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Biomedical subjects

M A Tarr

Publications and source records attributed to M A Tarr.

5 recordsLinked to original sources
PubMed2001

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.

Amino Acids↗
PubMed2001

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.

Indicators and Reagents↗
PubMed2000

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.

Humans↗
PubMed1999

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.

Benzopyrans↗