This theses presents the synthesis and characterization of Cd(II)-, Pb(II)- and Hg(II)-aminoethanethiolates in aqueous media. 2-Aminoethanethiolate, a versatile sulfur andnitrogen (S/N) based ligand was used due to its resemblance to the naturally occurringamino acid, cysteine. The work is presented in four major parts: first, backgroundinformation on the versatile structural chemistry of Cd, Pb and Hg-thiolates with S/Ncontaining ligands; second, synthesis and characterization of Cd(II) with 2-aminoethanethiolates; third, synthesis and characterization and structural chemistry ofPb(II) with 2-aminoethanethiolates; and fourth, synthesis and characterization of Hg(II)-2-aminoethanethiolates in solution- and solid-state with emphasis on the mechanisticpathways for the formation of clusters.The compounds reported here are synthesized by direct addition of the metal saltsand the ligand in deionized water. For Cd(II)-thiolates, insoluble products (77 - 80 and 82- 84) due to the formation of oligomers and polymers were obtained. In Pb(II)-thiolates(85 - 89), the structural chemistry is variable due to the extensive array of coordinationenvironments Pb can acquire. This can be related to the stoichiometry of the reaction aswell as the reaction conditions. The structural trends in Cd(II)- and Pb(II)-thiolates arenot observed in the Hg(II)-thiolates. Rather the halide influences the formation ofmolecular as well as non-molecular structures. Systematic pathways for the formation ofthe compounds based on a variety of commonly observed structural 'building blocks' arepresented. For Cl, Br derivatives, a four-coordinate intermediate, [Hg(SR)2X2] (88 - 96)and for I derivatives three-coordinate intermediates, [HgI(SR)2] and [HgI2(SR)] (97 -100) can be considered as building units. The compounds were characterized withIR/Raman, NMR, MS, Uv-Vis and X-ray crystallography.

Biosorption is a phenomenon involving the mechanisms that basically mediate heavy metal tolerance of microorganisms as well as sequestration of heavy metals from environment. Different classes of microorganisms have different biosorption capacities, as a result of the differences in composition and types of functional groups found on cell surfaces. The present study was undertaken to identify the molecular mechanisms for lead [Pb(II)] biosorption in the white-rot fungus, Phanerochaete chrysosporium. The methodology involved selective blocking of the functional groups known to participate in heavy metal biosorption and allowed us to determine their relative roles in Pb (II) biosorption in this organism. The relative concentrations of the Pb (II) sorbed from the aqueous environment and Mg2+ and Ca2+ ions released to the aqueous environment were measured and compared with both native and chemically-modified biomasses by using atomic absorption spectroscopy. Fourier-Transform Infrared (FTIR) spectroscopy technique was used to monitor and analyze the molecular-level changes in both native and chemically modified cell surfaces upon Pb (II) exposure. Interactions of Pb (II) with the biomass surface was determined by observing the changes in wavenumber and absorbance of NH stretching and Amide I bands arising from the amine groups and C=O stretching band arising from the carboxyl groups. The roles of phosphate groups and lipids were also investigated. Carboxyl groups seemed to be the most important functional groups for Pb (II) biosorption in P. chrysosporium, since the biosorption capacity dramatically decreased (by 92.8 %) in carboxyl groups-blocked biomass. Amine groups were found to play a secondary and minor role in Pb (II) biosorption, only a slight decrease (6 %) in Pb (II) biosorption was detected with amine groups-blocked biomass. Blocking of phosphate groups provided a small increase in biosorptive capacity and did not appear to have much significant role in biosorption. Upon chemical treatment with acetone to extract lipids of the cell surfaces, an increase of 20.3 % in the Pb (II) biosorptive capacity was determined. It was concluded that carbonyl and carboxyl groups of chitin and glucan are the major sites and ion exchange via these groups is the main mechanism for Pb (II) biosorption in P. chrysosporium.

Made available in DSpace on 2016-06-02T20:36:20Z (GMT). No. of bitstreams: 1 1933.pdf: 2530807 bytes, checksum: a273b4240f1667021c251657e0a7623d (MD5) Previous issue date: 2007-07-27 / Financiadora de Estudos e Projetos / In this work, the removal of Pb(II) ions from simulated wastewaters, using a flow-through cell under galvanostatic condition was studied. With help of factorial design and response surface methodology, the variables current, electrolyte flow rate and the specific surface area of the three-dimensional cathode used (stainless-steel wool AISI 304) were simultaneously investigated in order to optimize the electrochemical system. Firstly, the specific surface area of the stainless-steel wool used as three-dimensional cathode was estimated. Then, factorial designs were employed on the study of the removal of Pb(II) ions for different values of cathodic current, electrolyte flow rate and mass of the stainless-steel wool (consequently, distinct specific surface areas). Finally, the response surface methodology for optimization of the removal process and the analysis of variance (ANOVA) for evaluation of the quality of the developed fitting models were employed. Higher values of removal efficiency (RE) were obtained for the highest values of cathodic current; RE values above 90% were obtained after 30 min electrolysis. Higher values of current efficiency (CE) (22%) were obtained for intermediate values of current (~ 0.24 A). For values of current in the range of 0.24 to 0.31 A, the CE values were lower, due to occurrence of simultaneous reactions such as reduction of oxygen, water and nitrate. Low CE values were also obtained for current values in the range of 014 A to 0.24 A as not all surface area of the steel wool was operating under mass transport control. The response surfaces developed for RE and CE values as a function of the current and flow rate revealed that the region close to 0.25 A and 250 L h-1 was the best for the removal of Pb(II) ions. In these conditions, the RE and CE values were 93 % and 22 %, respectively. Although the concentration of Pb(II) decreased from 54 mg L-1 to 0.39 mg L-1 after 90 min electrolysis, almost 99 % of removal of Pb(II) ions was achieved after only 40 min electrolysis. A mass-transfer coefficient (km) of 1.8 x 10-5 m s-1 was obtained for the electrochemical reactor. / Neste trabalho, foi estudado a remoção de íons Pb(II) de efluentes aquosos simulados, utilizando um reator eletroquímico flow-through operando em modo galvanostático. Com auxílio de planejamentos fatoriais e da metodologia de superfície de resposta (MSR), as variáveis corrente, fluxo de eletrólito e área superficial especifica do catodo tridimensional utilizado (esponja de aço inoxidável AISI 304) foram investigadas, simultaneamente, a fim de otimizar o sistema eletroquímico. Inicialmente, foi estimada a área superficial específica da esponja de aço inoxidável utilizada como catodo tridimensional. Em seguida, foram empregados planejamentos fatoriais no estudo da remoção de íons Pb(II) para diferentes valores de corrente catódica, fluxo de eletrólito e massa da esponja de aço (consequentemente, distintas áreas superficiais). Por último, foram empregadas a MSR para otimização do processo de remoção e a análise de variância (ANOVA) para avaliação da qualidade do ajuste dos modelos desenvolvidos. Maiores valores de eficiência de remoção (ER) foram obtidos para os maiores valores de corrente catódica; valores de ER acima de 90 % foram obtidos em 30 minutos de eletrólise. Maiores valores de eficiência de corrente (EC) (22 %) foram obtidos para valores intermediários de corrente (~ 0,24 A). Para valores de corrente na faixa de 0,24 A a 0,31 A, os valores de EC foram menores, devido à ocorrência de reações simultâneas tais como redução de oxigênio, água e nitrato. Baixos valores de EC também foram obtidos no intervalo de valores de corrente catódica de 014 A a 0,24 A, pois nem toda área superficial da esponja de aço estava operando sob controle de transporte de massa. As superfícies de resposta desenvolvidas para valores de ER e EC em função da corrente e fluxo de eletrólito revelaram que a região próxima de 0,25 A e 250 L h-1 foi a melhor para a remoção de íons Pb(II). Nestas condições, os valores de ER e EC foram 93 % e 22 %, respectivamente. Embora a concentração de íons Pb(II) diminuiu de 54 mg L-1 para 0,36 mg L-1 depois de 90 min de eletrólise, quase 99 % de remoção de íons Pb(II) foi alcançado após somente 40 min de eletrólise. Um coeficiente de transporte de massa (km) de 18,0 x 10-6 m s-1 foi obtido para o reator eletroquímico.

The concept of noncovalent bonding has evolved over the last number of years to include a very interesting class of interactions that is analogous to hydrogen bonding, called σ-hole interactions. These result from the depletion of electrostatic charge on the opposite end of a covalent bond between an electron-withdrawing substituent and a bond donor atom, which resides in groups 14-17 of the periodic table. One of these interactions is the tetrel bond (TB), whereby the bond donor is a group 14 element (T=C, Si, Ge, Sn, Pb). This thesis's primary goal is to explore the solid-state NMR parameters arising from the formation of tetrel bonds. To this end, combined density functional theory (DFT) and experimental multinuclear solid-state NMR spectroscopic investigations are carried out on complexes featuring carbon, Pb(II) and tin tetrel bonds. Firstly, solid-state NMR and computational approaches are used to examine a series of cocrystals formed from either caffeine or theophylline and several other small organic acceptor molecules. It is shown that the NMR response due to tetrel bond formation is detectible, but it can be hidden by other effects, including those of crystal packing. Careful analysis of NMR data alongside DFT calculations can reveal that the weak tetrel bond in these sorts of complexes increases the ¹³C chemical shift by 3-5 ppm. Next, a study of five Pb(II) centres hemidirectionally coordinated by isonicotinoyl hydrazone ligands demonstrates that the ²⁰⁷Pb NMR response is highly sensitive to the Pb(II) coordination environment. The NMR data indicate that a tetrel bond can induce an NMR response corresponding to a coordination environment between hemidirectional and holodirectional character. Finally, a series of organotin chloride donor molecules complexed with N-oxides and carboxylates, which feature short and linear tetrel bonds, are subjected to magic angle spinning (MAS) NMR experiments. The recorded data gives rise to a correlation between the tetrel bond length and both the experimental chemical shift and the ¹J(¹¹⁹Sn-³⁵Cl) coupling. Throughout this thesis, it is demonstrated that the isotropic chemical shift, the principal components of the chemical shift tensor, and indirect spin-spin coupling can be used to probe and gain insights into the electronic environment at the tetrel bond. More importantly, this work is fundamental to rationalize NMR data while refining crystal structure data in NMR crystallographic approaches for compounds featuring tetrel bonds.