely to be the main DBPs precursor in the EPS matrix.

High molecular weight components of natural organic matter preferentially adsorb onto nanoscale zero valent iron and magnetite

Nanoscale zero valent iron particles (nano-Fe0) are attractive for in-situ groundwater remediation due to their high reactivity and ability to degrade many different classes of environmental contaminants. It is expected that adsorbed natural organic matter (NOM), which is heterogeneous and typically has a wide molecular weight (MW) distribution, will affect the reactivity and performance of nano-Fe0 as a remediation agent. However, the interaction of NOM with nano-Fe0 has not been well-studied. In this study, we used high performance size exclusion chromatography (HPSEC) to determine if there was preferential sorption of the high MW fraction of NOM onto nano-Fe0 that have a Fe0 core and a Fe-oxide shell (predominantly magnetite). Adsorption of two types of NOM, Suwannee River Humic Acid (SRHA) and Fulvic Acid (SRFA), to nano-Fe0 was compared to magnetite of similar size (nano-Fe3O4) to also assess the effect of the Fe0 core on adsorption of NOM. The results showed that the surface area normalized adsorbed mass (mg/m2) of both SRHA and SRFA onto nano-Fe0 is almost three times than that of nano-Fe3O4. This is attributed to a greater number of reactive sites on nano-Fe0 compared to nano-Fe3O4, and indicates that the surface properties of nano-Fe0 are different that nano-Fe3O4 despite the shell of magnetite on nano-Fe0. The sorption capacity of both SRHA and SRFA onto nano-Fe0 were similar. However, the intermediate sized MW fractions (2–6 kDa) of SRHA were preferentially adsorbed onto the nano-Fe0 surface, whereas the large MW fractions (>3.5 kDa) of SRFA were preferentially adsorbed. These results suggest that NOM interaction with nano-Fe0 are a function of the MW distribution of the NOM in the system studied and indicate that the MW distributions of NOM should be taken into consideration when predicting the fate and performance of nano-Fe0 in environmental remediation.

Limited effects of land use on soil dissolved organic matter chemistry as assessed by excitation–emission fluorescence spectroscopy and molecular weight fractionation

AbstractDissolved organic matter (DOM) in soil solution represents a complex mixture of organic molecules and plays a central role in carbon and nitrogen cycling in plant–microbial–soil systems. We tested whether excitation–emission matrix (EEM) fluorescence spectroscopy can be used to characterize DOM and support previous findings that the majority of DOM is of high molecular weight (MW). EEM fluorescence spectroscopy was used in conjunction with MW fractionation to characterize DOM in soil solution from a grassland soil land management gradient in North Wales, UK. Data analysis suggested that three distinct fluorescence components could be separated and identified from the EEM data. These components were identified as being of humic‐like or fulvic‐like origin. Contrary to expectations, the majority of the fluorescence signal occurred in the small MW (&lt;1 kDa) fraction, although differences between soils from the differently managed grasslands were more apparent in larger MW fractions. We conclude that following further characterization of the chemical composition of the fluorophores, EEM has potential as a sensitive technique for characterizing the small MW phenolic fraction of DOM in soils.

Lignosulfonate To Enhance Enzymatic Saccharification of Lignocelluloses: Role of Molecular Weight and Substrate Lignin

This study conducted an investigation of the effect of lignosulfonate (LS) on enzymatic saccharification of lignocelluloses. Two commercial LSs and one laboratory sulfonated kraft lignin were applied to Whatman paper, dilute acid and SPORL (sulfite pretreatment to overcome recalcitrance of lignocelluloses) pretreated aspen, and kraft alkaline and SPORL pretreated lodgepole pine. All three lignin samples inhibited cellulose saccharification of Whatman paper, but enhanced the saccharification of the four lignocellulosic substrates. The level of enhancement was related to the molecular weight and degree of sulfonation of the lignin as well as the substrate lignin structure. When different molecular weight (MW) fractions of one commercial LS (SXP), generated from sulfite pulping of hardwood, were applied to the Whatman paper, the large MW fraction (SXP1) with the lowest degree of sulfonation inhibited cellulose saccharification while the intermediate (SXP2) and smallest (SXP3) MW fractions enhanced saccharification. All MW fractions enhanced saccharification of the four lignocellulosic substrates with maximal enhancement by the smallest MW fraction, SXP3. The enhancement was most significant for the kraft lodgepole pine substrate and least significant for the SPORL pretreated lodgepole pine using all three LS and SXP fractions. The results suggest that LS acts as a surfactant to enhance pure cellullose saccharification. When LS is applied to lignocelluloses, it acts as a surfactant to block bound lignin from binding cellulase nonproductively leading to enhanced saccharification.

Effect of molecular architecture on the crystalline structure and stiffness of iPP homopolymers: Modeling based on annealing experiments

ABSTRACTFive polypropylene (PP) homopolymers were selected and their molecular structure was thoroughly characterized to determine the effect of molecular architecture on their annealing behavior and on the ultimate stiffness achieved by heat treatment. Molecular mass and its distribution were characterized by rheological measurements, while chain regularity was determined by differential scanning calorimetry (DSC) using stepwise isothermal segregation technique (SIST). The samples were annealed in two different ways. Tensile bars were treated in an oven at 165 °C for increasing times to determine changes in stiffness. Various defects (microcracks and voids) developed during the annealing of tensile specimens that did not allow the reliable determination of modulus by direct measurement. On the other hand, the second approach, the annealing of small samples in a DSC cell clearly showed the changes occurring in crystalline structure and also the effect of nucleation and molecular architecture on them. The large molecular weight fraction used to facilitate nucleation hinders crystal perfection, whereas the presence of a heterogeneous nucleating agent increases overall crystallinity, but does not influence recrystallization during annealing. Melting traces were transformed into lamella thickness distributions from which average lamella thickness was derived. Lamella thickness and crystallinity, the independent variables of the model equation used for the calculation of modulus, were extrapolated to infinite annealing time to predict maximum stiffness. The value obtained, 3.5 GPa, is very far from the theoretically predicted 40 GPa of oriented crystals, which cannot be achieved under practical conditions. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3365–3373, 2013

A Zebrafish Model for Uremic Toxicity: Role of the Complement Pathway

Many organic solutes accumulate in end-stage renal disease (ESRD) and some are poorly removed with urea-based prescriptions for hemodialysis. However, their toxicities have been difficult to assess. We have employed an animal model, the zebrafish embryo, to test the toxicity of uremic serum compared to control. Serum was obtained from stable ESRD patients predialysis or from normal subjects. Zebrafish embryos 24 h postfertilization were exposed to experimental media at a water:human serum ratio of 3:1. Those exposed to serum from uremic subjects had significantly reduced survival at 8 h (19 ± 18 vs. 94 ± 6%, p < 0.05, uremic serum vs. control, respectively). Embryos exposed to serum from ESRD subjects fractionated at 50 kDa showed significantly greater toxicity with the larger molecular weight fraction (83 ± 11 vs. 7 ± 17% survival, p < 0.05, <50 vs. >50 kDa, respectively). Heating serum abrogated its toxicity. EDTA, a potent inhibitor of complement by virtue of calcium chelation, reduced the toxicity of uremic serum compared to untreated uremic serum (96 ± 5 vs. 28 ± 20% survival, p < 0.016, chelated vs. nonchelated serum, respectively). Anti-factor B, a specific inhibitor of the alternative complement pathway, reduced the toxicity of uremic serum, compared to untreated uremic serum (98 ± 6 vs. 3 ± 9% survival, p < 0.016, anti-factor B treated vs. nontreated, respectively). Uremic serum is thus more toxic to zebrafish embryos than normal serum. Furthermore, this toxicity is associated with a fraction of large size, is inactivated by heat, and is reduced by both specific and nonspecific inhibitors of complement activation. Together these data lend support to the hypothesis that at least some uremic toxicities may be mediated by complement.

Antioxidant capacities of fractionated barley hordein hydrolysates in relation to peptide structures

This study has revealed strong antioxidant activities of barley hordein hydrolysate fractions and investigated the relationships between antioxidant properties and structural features of hordein peptides. Barley hordein fractions separated based on molecular weight and surface hydrophobicity demonstrated strong antioxidant bioactivities, especially ferrous ion chelating capacity. Structural studies revealed the poly-l-proline helix, β-turn, and β-sheet as the dominant structural elements in the large molecular weight fraction, while most of the small-sized peptides assumed unordered random coil conformation accompanied by a large amount of ionized carboxyl groups produced as a result of partial deamidation of glutamine residues during hydrolysis. A study of antioxidant capacity in relation to peptide structure indicated the contribution of hydrophobic residues in radical scavenging and the positive effect of ionized carboxyl groups together with Lys and Met in metal chelation activity. QPYPQ was identified as the most repeated sequence in potent RP-HPLC fractions, which might be a particular structural motif that plays a key role in scavenging free radicals. Barley hordein with its unique sequence partitioning has potential to produce peptides with strong antioxidant bioactivities.

Characterization of dissolved organic matter as N-nitrosamine precursors based on hydrophobicity, molecular weight and fluorescence

It is very important to identify the dominant precursors for N-nitrosamine formation from bulk organic matter, to enhance the understanding of N-nitrosamine formation pathways in water treatment plants and allow the development of practical treatment technologies. In this study, dissolved organic matter (DOM) from two source waters was fractionated with XAD resins and ultrafiltration membranes. The N-nitrosamine formation potential (FP) (ng of N-nitrosamines formed per mg of dissolved organic carbon (DOC)) from raw water and each fraction were measured and correlated with the fluorescence excitation-emission matrix (EEM), molecular weight (MW) and other assays. The results showed that the hydrophilic fraction had N-nitrosamine FP 1.3 to 3.5 times higher than the hydrophobic fraction from both source waters. The DOM fraction with low MW was the dominant fraction in these two source waters and contributed more precursors for N-nitrosamine formation than the larger MW fraction. The EEM spectra indicated there were notable amounts of soluble microbial products (SMPs) and aromatic proteins in the two studied rivers, which probably originated from wastewater discharge. The SMPs tended to be more closely correlated with N-nitrosodimethylamine formation potential than the other DOM components. Higher N-nitrosamine FP were also related to fractions with lower DOC/DON ratios and lower SUVA254 values.

Transport behavior and deposition kinetics of humic acid under acidic conditions in porous media

The transport behavior of humic acid in porous media was studied from the viewpoint of colloidal stability. Column experiments were performed with a large molecular weight fraction of purified Aldrich humic acid over a wide range of monovalent (NaCl) and divalent (CaCl2) electrolyte concentrations at pH 3. The ratio of the humic acid effluent to influent concentration was analyzed using the colloid filtration theory to determine attachment efficiencies (α) of the humic acid that deposited onto the surface of glass beads. In a log–log plot, the obtained value of α increased linearly with an increase in the electrolyte concentrations up to a threshold value and remained constant above the threshold value for both NaCl and CaCl2. This threshold value represented the critical deposition concentration (CDC). The ratio of the CDC of NaCl to that of CaCl2 was reasonable as a prediction of the Schulze–Hardy rule. These findings suggest that the transport behavior of humic acid under acidic conditions depends on its colloidal stability.

Self-Assembled Tetranuclear Palladium Catalysts That Produce High Molecular Weight Linear Polyethylene

The phosphine-bis-arenesulfonate ligand PPh(2-SO(3)Li-4-Me-Ph)(2) (Li(2)[OPO]) coordinates as a kappa(2)-P,O chelator in Li[(Li-OPO)PdMe(Cl)] (2a) and (Li-OPO)PdMe(L) (L = pyridine (2b); MeOH (2d); 4-(5-nonyl)pyridine) (py', 3)). 2a reacts with AgPF(6) to form {(Li-OPO)PdMe}(n) (2c). Photolysis of 2d yields {(OPO)Pd}(2) (5) in which the [OPO](2-) ligand coordinates as a kappa(3)-O,P,O pincer. 3 self-assembles into a tetramer in which four (Li-OPO)PdMe(py') units are linked by Li-O bonds that form a central Li(4)S(4)O(12) cage. The Pd centers are equivalent but are spatially separated into two identical pairs. The Pd-Pd distance within each pair is 6.04 A. IR data (upsilon(ArSO(3)(-)) region) suggest that the solid state structures of 2a-c are similar to that of 3. 3 reacts with the cryptand Krypt211 to form [Li(Krypt211)][(OPO)PdMe(py')] (4). 3 is in equilibrium with a monomeric (Li-OPO)PdMe(py') species (3') in solution. 2a-c and 3 produce polyethylene (PE) with high molecular weight and a broad molecular weight distribution, characteristic of multisite catalysis. Under conditions where the tetrameric structure remains substantially intact, the PE contains a substantial high molecular weight fraction, while, under conditions where fragmentation is more extensive, the PE contains a large low molecular weight fraction. These results suggest that the tetrameric assembly gives rise to the high molecular weight polymer. In contrast, the monomeric complex 4, which contains a free pendant sulfonate group that can bind to Pd, oligomerizes ethylene to a Schultz-Flory distribution of C(4)-C(18) oligomers.