Biomedical subjects

Patrick G Hatcher

Publications and source records attributed to Patrick G Hatcher.

23 records · Page 2Linked to original sources

PubMed2002

Phenanthrene sorption by aliphatic-rich natural organic matter.

Contaminant sorption, an important process that may limit bioavailability, hinder remediation, encourage environmental persistence, and control mobility in the environment, has been the focus of numerous studies. Despite these efforts, the fundamental understanding of sorptive processes in soil and sedimentary environments has not been resolved. For instance, many have suggested that contaminants, such as polycyclic aromatic hydrocarbons (PAHs), solely interact with aromatic domains of organic matter. Until now, studies have neglected the aliphatic components that are known to be a recalcitrant and significant part of soil and sedimentary organic matter (SOM). In this investigation, the sorption of phenanthrene to several aliphatic-rich SOM samples was measured. The samples included the following: SOM precursors (algae, degraded algae, cellulose, collagen, cuticle, and lignin), two kerogen samples, and a highly aromatic humic acid. All samples were characterized by cross polarization magic angle spinning carbon-13 (CPMAS 13C) NMR and carbon, hydrogen, and nitrogen analysis. Batch experiments demonstrated that the highest organic carbon normalized sorption coefficients (Koc values) were obtained with the Pula kerogen sample (log Koc = 4.88) that only contains 6.5% aromatic carbon. Other aliphatic-rich samples, namely the Green River kerogen, degraded algae, and collagen samples produced comparable log Koc values (4.64, 4.66, and 4.72, respectively) to that of the highly aromatic humic acid (log Koc = 4.67). Phenanthrene uptake was the least for cellulose and lignin, two major soil components. A comparison of phenanthrene Koc values and paraffinic carbon content revealed a positive correlation (Koc = 798 +/- 96.1 * paraffinic carbon (%), r2 = 0.56) and indicates that amorphous polymethylene carbon is an important consideration in phenanthrene sorption. This study establishes that aliphatic SOM domains have a strong affinity for phenanthrene and likely, other PAHs. Therefore, aliphatic structures, that are an important component of SOM, require more attention in the examination of sorption processes in terrestrial and sedimentary environments.

Adsorption↗

PubMed2002

High-resolution Fourier transform ion cyclotron resonance mass spectrometry of humic and fulvic acids: improvements and comparisons.

Full structural characterization of complex mixtures such as humic acid extracts has been elusive because of insufficient compound resolution with conventional techniques. Using electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry, we were able to resolve individual compounds within humic and fulvic acid mixtures (mass resolving power approximately 80000 at 300 m/z). We examined two samples in detail: (1) dissolved organic matter (primarily fulvic acids) from Suwannee River, GA, and (2) a humic acid extract from a degraded wood collected on Mt. Rainier, WA. Sample conditions (such as solvent, pH, and concentration) and instrument parameters (such as source voltages, trapping potentials, and excitation parameters) were optimized to yield the highest mass resolving power with the least mass discrimination in positive ion mode. High resolving power was achieved with low ion densities combined with coadding numerous scans. The increased resolution allowed molecular-level comparisons of the two samples which in turn could be used to estimate the relative similarity of individual compound distribution as well as an indication of the dominant diagenetic processes in the two source environments.

Benzopyrans↗

PubMedDate not supplied

Phenanthrene sorption to structurally modified humic acids.

Several studies emphasize the importance of soil organic matter characteristics in hydrophobic contaminant sorption and outline the strong dependence of sorption on organic matter aromaticity. In this study, the role of organic matter aromaticity in phenanthrene sorption was investigated using humic acids (HAs) from compost, peat, and soil that were structurally modified by bleaching, hydrolysis, oximation, and subcritical water extraction. The HAs were characterized with cross polarization magic angle spinning carbon-13 nuclear magnetic resonance (CPMAS 13C NMR) spectroscopy and used in batch equilibrations with phenanthrene. Bleaching substantially reduced the aromaticity of the samples whereas the other treatments increased the relative aromaticity. Phenanthrene sorption increased, even though there was a substantial reduction in sorbent aromaticity with some samples. The HAs that exhibited comparable CPMAS 13C NMR spectra and aromaticity did not behave similarly with respect to phenanthrene sorption. When the sorption data (K(oc) values) were correlated to sample aromaticity, the correlation coefficients (r2) did not exceed 0.39. Comparisons with the atomic H to C ratio provided slightly better r2 values (up to 0.54). This study demonstrates that macroscopic sorbent characteristics could not explain the observed phenanthrene sorption coefficients, aliphatic structural components of HAs can contribute appreciably to phenanthrene sorption, and organic matter physical conformation may regulate access to organic matter structures. Therefore, the use of only macroscopic sorbent properties, such as aromaticity, to predict and rationalize sorption values cannot solely be used to explain the behavior of organic contaminants in soil environments.

Adsorption↗

PubMedDate not supplied

Improvements in the two-dimensional nuclear magnetic resonance spectroscopy of humic substances.

Understanding pollutant sorption, bioremediation of these pollutants, and their interactions with humic substances requires knowledge of molecular-level processes. New developments with nuclear magnetic resonance (NMR) experiments and labeled compounds have improved the overall understanding of these mechanisms. The advancements made with two-dimensional NMR show great promise, as structural information and hydrogen-carbon bond connectivity can be discerned. This communication presents the application of improved two-dimensional NMR methods, the double quantum filtered (DQF) correlation spectroscopy (COSY) and echo/anti-echo heteronuclear single quantum coherence (HSQC) experiments, for use in structural studies of humic substances. Both experiments were found to produce significant improvements over the conventional COSY and heteronuclear multiple quantum coherence (HMQC) experiments that have been previously employed in similar studies. The more sensitive echo/anti-echo HSQC experiment produced more cross-peaks with higher resolution when compared with the HMQC spectra. The DQF-COSY significantly suppressed the diagonal signals and allowed numerous signals previously hidden in the standard COSY experiment to be observed. These improvements will aid current characterization strategies of humic substances from soils, sediments, and water and their subsequent reactions with pollutants and microorganisms.

Biodegradation, Environmental↗

PubMedDate not supplied

Solid-state carbon-13 nuclear magnetic resonance of humic acids at high magnetic field strengths.

Use of solid-state 13C nuclear magnetic resonance (NMR) spectroscopy has become commonplace in studies of humic substances in soils and sediments, but when modern high-field spectrometers are employed, care must be taken to ensure that the data obtained accurately reflect the chemical composition of these complex materials in environmental systems. In an effort to evaluate the quality of solid-state 13C NMR spectra obtained with modern high-field spectrometers, we conducted a series of experiments to examine spectra of various humic acids taken under a variety of conditions. We evaluate conditions for obtaining semiquantitative cross polarization magic angle spinning (CPMAS) 13C NMR spectra of humic acids at high magnetic field and spinning frequency. We examine the cross polarization (CP) dynamics under both traditional and ramp CP conditions on Cedar Creek humic acid. Fitted equilibrium intensities from these CP dynamic studies compare to within 3.4% of the intensities determined from a Bloch decay spectrum of the same sample. With a 1-ms contact time, ramp CP and traditional CP spectra were acquired on this sample and were found to compare to within 5.4% of the Bloch decay spectrum; however, the signal-to-noise ratio per hour of data acquisition was found to double under ramp CP conditions. These results demonstrate the power of applying modern solid-state NMR techniques at high magnetic field strengths. With these techniques, high-quality, semiquantitative spectra can be quickly produced, allowing the application of solid-state NMR techniques to more environmentally relevant samples, especially those where the quantity is limited.

Carbon Isotopes↗