Call number: LD2668 .T4 1979 B57 / Master of Science

Copies of author's previously published works inserted. Bibliography: leaves 260-299. This thesis describes the concept of organic matter turnover and various methods to measure the decay rates of organic materials in the soil. Methods are developed to separate SOM from different locations within the soil matrix. Free particulate organic matter (POM), located between or outside the soil aggregates is isolated. Occluded POM is disaggregeted by sonification. The compositional differences noted among the three components of SOM are used to describe the changes that OM undergoes during decomposition. The process is followed as organic matter enters the soil, is enveloped in aggregates and is eventually incorporated into the microbial biomass and metabolites then becoming associated with clay minerals.

Copies of author's previously published works inserted. / Bibliography: leaves 260-299. / xxii, 299 leaves, [7] leaves of plates : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis describes the concept of organic matter turnover and various methods to measure the decay rates of organic materials in the soil. Methods are developed to separate SOM from different locations within the soil matrix. Free particulate organic matter (POM), located between or outside the soil aggregates is isolated. Occluded POM is disaggregeted by sonification. The compositional differences noted among the three components of SOM are used to describe the changes that OM undergoes during decomposition. The process is followed as organic matter enters the soil, is enveloped in aggregates and is eventually incorporated into the microbial biomass and metabolites then becoming associated with clay minerals. / Thesis (Ph.D.)--University of Adelaide, Dept. of Soil Science, 1997

Made available in DSpace on 2015-04-22T22:01:57Z (GMT). No. of bitstreams: 1 Wamber Boni de Souza.pdf: 2659314 bytes, checksum: 7f9a2f165e36496d3cc87db36897ea3e (MD5) Previous issue date: 2013-06-03 / Fundação de Amparo à Pesquisa do Estado do Amazonas / This work describes the mercury and a summary on toxicity of organomercury, as well as environmental importance of the HS, addressing structural aspects of the interaction between carboxylic groups from humic and fulvic acids and Hg, in two reviews. A third review is presented the Density Functional Theory (DFT) applied to theoretical study of mercury and its compounds. Environmental chemistry of Hg is extensively revised, especially the reduction process Hg2+  Hg+  Hg0. The Hg can also be found in forms organomercury, which the methylmercury (methyl-Hg, CH3Hg+) and dimethylmercury (dimethyl-Hg, CH3(Hg)2) are the most important. Structurally, the difference between the two forms of Hg is the number of methyl groups. Important tool in the consolidation of experimental data, theoretical calculations have proven that they are capable of complementing experimental results. The DFT B3LYP functional with LANL2DZ basis set are performed for the neutral structures dimethylmercury (Dimetil-Hg), methylmercury (MetHgCl), methylmercury bromide (MetHgBr), methylmercury iodide (MetHgI) and charged methylmercury (Met-Hg), methylmercury oxide ion (MetHgO-), methylmercury sulfide ion (METHgS-), methylmercury selenide ion (MetHgSe-). Additionally, the interaction of the Model of Humic Substance Molecules (MHSM) (Benzoic acid (AB), Phthalic acid (AFT), Salicylic acid (AS) e 2,4-dihydroxybenzoic acid (2,4-ADHBC) and carboxylic groups from fulvic acid (AFRS) structure proposed for the Suwannee River with Hg2+ has been investigated theoretically by using DFT method with high level B3LYP/ LANL2DZ model in order to contribute to the understanding of the behavior of Hg in nature. Findings show that the structure of methyl-Hg is more stable and less reactive than dimethyl-Hg. The bond lengths C-Hg on Met-Hg-X (X = Cl-, Br- and I-) increase with increasing volume. In the case of Met-Hg-X (X = O2-, S2- and Se2-), the bond length C-Hg remains virtually unchanged. The charge distribution analysis has revealed that the Hg oxidation tendency to reduce or anion depending on what is on. The trend of reduction/oxidation is accompanied by a greater stabilization energy (NBO) and ΔEL. The HUMO-LUMO orbital shows the structures Met-Hg-X (X = Cl-, Br- and I-) that has a larger Δε Met-Hg-X (X = O2-, S2- and Se2-). Finally, the use of B3LYP/LANL2DZ shows errors in bond length in relation to the experimental data varying between 4.74 and 6.43%. The results showed that the interaction between the carboxylic acid and Hg2+ ions indicate the occurrence of a reduction process rather than complexation in the MMSH. The interaction AB Hg ions formed with the carboxylic AB proved to be the most stable among all the MMSH-Hg. The highest values of stabilization energy of second order were observed by the molecules AB Hg e AFT Hg. Findings showed that the complexation and reduction depends on the location of the carboxyl groups in the structure of fulvic acid in the AFRS. Furthermore, the binding energy, geometry and energy gap is altered by interaction with the carboxylic groups of AFRS with Hg2+. / Esta tese descreve o mercúrio e um resumo sobre a toxicidade dos compostos organomercuriais, bem como a importância ambiental da SH, abordando aspectos estruturais da interação entre grupos carboxílicos dos ácidos húmicos e fúlvicos e Hg, em duas revisões. A terceira revisão é apresentada a Teoria do Funcional da Densidade (DFT) aplicada ao estudo teórico de mercúrio e seus compostos. A química ambiental do Hg é revista extensivamente, especialmente o processo de redução do Hg2+  Hg+  Hg0. O Hg pode ser encontrado também em formas organomercurais, das quais o metilmercúrio (metil-Hg, CH3Hg+) e dimetil-Hg (dimetil-Hg CH3(Hg)2) são as mais importantes. Estruturalmente a diferença entre as duas formas de Hg é a quantidade de grupos metilas. Ferramenta importante na consolidação de dados experimentais, os cálculos teóricos já comprovaram que são capazes de complementar resultados experimentais. A DFT e o funcional B3LYP com o conjunto de base LANL2DZ foram usados para a otimizações de geometria para as estruturas neutras dimetilmercúrio (Dimetil-Hg), cloreto de metilmercúrio (MetHgCl), brometo de metilmercúrio (MetHgBr), Iodeto de metilmercúrio (MetHgI) e carregadas metilmercúrio (Met-Hg), íon óxido de metilmercúrio(MetHgO-), íon sulfeto de metilmercúrio (METHgS-) e íon seleneto de metilmercúrio (MetHgSe-). Além disso, a interação dos grupos carboxílicos de moléculas modelos de substâncias húmicas (MMSH), (Ácido benzoico (AB), Ácido ftálico (AFT), ácido salicílico (AS) e ácido 2,4-diidroxibenzocarboxílico) e de ácido fúlvico (AFRS) de estrutura proposta do rio Suwannee com Hg2+ foi investigado teoricamente por DFT no nível de cálculos B3LYP/LANL2DZ, a fim de contribuir para o entendimento do comportamento do mercúrio na natureza. Os resultados mostram que a estrutura do metil-Hg é mais reativa e menos estável que a estrutura do dimetil-Hg. Os comprimentos de ligação C Hg no Met-Hg-X (X = Cl-, Br- e I-) aumentam com o aumento do volume. No caso do Met-Hg-X- (X = O2-, S2- e Se2-) o comprimento de ligação C Hg permanece praticamente inalterado. A análise de distribuição de carga revelou que o Hg apresenta tendência para redução ou oxidação dependendo do ânion que está ligado. A tendência de redução/oxidação é acompanhada por uma maior energia de estabilização (NBO) e ΔEL. Os orbitais HOMO-LUMO mostram que as estruturas Met-Hg-X (X = Cl-, Br- e I-) possuem maior Δε que Met-Hg-X- (X = O2-, S2- e Se2- ). Finalmente o uso do B3LYP/LANL2DZ apresentou erros nos comprimento de ligação em relação aos dados experimentais variando entre 4,74 e 6,43%. Para as MMSH os resultados mostraram de modo geral, que a interação entre os íons carboxílicos e Hg2+ indicam a ocorrência de um processo de redução ao invés de complexação. Entre todas as MMSH-Hg, a interação AB Hg formada com os íons carboxílicos da AB mostrou ser a mais estável. As moléculas AB Hg e AFT Hg possuem os maiores valores de energia de estabilização de segunda ordem. Especificamente para os AFRS, os resultados indicam que a complexação e redução dependem da localização dos grupos carboxílicos na estrutura de ácido fúlvico. Além disso, a energia de ligação, a geometria

The Suwannee River natural organic matter (SRNOM) was fractionated by preparative size-exclusion chromatography (SEC) into seven molecular weight (MW) fractions. The SRNOM and its MW fractions were subsequently analyzed for their concentrations of acidic functional groups by direct titrations, average MWs and MW distributions by semi-analytical SEC, and charge-to-MW distributions by capillary electrophoresis. Carboxyl concentrations in the MW fractions were inversely proportional to their average MWs. Conversely, the phenolic concentrations, though smaller than the carboxyl concentrations, were proportional to average MWs. Hysteresisthe non-overlap between sequential forward and reverse titrationswas observed for the SRNOM and its MW fractions, where the reverse titrations predicted a greater concentration of carboxylic acid groups than the forward titration. Because hysteresis is thought to be caused by the base-catalyzed hydrolysis of esters, this suggests that ester groups in the SRNOM are distributed over all MWs. Data for direct titrations, MW distributions, and capillary electrophoresis were evaluated by a computational scheme that solves for the most probable distribution of acidic functional groups and charges on solutes in the SRNOM and the MW fractions as a function of pH. Depending on the MW ranges of the samples, solutes in the SRNOM and the MW fractions are predicted to have from one to a maximum of 25 carboxyl groups per solute. Most phenolic groups are predicted to be on solutes that have a minimum of two carboxyl groups. At low pH, all samples have high relative abundances of solutes with the lowest charges. The charges of solutes are predicted to increase with increasing pH due to the sequential ionization of acidic functional groups. Depending on the MW ranges of the samples, the maximum probable charges of solutes in the SRNOM and the fractions at high pH are -12 to -30. By knowing the most probable distribution of charge and abundances of acidic functional groups, researchers will make better estimates of thermodynamic parameters and models that describe equilibria between metals and natural organic matter in the environment.