The contamination of groundwater by arsenic is currently a major concern in Bangladesh. Arsenic in groundwater was first detected in 1993 following reports of many people suffering from arsenical diseases. Further investigations showed the extent of the problem with large areas of the country's water supply being affected and millions of people at serious risk of arsenic poisoning. Technology for arsenic removal from water already exists. However, the socioeconomic conditions which prevail in Bangladesh, do not permit implementation of this type of technology on grounds of cost. The main objective of this study was to develop a low cost technique for the removal of arsenic from contaminated groundwater using the naturally occurring iron, which is another water quality constraint in Bangladesh. The approach was to form arsenic-iron complexes by coprecipitation and adsorption of arsenic on iron. It has been demonstrated that provided the iron levels are sufficiently high (say >_ 1.2 mg/1), simple shaking of a container and allowing the arsenic-iron complex to settle out for 3 days could reduce the concentration of arsenic from 0.10 mg/l to Bangladesh standard (0.05 mg/1). In experimental program, As(III) form of arsenic was used as this form is more likely to be present in groundwater. From laboratory studies, it was shown that the removal rate was largely controlled by the Fe/As ratio, pH and the As concentration. Arsenic removal increases with increasing Fe/As ratio and is favoured by increasing pH in the range of 5 to 8. Separation of the precipitates was achieved by settlement. Following prolonged settlement, it was found that arsenic removal could exceed the removal achieved by filtration through a 0.45 μm filter paper. The experiments demonstrated that about 77% arsenic removal could be achieved from water containing 0.2 mg/l As(III), 4.0 mg/1 Fe at pH 7.5 by manual flocculation (1 min manual mixing) and 3 days settlement. The use of ordinary charcoal, which is cheap and easily available, was investigated for removal of arsenic and was found to be ineffective. From maps of the known distributions of As, Fe and pH, it was evident that 63% of the area in Bangladesh complied with the Bangladesh standard for arsenic. By interpreting the maps and applying the potential removal by coprecipitation-adsorption and settlement technique, it was estimated that a further 8% of area would comply with the Bangladesh standard freeing an additional 7 million people from arsenic contamination.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1976. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

No description available.

<p> A number of complexes FeX2Ln (X = Cl, Br; L = formamide, N-methylformamide, N,N-dimethylformamide, acetamide, benzamide, isobutyramide, urea, N-methylurea, N,N'-dimethylurea, thioacetamide, thiourea, N-methylthiourea, N,N'-dimethylthiourea, benzothiazole, aniline) have been prepared and investigated by means of Mossbauer and infrared spectroscopy and magnetic measurements. It has been possible to distinguish firstly between 4-coordinate and 6-coordinate complexes and secondly between a number of different types of 6-coordinate complexes.</p> / Thesis / Master of Science (MSc)

No description available.

This thesis describes the synthesis of a host of polynuclear iron complexes synthesised with phenolic oxime ligands, fundamentally developing the coordination chemistry of iron with these ligands. The metallic cores that occur within iron phenolic oxime clusters were found to contain almost exclusively oxo-centred triangles and oxo-centred tetrahedra. We found that we could alter the reaction conditions or derivatise the ligands and develop these basic building blocks into more elaborate arrays, exerting a degree of control over creating larger or smaller clusters. Chapter one describes the syntheses, structures and magnetic properties of new iron complexes alongside previously synthesised related complexes (4, 5, 8, 9 and 15) containing salicylaldoxime (saoH2) or derivatised salicylaldoximes (RsaoH2). These are [Fe3O(OMe)(Ph-sao)2Cl2(py)3]·2MeOH (1·2MeOH), [Fe3O(OMe)(Ph-sao)2Br2(py)3]·Et2O (2·Et2O), [Fe4(Ph-sao)4F4(py)4]·1.5MeOH (3·1.5MeOH), [Fe6O2(OH)2(Et-sao)2(Et-saoH)2(O2CPh)6] (4), [HNEt3]2[Fe6O2(OH)2(Et-sao)4(O2CPh(Me)2)6]·2MeCN (5·2MeCN), [Fe6O2(O2CPh)10(3-tBut-5-NO2-sao)2(H2O)2]·2MeCN (6·2MeCN), [Fe6O2(O2CCH2Ph)10(3-tBut-sao)2(H2O)2]·5MeCN (7·5MeCN), {[Fe6Na3O(OH)4(Me-sao)6(OMe)3(H2O)3(MeOH)6]·MeOH}n (8·MeOH) and [HNEt3]2[Fe12Na4O2(OH)8(sao)12(OMe)6(MeOH)10] (9). The predominant building block appears to be the triangular [Fe3O(R-sao)3]+ species which can self-assemble into more elaborate arrays depending on reaction conditions. The four hexanuclear and two octanuclear complexes of formulae [Fe8O2(OMe)4(Mesao) 6Br4(py)4]·2Et2O·MeOH (10·2Et2O·MeOH), [Fe8O2(OMe)3.85(N3)4.15(Mesao) 6(py)2] (11), [Fe6O2(O2CPh-4-NO2)4(Me-sao)2(OMe)4Cl2(py)2] (12), [Fe6O2(O2CPh-4-NO2)4(Et-sao)2(OMe)4Cl2(py)2]·2Et2O·MeOH (13·2Et2O·MeOH), [HNEt3]2[Fe6O2(Me-sao)4(SO4)2(OMe)4(MeOH)2] (14) and [HNEt3]2[Fe6O2(Etsao) 4(SO4)2(OMe)4(MeOH)2] (15) all are built from series of edge-sharing [Fe4( μ4- O)]10+ tetrahedra. Complexes 10 and 11 display a new μ4-coordination mode of the oxime ligand and join a small group of Fe-phenolic oxime complexes with nuclearity greater than six. Chapter three then introduces co-ligands to the reaction scheme to compete with the salicylaldoxime ligands for metal coordination sites. Five tetranuclear and two nononuclear complexes are stabilised with salicylaldoxime (saoH2) or derivatised salicylaldoximes (R-saoH2) in conjunction with either 1,4,7- triazocyclononane (tacn), 2-hydroxymethyl pyridine (hmpH) or 2,6-pyridine dimethanol (pdmH2), [Fe4O2(sao)4(tacn)2]·2MeOH (16·MeOH), [Fe4O2(Mesao) 4(tacn)2]·2MeCN (17·2MeCN), [Fe4O2(Et-sao)4(tacn)2]·MeOH (18·MeOH), [Fe9NaO4(Et-sao)6(hmp)8]·3MeCN·Et2O (19·3MeCN·Et2O), [Fe4 (Etsao) 4(hmp)4]·Et-saoH2 (20·Et-saoH2), [Fe4(Ph-sao)4(hmp)4]·2MeCN (21·2MeCN) [Fe9O3(sao)(pdm)6(N3)7(H2O)] (22). Chapter four straps two salicylaldoxime units together in the 3-position, using ligands with aliphatic a,W-aminomethyl links, allowing the assembly of the polynuclear complexes [Fe7O2(OH)6(H2L1)3(py)6](BF4)5·6H2O·14MeOH (23·6H2O·14MeOH), [Fe6O(OH)7(H2L2)3][(BF4)3]·4H2O·9MeOH (24·4H2O·9MeOH) and [Mn6O2(OH)2(H2L1)3(py)4(MeCN)2](BF4)5(NO3)·3MeCN·H2O·5py (25·3MeCN·H2O·5py). In each case the metallic skeleton of the cluster is based on a trigonal prism in which two [MIII 3O] triangles are tethered together via three helically twisted double-headed oximes. The latter are present as H2L2- in which the oximic and phenolic O-atoms are deprotonated and the amino N-atoms protonated, with the oxime moieties bridging across the edges of the metal triangles. Both the identity of the metal ion and the length of the straps connecting the salicylaldoxime units have a major impact on the nuclearity and topology of the resultant cage, with, perhaps counter-intuitively, the longer straps producing the “smallest” clusters.

No description available.

The synthesis of diiron thiolate complexes was carried out using two ligands that were expected to furnish improved catalytic activity, solubility in water, and stability to the metal complexes. The water-soluble phosphine 1,3,5-triaza-7- phosphaadamantane, PTA, coordinates to the Fe centers forming the disubstituted complex (m-pdt)[Fe(CO)2PTA]2, which presents one PTA in each iron in a transoid arrangement. Substitution of one CO ligand in the (m-pdt)[Fe(CO)3]2 parent complex forms the asymmetric (m-pdt)[Fe(CO)3][Fe(CO)2PTA]. Enhanced water solubility was achieved through reactions with electrophiles, H+ and CH3 +, which reacted with the N on the PTA ligand forming the protonated and methylated derivatives, respectively. The 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), IMes, was reacted with (m-pdt)[Fe(CO)3]2 yielding the asymmetric (m-pdt)[Fe(CO)3][Fe(CO)2IMes], an electron rich, air stable complex that does not show reactivity with H+. Electrocatalytic production of hydrogen was studied for the all-CO, bis-PMe3, mono- and di-PTA FeIFeI complexes, as well as the PTA-protonated and -methylated derivatives. The all-CO species produce H2, in the presence of the weak HOAc, at their second reduction event, FeIFe0 ?? Fe0Fe0, that occurs at ca. ??1.9 V, through an EECC mechanism. The mono- and di-substituted phosphine complexes present electrocatalytic production of H2 from the Fe0FeI redox state; this reduction takes place at ??1.54 V for (m-pdt)[Fe(CO)3][Fe(CO)2PTA], and at ca. ??1.8 for the disubstituted PMe3 and PTA derivatives. A positive charge on the starting complex does not have an effect on the production of H2. It was found that the protonated and methylated derivatives are not the catalytic species for H2 production. At their first reduction event the neutral precursor forms, and catalysis occurs from the FeIFeI complex in all cases. The possibility of enhanced catalytic activity in the presence of H2 O was explored by conducting electrochemical experiments in the mixed CH3CN:H2O solvent system for the PTA-substituted complexes. The reduction potential of the catalytic peak is shifted to more positive values by the presence of H2 O. The cyclic voltammogram of {(m-pdt)[Fe(CO)2(PTA?? H)]2}2+ in CH3CN:H2O 3:1 shows the reduction of a more easily reduced species in the return scan. This curve-crossing event provides evidence for the (h2-H2)FeII intermediate proposed in the ECCE mechanism.

No description available.

[pt] Tiossemicarbazonas e seus complexos metálicos apresentam um amplo espectro de atividades biológicas. As tiossemicarbazonas α(N)-heterocíclicas tem sido muito estudadas em razão de sua comprovada ação antitumoral. O mecanismo de ação antitumoral dessas drogas se dá pela inibição da enzima ribonucleotídeo difosfato redutase (RDR), que catalisa o ciclo de reações redox envolvido na conversão de ribonucleotídeos a desoxirribonucleotídeos durante a síntese do ADN. A forma ativa dessas drogas é o complexo de ferro. Desse modo, a obtenção de novos complexos de Fe de tiossemicarbazonas α(N)-heterocíclicas constitui uma importante estratégia para a obtenção de candidatos a antitumorais. Nesse trabalho investimos no estudo, em solução aquosa, da interação entre 2- piridinoformamida tiossemicarbazona (H2Am4DH) e seus derivados N(4)-metil (H2Am4M), N(4)-etil (H2Am4E) e N(4)- fenil (H2Am4Ph) e os íons Cu(II) e Fe(III). Esse estudo foi monitorado por espectroscopia de absorção na região do UV-vis. Para o cálculo das constantes de formação dos complexos foram levados em consideração os valores das constantes cumulativas calculadas inicialmente para as tiossemicarbazonas livres ( β HL e β H2L+). Quatro novos complexos de Fe(III) foram isolados e caracterizados: [Fe(2Am4DH)2]Cl, [Fe(2Am4Me)2]Cl, [Fe(2Am4Et)2]Cl e [Fe (2Am4Ph)Cl3]. Os valores de susceptibilidade magnética para os complexos estão na faixa de 1,36-1,66 MB. Esses valores são próximos do calculado (1,73 MB) para complexos de Fe(III), octaédricos, spin baixo. Os dados de infravermelho indicam que as tiossemicarbazonas estão coordenadas ao ferro através do sistema quelante Npy-N-S. O comportamento eletroquímico dos complexos é bastante similar, sugerindo que suas estruturas em solução são igualmente similares. A toxicidade das tiossemicarbazonas e de seus complexos de ferro frente à Artemia salina foi estudada como um pré-screening para sua ação antitumoral. Os valores de LD50 obtidos indicam que esses compostos têm atividade citotóxica, sugerindo que poderiam igualmente apresentar ação antitumoral. Além disso, os potenciais de redução FeIII/FeII observados para os complexos estão dentro da faixa ideal dos redutores celulares. Assim, se confirmada a atividade antitumoral o mecanismo de ação poderia envolver a redução FeIII/FeII por tiois celulares, como sugerido para outros complexos de ferro de tiossemicarbazonas. / [en] Thiosemicarbazones and their metal complexes present a wide range of bioactivities. It has been shown that the antitumoral action of á(N)-heterocyclic thiosemicarbazones occurs through the inhibition of ribonucleotide diphosphate reductase (RDR), a key enzyme involved in the conversion of ribonucleotides into deoxyribonucleotides during DNA syntheses. The active form of the drugs are their iron complexes. Hence the preparation of new iron complexes with á(N)- heterocyclic thiosemicarbazones constitutes an interesting strategy in designing antitumoral drug candidates. In the present work the interactions of 2- pyridineformamide thiosemicarbazone (H2Am4DH) and its N(4)- methyl (H2Am4Me), N(4)-ethyl (H2Am4Et) and N(4)-phenyl (H2Am4Ph) derivatives with Cu(II) as well as Fe(III) ions in aqueous solution were studied, monitored in the visible region by the variations of the absorption spectrum. The cumulative protonation constants â HL and â H2L+ were determined for the ligands by a potentiometric method and were used in the calculation of the complex formation constants. The iron(III) complexes [Fe(2Am4DH)2]Cl, [Fe (2Am4Me)2]Cl, [Fe(2Am4Et)2]Cl and [Fe(2Am4Ph)Cl3] were obtained and characterized. The values of magnetic moments in the 1.59-1.66 BM range are close to the calculated value of 1.73 BM, characteristic of the presence of one unpaired electron as in low spin iron(III) complexes. The infrared data for the complexes indicate coordination of the thiosemicarbazones through the Npy-N-S chelating system. The resemblance of electrochemical behaviors suggests that the structures of the complexes in solution are also very similar. The toxicity of the thiosemicarbazones and their metal complexes against Artemia salina was assayed as a prescreening of antitumoral action. The low values of LD50 obtained for the studied compounds in this assay indicate that they could present antineoplastic properties. Moreover, the determined values of FeIII/FeII redox potentials for the complexes fall in the range of cellular reductants. Therefore, if the complexes present antitumoral activity, their biochemical pathway could involve FeIII/FeII reduction by cellular thiols, as suggested previously for iron complexes of other thiosemicarbazones.