Time dependence of aldehyde and ketone oxocarboxylic acid photoproduct generation from crude oil-seawater systems under solar irradiation

Aldehyde and ketone oxocarboxylic acid photoproducts were semi-quantitated in the aqueous phase after subjecting Macondo (MC252) crude oil-seawater systems to simulated solar irradiation. Electrospray ionization tandem mass spectrometry (ESI-MS/MS) was applied after derivatizing the samples with 2,4-dinitrophenylhydrazine (DNPH). Oil-seawater was irradiated at 27.0 °C using a solar simulator for 1 to 18 h. Following irradiation, the aqueous phase was treated with DNPH to generate aldehyde-DNPH and ketone-DNPH derivatives. Solid-phase extraction enriched the samples before analyzing them using (-) ESI-MS/MS. Precursor and product ion spectra were used to select carboxylic acid-containing aldehydes and ketones and provide semi-quantitation using surrogate standards and an internal standard. Loss of m/z 44 (CO2) in the product ion spectra further confirmed the carboxylic acid character. Near-linear increases in photoproduct concentration in the aqueous phase were observed over the 18 h irradiation period. Among the aldehyde and ketone oxocarboxylic acid photoproducts studied, photoproduction rates ranged from 0.6 - 69 µmol/h·m2 of oil surface. Despite some fluctuations, a general trend of lower production rate with higher molecular weight was observed. These results demonstrate the near-linear dependence of photoproduction on irradiance and provide ranges of rates that can be applied to modeling aldehyde and ketone oxocarboxylic acid photoproduction in ocean spills. STATEMENT OF ENVIRONMENTAL IMPACT: Crude oil on seawater degrades when exposed to sunlight. Oxygenated molecules are produced, including carboxylic acid-containing aldehydes and ketones. The formation of these photoproducts from oil films behaves linearly with solar exposure time. These photoproducts are more soluble than the original oil molecules, allowing them to have increased bioavailability and potentially increased toxicity. The rate of formation of these species when oil is exposed to sunlight determines their environmental impact.

Dispersant-enhanced photodissolution of macondo crude oil: A molecular perspective

Previous laboratory studies developed a conceptual model based on elevated non-volatile dissolved organic carbon (NVDOC) concentrations after photodegradation and subsequent dissolution of Macondo oil following the Deepwater Horizon blowout. However, those experiments did not account for the effects of ∼1 million gallons of dispersant applied to the surface oil. Here, laboratory results show photodissolution in the presence of dispersant results in > 2x increase in NVDOC concentrations after extensive photoprocessing relative to oil without dispersant. This result corresponds with an apparent increase in the percentage of surface oil photodissolution from approximately 4% in the absence of dispersant to 7% in the presence of dispersant. The oil and dissolved products were analyzed by excitation-emission matrix spectroscopy and ultrahigh resolution mass spectrometry. The compounds that persisted in the oil phase are relatively aromatic without dispersant, while those in the presence of dispersant are highly aliphatic, paraffinic, wax-like compounds. The composition of the dissolved compounds produced from both treatment types are nearly identical after 240 h of exposure to simulated sunlight. The NVDOC and chemical composition information indicate that the photodissolution of MC252 oil in the presence of dispersant is enhanced and accelerated, suggesting that the effects of dispersants should be included in mass transfer calculations from the oil to the aqueous phase.

Photochemistry of oil in marine systems: developments since the Deepwater Horizon spill

Oil spills represent a major source of negative environmental impacts in marine systems. Despite many decades of research on oil spill behavior, photochemistry was neglected as a major factor in the fate of oil spilled in marine systems. Subsequent to the Deepwater Horizon oil spill, numerous studies using varied approaches have demonstrated the importance of photochemistry, including short-term impacts (hours to days) that were previously unrecognized. These studies have demonstrated the importance of photochemistry in the overall oil transformation after a spill and more specifically the impacts on emulsification, oxygenation, and microbial interactions. In addition to new perspectives, advances in analytical approaches have allowed an improved understanding of oil photochemistry after maritime spill. Although the literature on the Deepwater Horizon spill is extensive, this review focuses only on studies relevant to the advances in oil photochemistry understanding since the Deepwater Horizon spill.

Emerging Chemical Methods for Petroleum and Petroleum-Derived Dissolved Organic Matter Following the Deepwater Horizon Oil Spill

Despite the fact that oil chemistry and oils spills have been studied for many years, there are still emerging techniques and unknown processes to be explored. The 2010 Deepwater Horizon oil spill in the Gulf of Mexico resulted in a revival of oil spill research across a wide range of fields. These studies provided many new insights, but unanswered questions remain. Over 1,000 journal articles related to the Deepwater Horizon spill are indexed by the Chemical Abstract Service. Numerous ecological, human health, and organismal studies were published. Analytical tools applied to the spill include mass spectrometry, chromatography, and optical spectroscopy. Owing to the large scale of studies, this review focuses on three emerging areas that have been explored but remain underutilized in oil spill characterization: excitation-emission matrix spectroscopy, black carbon analysis, and trace metal analysis using inductively coupled plasma mass spectrometry.

Dissolved organic matter production from herder application and in-situ burning of crude oil at high latitudes: Bioavailable molecular composition patterns and microbial community diversity effects

Chemical herders and in-situ burning (ISB) are designed to mitigate the effects that oil spills may have on the high latitude marine environment. Little information exists on the water solubilization of petroleum residues stemming from chemically herded ISB and whether these bioavailable compounds have measurable impacts on marine biota. In this experiment, we investigated the effects of Siltech OP40 and crude oil ISB on a) petroleum-derived dissolved organic matter (DOM_HC) composition and b) seawater microbial community diversity over 28 days at 4 °C in aquarium-scale mesocosms. Ultra-high resolution mass spectrometry and fluorescence spectroscopy revealed increases in aromaticity over time, with ISB and ISB+OP40 samples having higher % aromatic classes in the initial incubation periods. ISB+OP40 contained a nearly 12-fold increase in the number of DOM_HC formulae relative to those before ISB. 16S rRNA gene sequencing identified differences in microbial alpha diversity between seawater, ISB, OP40, and ISB+OP40. Microbial betadiversity shifts were observed that correlated strongly with aromatic/condensed relative abundance and incubation time. Proteobacteria, specifically from the genera Marinomonas and Perlucidibaca experienced -22 and +24 log₂-fold changes in ISB+OP40 vs. seawater, respectively. These findings provide an important opportunity to advance our understanding of chemical herders and ISB in the high latitude marine environment.

Barium ion adduct mass spectrometry to identify carboxylic acid photoproducts from crude oil-water systems under solar irradiation

Petroleum derived dissolved organic matter (DOMHC) samples were successfully cationized with barium, revealing many [M-H + Ba]+ peaks in both dark and simulated sunlight treatments. The DOMHC samples generated after light exposure exhibited a greater number of [M-H + Ba]+ peaks compared to the dark control. Multiple [M-H + Ba]+ peaks were investigated in the irradiated DOMHC using low resolution MS/MS in order to confirm the presence of diagnostic fragment ions, m/z 139, 155 and 196 in each treatment. Due to the high complexity of the bariated DOMHC mixture, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS/MS) was employed to obtain molecular level information for both irradiated and dark treatments. The irradiated DOMHC treatments had more bariated oxygenated species over a wide range of H/C and O/C when compared to the dark controls. Doubly bariated species were also observed in DOMHC, which provides evidence that photochemistry transforms DOMHC to even more complex mixtures with multiple oxygenations per molecule. This study provides evidence that barium adduct mass spectrometry can be successfully applied to DOMHC screening for the presence of COOHs, both in dark samples and solar irradiated samples. Furthermore, direct evidence and molecular composition of aqueous phase crude oil photoproducts is provided by this technique.

Molecular-Level Composition and Acute Toxicity of Photosolubilized Petrogenic Carbon

To examine the molecular-level composition and acute toxicity per unit carbon of the petroleum-derived dissolved organic matter (DOM_HC) produced via photo-oxidation, heavy and light oils were irradiated over seawater with simulated sunlight. Increases in dissolved organic carbon concentrations as a function of time were associated with changes in the DOM_HC composition and acute toxicity per unit carbon. Parallel factor analysis showed that the fluorescent dissolved organic matter (FDOM) composition produced from the heavy oil became more blue-shifted over time, while the light oil produced a mixture of blue- and red-shifted components similar to FDOM signatures. Ultrahigh-resolution mass spectrometry reveals that the composition of the DOM_HC produced from both heavy and light oils was initially relatively reduced, with low O/C. With time, the composition of the DOM_HC produced from the heavy oil shifted to unsaturated, high-oxygen compounds, while that produced from the light oil comprised a range of high O/C aliphatic, unsaturated, and aromatic compounds. Microtox assays suggest that the DOM_HC initially produced is the most toxic (62% inhibition); however, after 24 h, a rapid decrease in toxicity decreased linearly to 0% inhibition for the heavy DOM_HC and 12% inhibition for the light DOM_HC at extended exposure periods.

Aldehyde and Ketone Photoproducts from Solar-Irradiated Crude Oil-Seawater Systems Determined by Electrospray Ionization-Tandem Mass Spectrometry

Aldehyde and ketone photoproducts were observed in the aqueous phase under oil exposed to simulated sunlight by using 2,4-dinitrophenylhydrazine (DNPH) derivatization and electrospray ionization-tandem mass spectrometry (ESI-MS/MS). Oil samples were spread over seawater in a jacketed beaker held at 27.0 °C and exposed to simulated sunlight. The aqueous phase was collected after irradiation and derivatized with DNPH, which selectively reacts with aldehydes and ketones. The derivatized hydrazones (aldehyde- and ketone-DNPH derivatives) were washed and enriched with a solid-phase extraction cartridge prior to analysis by ESI-MS/MS in negative ion mode. Over 80 aldehyde and ketone photoproducts were observed from scan range 200-1000 atomic mass units (amu) in the aqueous phase after irradiation but were absent in dark controls. Based on the MS/MS fragmentation of the aldehyde- and ketone-DNPH derivatives, most of the aldehyde and ketone photoproduct mass spectra observed from the aqueous phase were determined to be consistent with dicarbonyls, hydroxycarbonyls, and oxo-carboxylic acids. The formation of the photoproducts can be attributed to photoinduced oxidation of oil. The approach in this study allows the easy identification of molar mass and other structural features of aldehyde and ketone photoproducts without interference from the many tens of thousands of parent compounds in the oil. These results will provide insight into the impact of photochemistry on the fate of oil in environmental systems and will have implications for oil-spill response decisions.

Impact of Photooxidation and Biodegradation on the Fate of Oil Spilled During the Deepwater Horizon Incident: Advanced Stages of Weathering

While the biogeochemical forces influencing the weathering of spilled oil have been investigated for decades, the environmental fate and effects of "oxyhydrocarbons" in sand patties deposited on beaches are not well-known. We collected sand patties deposited in the swash zone on Gulf of Mexico beaches following the Deepwater Horizon oil spill. When sand patties were exposed to simulated sunlight, a larger concentration of dissolved organic carbon was leached into seawater than the corresponding dark controls. This result was consistent with the general ease of movement of seawater through the sand patties as shown with a ³⁵SO₄^2- radiotracer. Ultrahigh-resolution mass spectrometry, as well as optical measurements revealed that the chemical composition of dissolved organic matter (DOM) leached from the sand patties under dark and irradiated conditions were substantially different, but neither had a significant inhibitory influence on the endogenous rate of aerobic or anaerobic microbial respiratory activity. Rather, the dissolved organic photooxidation products stimulated significantly more microbial O₂ consumption (113 ± 4 μM) than either the dark (78 ± 2 μM) controls or the endogenous (38 μM ± 4) forms of DOM. The changes in the DOM quality and quantity were consistent with biodegradation as an explanation for the differences. These results confirm that sand patties undergo a gradual dissolution of DOM in both the dark and in the light, but photooxidation accelerates the production of water-soluble polar organic compounds that are relatively more amenable to aerobic biodegradation. As such, these processes represent previously unrecognized advanced weathering stages that are important in the ultimate transformation of spilled crude oil.

Cleavable ester linked magnetic nanoparticles for labeling of solvent exposed primary amine groups of peptides/proteins

Covalent labeling of solvent exposed amino acid residues using chemical reagents/crosslinkers followed by mass spectrometric analysis can be used to determine the solvent accessible amino acids of a protein. A variety of chemical reagents containing cleavable bonds were developed to label abundantly found lysine residues on the surface of protein. To achieve efficient separation of labeled peptides prior to mass spectrometric analysis, magnetic nanoparticles can be decorated with amino acid reactive functional groups and utilized for quick recovery of labeled peptides. [1] In this work, iron oxide magnetic nanoparticles (Fe3O4 MNPs) were synthesized by thermal decomposition method and coated with silica (SiO2@Fe3O4 MNPs) by reverse micro emulsion approach. The Fe3O4 MNPs and SiO2@Fe3O4 MNPs were characterized by TEM and XRD. The SiO2@Fe3O4 MNPs were further coated with amine groups and conjugated to N-hydroxysuccinimidyl (NHS) ester groups via a cleavable ester bond. Fluorescence based qualitative analysis of ester linked NHS ester modified SiO2@Fe3O4 MNPs was performed to confirm the presence of NHS ester group. The active NHS ester sites on the surface of SiO2@Fe3O4 MNPs were determined by depletion approach and found to be 694 active sites per 1 mg of SiO2@Fe3O4 MNPs. Free amine groups of a small peptide, ACTH (4-11) were labeled by ester linked, NHS ester modified SiO2@Fe3O4 MNPs under physiological conditions. Superparamagnetic nature of SiO2@Fe3O4 MNPs allowed quick and efficient magnetic separation of labeled peptides from the solution. The ester bond was further cleaved to separate labeled peptides followed by mass spectrometric analysis. The ester linked, NHS ester modified SiO2@Fe3O4 MNPs introduced a mass shift of 115.09 Da on amine groups of ACTH (4-11), which was confirmed by mass spectrometry.

Cleavable ester-linked magnetic nanoparticles for labeling of solvent-exposed primary amine groups of peptides/proteins

To study the solvent-exposed lysine residues of peptides/proteins, we previously reported disulfide-linked N-hydroxysuccinimide ester-modified silica-coated iron oxide magnetic nanoparticles (NHS-SS-SiO2@Fe3O4 MNPs). The presence of a disulfide bond in the linker limits the use of disulfide reducing agent during protein digestion and allows unwanted disulfide formation between the MNPs and protein. In the current work, the disulfide bond was replaced with a cleavable ester group to synthesize NHS ester-modified SiO2@Fe3O4 MNPs. Use of the cleavable ester group provides an improved method for protein labeling and allows the use of disulfide reducing agents during protein digestion.

Hybrid paclitaxel and gold nanorod-loaded human serum albumin nanoparticles for simultaneous chemotherapeutic and photothermal therapy on 4T1 breast cancer cells

The use of human serum albumin nanoparticles (HSAPs) as a drug carrier system for cancer treatment has proven successful through current marketable clinical formulations. Despite this success, there is a current lack of multifunctional HSAPs, which offer combinational therapies of more than one proven technique. Gold nanorods (AuNRs) have also shown medicinal promise due to their photothermal therapy capabilities. In this study, a desolvation and cross-linking approach was employed to successfully encapsulate gold nanorods into HSAPs simultaneously with the chemotherapeutic drug paclitaxel (PAC); forming PAC-AuNR-HSAPs with desirable overall particle sizes of 299 ± 6 nm. The loading efficiency of paclitaxel into PAC-AuNR-HSAPs reached up to 3 μg PAC/mg HSA. The PAC-AuNR-HSAPs experienced photothermal heating; with the bulk particle solution reaching up to 46 °C after 15 min of near-IR laser exposure. This heat increase marked the successful attainment of the temperature necessary to cause severe cellular hyperthermia and necrosis. The encasement strategy facilitated a colloidal hybrid treatment system capable of enhanced permeability and retention effects, photothermal ablation of cancer cells, and release of the active paclitaxel of up to 188 ng (from PAC-AuNR-HSAPs created with 30 mg HSA) in a single 15 min irradiation session. When treated with PAC-AuNR-HSAPs containing 20 μg PAC/mL particle solution, 4T1 mouse breast cancer cells experienced ∼82% cell death without irradiation and ∼94% cell death after just one irradiation session. The results for PAC-AuNR-HSAPs were better than that of free PAC, which only killed ∼77% of the cells without irradiation and ∼80% with irradiation. The hybrid particle system also lends itself to future customizable external functionalities via conjugated targeting ligands, such as antibodies. Internal entrapment of patient tailored medication combinations are also possible with this combination treatment platform, which may result in improved quality of life for those undergoing treatment.

In vitro oxidative footprinting provides insight into apolipoprotein B-100 structure in low-density lipoprotein

Low-density lipoprotein (LDL) is a major cholesterol carrier in human blood. Oxidations of apolipoprotein B-100 (apo B-100, LDL protein) could be proatherogenic and play critical roles in early stages of plaque formation in the arterial wall. The structure of apo B-100 is still poorly understood, partially due to its size (550 KDa, 4563 amino acids). To gain an insight into LDL structure, we mapped the regions of apo B-100 in human LDL that were prone to oxidation using peroxynitrite and hypochlorite as probes. In this study, LDL was incubated with various concentrations of peroxynitrite and sodium hypochlorite in bicarbonate buffer. The LDL protein apo B-100 was delipidated, denatured, alkylated, and subjected to tryptic digestion. Tryptic peptides were analyzed employing LC-MS/MS. Database search was performed against the apo B-100 database (SwissProt accession #P04114) using "SEQUEST" algorithm to identify peroxynitrite and hypochlorite-mediated oxidations markers nitrotyrosine, nitrotryptophan, hydroxy-tryptophan, and 3-chlorotyrosine. Several site-specific oxidations were identified in apo B-100 after treatment of intact LDL particles with the oxidants. We hypothesize that these regions could be accessible to oxidant and critical for early events in atherosclerotic plaque deposition.

Sunlight creates oxygenated species in water-soluble fractions of Deepwater Horizon oil

In order to assess the impact of sunlight on oil fate, Macondo well oil from the Deepwater Horizon (DWH) rig was mixed with pure water and irradiated with simulated sunlight. After irradiation, the water-soluble organics (WSO) from the dark and irradiated samples were extracted and characterized by ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Liquid-liquid extraction yielded two fractions from dark and irradiated water/oil mixtures: acidic WSOs (negative-ion electrospray (ESI)), and base/neutral WSOs (positive-ion ESI) coupled to FT-ICR MS to catalog molecular-level transformations that occur to Macondo-derived WSOs after solar irradiation. Such direct measure of oil phototransformation has not been previously reported. The most abundant heteroatom class detected in the irradiated WSO acid fractions correspond to molecules that contain five oxygens (O5), while the most abundant acids in the dark samples contain two oxygen atoms per molecule (O2). Higher-order oxygen classes (O5-O9) were abundant in the irradiated samples, but <1.5% relative abundance in the dark sample. The increased abundance of higher-order oxygen classes in the irradiated samples relative to the dark samples indicates that photooxidized components of the Macondo crude oil become water-soluble after irradiation. The base/neutral fraction showed decreased abundance of pyridinic nitrogen (N1) concurrent with an increased abundance of N1Ox classes after irradiation. The predominance of higher-order oxygen classes indicates that multiple photochemical pathways exist that result in oxidation of petroleum compounds.

Petroleum films exposed to sunlight produce hydroxyl radical

Sunlight exposed oil films on seawater or pure water produced substantial amounts of hydroxyl radical as a result of irradiation. Oil was collected from the surface of the Gulf of Mexico following the Deepwater Horizon spill and exposed to simulated sunlight in thin films over water. Photochemical production of hydroxyl radical was measured with benzoic acid as a selective chemical probe in the aqueous layer. Total hydroxyl radical formation was studied using high benzoic acid concentrations and varying exposure time. The total amount of hydroxyl radical produced in 24 h irradiations of thin oil films over Gulf of Mexico water and pure water were 3.7×10(-7) and 4.2×10(-7) moles respectively. Steady state concentrations of hydroxyl radical were measured using a competition kinetics approach. Hydroxyl radical concentrations of 1.2×10(-16) to 2.4×10(-16) M were observed for seawater and pure water under oil films. Titanium dioxide (TiO2) nanomaterials were added to the system in an effort to determine if the photocatalyst would enhance oil photodegradation. The addition of TiO2 nanoparticles dramatically changed the observed formation rate of hydroxyl radical in the systems with NP water at pH 3, showing increased formation rate in many cases. With photocatalyst, the steady state concentration of radical decreased, predominantly due to an increase in the hydroxyl radical scavenging rate with oxide present. This study illustrates that oil is a strong and important source of hydroxyl radical when exposed to sunlight. The fate of oil and other dissolved species following oil spills will be heavily dependent on the formation and fate of hydroxyl radical.

Photolytic and photocatalytic degradation of surface oil from the Deepwater Horizon spill

The photochemical behavior of Deepwater Horizon oil collected from the surface of the Gulf of Mexico was studied. Thin oil films on water were subjected to simulated sunlight, and the resulting chemical and optical changes were observed. Polycyclic aromatic hydrocarbons (PAHs) showed substantial photodegradation, with larger PAHs being more rapidly decomposed. About 60% of the fluorescence at the excitation and emission maxima was observed with 12h of simulated solar irradiation equivalent to approximately 3d of sunlight. Synchronous scan fluorescence measurements showed 80-90% loss of larger PAHs with 12h of simulated solar irradiation. Absorbance of the oil decreased by only 20% over the same time period. Alkanes showed no significant photochemical losses. After irradiation, the toxicity of water in contact with the oil significantly increased, presumably due to the release of water soluble photoproducts that were toxic. Photocatalyst addition resulted in enhanced degradation rate for PAHs, and toxicity of the aqueous layer was altered in the presence of photocatalysts added to the oil film. Photochemistry is an important pathway for degradation of large PAHs, which are typically resistant to biodegradation.

Labeling primary amine groups in peptides and proteins with N-hydroxysuccinimidyl ester modified Fe3O4@SiO2 nanoparticles containing cleavable disulfide-bond linkers

The surface of superparamagnetic silica coated iron oxide (Fe3O4@SiO2) nanoparticles was functionalized with a disulfide bond linked N-hydroxysuccinimidyl (NHS) ester group in order to develop a method for labeling primary amines in peptides/proteins. The nanoparticle labeled proteins/peptides formed after NHS ester reaction with the primary amine groups were isolated using a magnet without any additional purification step. Nanoparticle moieties conjugated to peptides/proteins were then trimmed by cleavage at the disulfide linker with a reducing agent. The labeled peptides were analyzed by LC-MS/MS to determine their sequences and the sites of NHS ester labeling. This novel approach allowed characterization of lysine residues on the solvent accessible surface of native bovine serum albumin. Low cost, rapid magnetic separation, and specificity toward primary amine groups make NHS ester coated Fe3O4@SiO2 nanoparticles a potential labeling probe to study proteins on living cell surfaces.

Laser-induced oxidation of cholesterol observed during MALDI-TOF mass spectrometry

Conditions for the detection of three odd-electron cholesterol oxidation peaks were determined and these peaks were shown to be artifacts of the matrix-assisted laser desorption time of flight (MALDI-TOF) process. Matrix choice, solvent, laser intensity and cholesterol concentration were systematically varied to characterize the conditions leading to the highest signals of the radical cation peaks, and it was found that initial cholesterol solution concentration and resultant density of solid cholesterol on the MALDI target were important parameters in determining signal intensities. It is proposed that hydroxyl radicals, generated as a result of laser irradiation of the employed 2,5-dihydroxybenzoic acid (DHB) matrix, initiate cholesterol oxidation on the MALDI target. An attempt to induce the odd-electron oxidation peaks by means of adding an oxidizing agent succeeded using an acetonitrile solution of DHB, cholesterol, and cumene hydroperoxide. Moreover, addition of free radical scavengers reduced the abundances of some oxidation products under certain conditions. These results are consistent with the mechanism of oxidation proposed herein involving laser-induced hydroxyl radical production followed by attack on neutral cholesterol. Hydroxyl radical production upon irradiation of dithranol matrix may also be responsible for generation of the same radical peaks observed from cholesterol in dithranol by an analogous mechanism.

Mapping oxidations of apolipoprotein B-100 in human low-density lipoprotein by liquid chromatography-tandem mass spectrometry

Human low-density lipoprotein (LDL) is a major cholesterol carrier in blood. Elevated concentration of low-density lipoprotein, especially when oxidized, is a risk factor for atherosclerosis and other cardiac inflammatory diseases. Past research has connected free radical initiated oxidations of LDL with the formation of atherosclerotic lesions and plaque in the arterial wall. The role of LDL protein in the associated diseases is still poorly understood, partially due to a lack of structural information. In this study, LDL was oxidized by hydroxyl radical. The oxidized protein was then delipidated and subjected to trypsin digestion. Peptides derived from trypsin digestion were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Identification of modified peptide sequences was achieved by a database search against apo B-100 protein sequences using the SEQUEST algorithm. At different hydroxyl radical concentrations, oxidation products of tyrosine, tryptophan, phenylalanine, proline, and lysine were identified. Oxidized amino acid residues are likely located on the exterior of the LDL particle in contact with the aqueous environment or directly bound to the free radical permeable lipid layer. These modifications provided insight for understanding the native conformation of apo B-100 in LDL particles. The presence of some natural variants at the protein level was also confirmed in our study.

Characterization of an NF-kappaB-regulated, miRNA-146a-mediated down-regulation of complement factor H (CFH) in metal-sulfate-stressed human brain cells

Micro RNAs (miRNAs) represent a family of small ribonucleic acids (RNAs) that are post-transcriptional regulators of messenger RNA (mRNA) complexity. Brain cells maintain distinct populations of miRNAs that support physiologically normal patterns of expression, however, certain miRNA abundances are significantly altered in neurodegenerative disorders such as Alzheimer's disease (AD). Here we provide evidence in human neural (HN) cells of an aluminum-sulfate- and reactive oxygen species (ROS)-mediated up-regulation of an NF-kappaB-sensitive miRNA-146a that down-regulates the expression of complement factor H (CFH), an important repressor of inflammation. This NF-kappaB-miRNA-146a-CFH signaling circuit is known to be similarly affected by Abeta42 peptides and in AD brain. These aluminum-sulfate-inducible events were not observed in parallel experiments using iron-, magnesium-, or zinc-sulfate-stressed HN cells. An NF-kappaB-containing miRNA-146a-promoter-luciferase reporter construct transfected into HN cells showed significant up-regulation of miRNA-146a after aluminum-sulfate treatment that corresponded to decreased CFH gene expression. These data suggest that (1) as in AD brain, NF-kappaB-sensitive, miRNA-146a-mediated, modulation of CFH gene expression may contribute to inflammatory responses in aluminum-stressed HN cells, and (2) underscores the potential of nanomolar aluminum to drive genotoxic mechanisms characteristic of neurodegenerative disease processes.

Covalently bound fluorescent probes as reporters for hydroxyl radical penetration into liposomal membranes

The ability of hydroxyl radicals to penetrate into liposomal model membranes (dimyristoylphosphatidylcholine) has been demonstrated. Liposomes were prepared and then characterized by digital fluorescence microscopy and dynamic light scattering after extrusion to determine liposomal lamellarity, size, and shape. Hydroxyl radicals were generated in the surrounding aqueous medium using a modified Fenton reagent (hydrogen peroxide and Fe(2+)) with the water-soluble iron chelator EDTA. High and low doses of radical were used, and the low dose was achieved with physiologically relevant iron and peroxide concentrations. Fluorescent probes covalently bound to the membrane phospholipid were used, including two lipophilic pyrenyl probes within the membrane bilayer and one polar probe at the water-membrane interface. Radical reactions with the probes were monitored by following the decrease in fluorescence and by observing oxidation products via matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Differences in the probe position within the membrane were correlated with the reactivity of the probe to assess radical access to the site of the probe. For all probes, reaction rates increased with increasing temperature. Within the membrane bilayer, reaction rates were greater for the probe closest to the membrane-water interface. Cholesterol protected these probes from oxidation. Kinetic models, scavenger studies, and product identification studies indicated that hydroxyl radical reacted directly with the in-membrane probes without the mediation of a secondary radical.

Gold-magnetite nanocomposite materials formed via sonochemical methods

Treatment of preformed magnetite nanoparticles with ultrasound in aqueous media with dissolved tetrachloroauric acid resulted in the formation of gold-magnetite nanocomposite materials. These materials maintained the morphology of the original magnetite particles. The loading of gold particles could be controlled by adjusting experimental parameters, including the addition of small amounts of solvent modifiers such as methanol, diethylene glycol, and oleic acid. The nanocomposite materials were magnetic and exhibited optical properties similar to pure gold nanoparticles.

Fluoride detection based on fluorescence enhancement of thioureido naphthalene derivative

A novel thioureido naphthalene derivative was synthesized and characterized. The compound proved itself as an effective fluoride sensor with respect to selectivity and sensitivity. In acetonitrile, the fluorescence intensity increased by 40-fold with the addition of 5 equiv. of fluoride. Fluorescence intensity did not substantially change with other halides, suggesting that the thioureido protons interact strongly with fluoride but not with other halides. The enhanced fluorescence is due to increased quantum efficiency of the fluoride complex.Key words: fluoride sensing, thioureido compound, fluorescence.

Assessment of ternary iron-cyclodextrin-2-naphthol complexes using NMR and fluorescence spectroscopies

Recent research has indicated that ternary complexes can be formed among carboxymethyl-beta-cyclodextrin, certain polycyclic aromatic hydrocarbons (PAHs) (e.g. anthracene and 2-naphthol), and Fe(2+) in aqueous solution. The formation of these ternary complexes has been suggested as the reason for improved reaction efficiency in iron catalyzed Fenton degradation (H(2)O(2)+Fe(2+)-->*OH+OH(-)+Fe(3+)) of PAHs and other pollutants. In the present work, several other cyclodextrins were examined to determine their ability to form similar ternary complexes with 2-naphthol and Fe(2+). Fluorescence and NMR techniques were employed in this study. Results showed that hydroxypropyl-beta-cyclodextrin, beta-cyclodextrin, and alpha-cyclodextrin were able to encapsulate 2-naphthol molecules, but their binding with Fe(2+) was weak. On the contrary, sulfated-beta-cyclodextrin has significant binding with Fe(2+), but it showed little inclusion of 2-naphthol molecules. Consequently, none of these four cyclodextrins formed significant amounts of ternary complexes in aqueous solution. The techniques used in this study provide useful methods for assessing the ability of cyclodextrins to form ternary complexes with guest compounds and metal ions.

Synergistic effects of iron and aluminum on stress-related gene expression in primary human neural cells

Disturbances in metal-ion transport, homeostasis, overload and metal ion-mediated catalysis are implicated in neurodegenerative conditions such as Alzheimer's disease (AD). The mechanisms of metal-ion induced disruption of genetic function, termed genotoxicity, are not well understood. In these experiments we examined the effects of non-apoptotic concentrations of magnesium-, iron- and aluminum-sulfate on gene expression patterns in untransformed human neural (HN) cells in primary culture using high density DNA array profiling and Western immunoassay. Two week old HN cells were exposed to low micromolar magnesium, iron, or aluminum for 7 days, representing trace metal exposure over one-third of their lifespan. While total RNA yield and abundance were not significantly altered, both iron and aluminum were found to induce HSP27, COX-2, betaAPP and DAXX gene expression. Similarly up-regulated gene expression for these stress-sensing, pro-inflammatory and pro-apoptotic elements have been observed in AD brain. The combination of iron and aluminum together was found to be particularly effective in up-regulating these genes, and was preceded by the evolution of reactive oxygen intermediates as measured by 2',7'-dichlorofluorescein diacetate assay. These data indicate that physiologically relevant amounts of iron and aluminum are capable of inducing Fenton chemistry-triggered gene expression programs that may support downstream pathogenic responses and brain cell dysfunction.

Enhancement of sonochemical degradation of phenol using hydrogen atom scavengers

Sonochemical degradation of phenol was found to be enhanced in the presence of the volatile hydrogen atom scavengers CCl4 and perfluorohexane. The non-volatile hydrogen atom scavenger iodate did not enhance phenol degradation. The first order rate constant for aqueous phenol degradation in separate experiments using different sonochemical probes increased in the presence of 150 microM CCl4 from 0.014 to 0.031 min(-1) (probe 1) and from 0.022 to 0.061 min(-1) (probe 2). In the presence of <1.5 microM C6H14, the first order rate constant increased from 0.014 to 0.032 min(-1) (probe 1). Hydroquinone was the major observed reaction intermediate both in the presence and absence of hydrogen atom scavengers. Hydroquinone yields were substantially higher in the presence of hydrogen atom scavengers, suggesting that hydroxyl radical pathways for phenol degradation were enhanced by the hydrogen atom scavengers. These additives may be useful in improving pollutant degradation efficiency or improving synthetic processes that rely on hydroxyl radical as a key intermediate.

A novel fluoride sensor based on fluorescence enhancement

A novel halide sensor, which yields greater fluorescence upon binding to fluoride, has been synthesized and characterized.

Enhanced Fenton degradation of hydrophobic organics by simultaneous iron and pollutant complexation with cyclodextrins

The effectiveness and selectivity of Fenton degradation of hydrophobic organic compounds (HOCs) can be improved by simultaneous complexation of Fe(2+) and the organic compound with a cyclodextrin or derivatized cyclodextrin. Such selective complexation of a target substrate and a catalytic metal is a crude mimic of enzyme systems. Both beta-cyclodextrin and carboxymethyl-beta-cyclodextrin (CMCD) were able to simultaneously complex Fe(2+) and an aromatic hydrocarbon, such as phenol, polycyclic aromatic hydrocarbons, and polychlorinated biphenyls (PCBs). Degradation of compounds included in cyclodextrins was unaffected by hydroxyl radical scavengers, indicating that the radical was formed at the ternary complex (HOC-cyclodextrin-iron) and in close proximity to the included molecule. Without cyclodextrins, humic acid (HA) decreased degradation efficiency. However, in the presence of CMCD, HA did not inhibit degradation of the target compound. CMCD is capable of removing HOCs from HA binding sites while at the same time complexing Fe(2+). PCBs sorbed to glass were resistant to Fenton degradation, but were significantly degraded using a cyclodextrin modified Fenton system. In all of these systems, the ternary HOC-cyclodextrin-iron complexes effectively direct hydroxyl radical reaction toward the HOC, increasing the efficiency of Fenton degradation. One potential application of such targeted degradation systems is the in situ remediation of hydrophobic organic pollutants in contaminated soil and groundwater or in industrial waste streams.

Dication induced stabilization of gas-phase ternary beta-cyclodextrin inclusion complexes observed by electrospray mass spectrometry

Electrospray mass spectrometry (ES-MS) is an important tool for characterization of non-covalent binding in the gas phase. In this study, iron (II) has been introduced as a dication to enhance the detection of cyclodextrin (CD) plus aromatic compound complexes in ES-MS. Evidence that a novel ternary complex comprised of one beta-CD, one iron (II) and one toluene exists as an inclusion complex has been compiled via ES-MS and ES-MS/MS experiments as well as by a computational approach. This evidence strongly suggests that iron (II) serves to modify the conformation of the beta-CD ring, and that toluene inclusion is stabilized by dication interaction with the toluene pi-system and by crimping of the beta-CD ring leading to stronger van der Waals interactions with toluene. Mg(II), another dication of similar radius, showed similar behavior, while added group one cations (H(+) and Na(+)) were ineffective at producing observable ions representative of the complex. The ternary beta-CD complex with iron (II) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) has also been examined. ES-MS and ES-MS/MS experiments suggest that it is the polar portion of 2,4,5-T (i.e., the carboxylic acid moiety) that is favored for inclusion in the beta-CD cavity, rather than the non-polar aromatic part.

Mechanisms of ammonia and amino acid photoproduction from aquatic humic and colloidal matter

Photochemical release of free amino acids was observed from dissolved fulvic acid (Suwannee River) and from colloidal fractions collected from Bayou Trepagnier, LA. Water samples were irradiated with a solar simulator, and free amino acid concentrations were determined using high performance liquid chromatography of the fluorescent derivitized amino acids. Increased concentrations of at least 20 amines were observed upon irradiation of water samples. Among the amino acids identified were alanine, asparagine, citrulline, glutamic acid, histidine, norvaline, and serine. Amino acid concentrations increased in the range of 0.03-9.5 nM h(-1). Studies on the mechanism of photochemical release of ammonia from dissolved natural organic matter (NOM) indicated at least two mechanisms. One mechanism proceeds through an hydroxyl radical intermediate. This mechanism continues in the dark after irradiation through decomposition of photochemically produced H2O2 to form hydroxyl radical. Although NOM photosensitized degradation of amino acids produces ammonia, amino acids do not appear to be an important intermediate in the photochemical formation of ammonia from NOM.

Aqueous sonolytic decomposition of polycyclic aromatic hydrocarbons in the presence of additional dissolved species

Sonochemical degradation of aqueous polycyclic aromatic hydrocarbons (PAHs) results in a first-order loss of the PAHs (k = 0.010-0.027 s-1). When sonication occurred in the presence of other organic compounds, the degradation rate constant was reduced quite dramatically. This reduction is believed to come about through scavenging of radicals by the matrix chemical. When oxygen was bubbled into the PAH solution before sonication, the degradation rate constant was elevated. Nitrogen purging resulted in decreased rate constants. These results indicate that oxygen was an important precursor in the degradation of the PAHs. Organic compounds, including humic acid, benzoic acid, and sodium dodecyl sulfate, decreased PAH degradation rate constants by scavenging oxygen derived reactive transients.

Quantitation of hydroxyl radical during fenton oxidation following a single addition of iron and peroxide

Chemical probes were used to study the formation of hydroxyl radical in aqueous iron-hydrogen peroxide reaction. Hydroxyl radical formation rate and time dependent concentration were determined in pure water, in aqueous fulvic acid (FA) and humic acid (HA) solutions, and in natural surface waters. Indirect determinations of hydroxyl radical were made by quantitating hydroxyl radical reactions with probe compounds under controlled conditions. High probe concentrations were used to determine radical formation rates and low probe concentrations were used to determine time dependent radical concentration. Two independent probes were used for intercomparison: benzoic acid and 1-propanol. Good agreement between the two probes was observed. Natural water matrices resulted in lower radical formation rates and lower hydroxyl radical concentrations, with observed formation rate and yield in natural waters up to four times lower than in pure water. HA and FA also reduced hydroxyl radical formation under most conditions, although increased radical formation was observed with FA at certain pH values. Hydroxyl radical formation increased linearly with hydrogen peroxide concentration.

Dissolved organic matter inhibition of sonochemical degradation of aqueous polycyclic aromatic hydrocarbons

Sonochemical degradation of aqueous polycyclic aromatic hydrocarbons (PAHs) was found to be rapid in the absence of other dissolved compounds (k = 0.006-0.015 s-1). In the presence of 20 mg Cl-1 fulvic acid, first-order PAH degradation rate constants decreased from 2.3- to 3.7-fold. Similar results were obtained with added benzoic acid, a crude analog for fulvic acid. In natural waters, PAH degradation was almost completely inhibited. Analysis of the kinetic behavior and reaction products indicates that PAHs are most likely degraded through a radical cation mechanism. Hydroxyl radical appeared to play an insignificant role in the degradation. Inhibited degradation was probably the result of either altered cavitation processes or isolation of the PAH away from cavitation sites.