This work presents potentiometric investigations of [mycelium/metal ion/water] complex systems and the development of a new model investigating the ion-mycelium-fluid interactions. Since pH is a major parameter in soil ecology exhibiting large fluctuations, we proposed an improved equilibrium and also out-of-equilibrium potentiometric titration method in order to characterize the proton exchange behavior of the [mycelium/metal ion/water] system. Our model describes the dynamic relations and interactions within the soil complex subsystems consisting of fungal mycelium of Trametes hirsuta, water with or without metal ions (CuII and ZnII). Equilibrium modeling based on potentiometric titrations can be well described using four mycelium related components which are active in the pH range studied. In addition, our equilibrium calculations show clear differences with respect to metal-mycelium interactions: CuII interacts with acidic and basic deprotonable sites, while ZnII binds with neutral and basic deprotonable sites. Potentiometric out-of-equilibrium (i.e., perturbed pH) characterization suggests that important fungal heterogeneous complexity may act as definite proton pressure entities under continuously perturbed soil conditions. Raman micro-spectroscopy was also used to characterize the [mycelium/metal ion/water] complex systems. Our results demonstrate that potentiometry is a useful tool (intermediate technology) in studying biological complex matrices, facing pH perturbations, as well as their interactions with metal ions.

Two new synthetic melanin-like oligomers inspired by the synthesis of pheomelanin (cys-DOPA) were prepared using L-DOPA as a precursor and the amino acids serine (ser-DOPA) and threonine (thr-DOPA) for modifications. The products obtained exhibited appreciable antioxidant activity. The compounds were characterized by liquid chromatography-mass spectrometry (LC-MS), elemental analysis and infrared spectroscopy. The pKa values of the groups present in each melanin suspension were determined in aqueous solution by potentiometric and spectrophotometric titration. Cytotoxicity assays showed an IC50 > 500 mg L-1 resulting in non-toxic compounds for living cells. Finally, cys-DOPA, ser-DOPA and thr-DOPA exhibited antioxidant activity determined by the DPPH scavenging assay, with EC50 = 7.69, 1.02 and 27.60 mg L-1, respectively.

In this study the BEST7 software was employed to quantify different classes of functional groups and to model the proton titration behavior of humic substances. To illustrate the process, the Suwannee River fulvic acid of the IHSS (International Humic Substances Society) was used. Five categories - two classes of phenolic groups (phenol and cathecol), two classes of carboxylic groups (benzoic and phtalic) and the combination between them (salicylic) - of oxygenated groups were considered as being responsible for the potentiometric behavior of the sample and were quantitatively determined. The most and the least abundant groups were cathecol (3.300 ± 0.010 mmol g-1) and phenol (1.225 ± 0.070 mmol g-1), respectively. The estimated equilibrium constants were also determined and were in good agreement with the literature values for phenol and cathecol groups and for benzoic, phtalic and salicylic acids. Distribution diagrams of the species were generated with the software SPE and SPEPLOT.

Os estudos sobre enzimas têm mostrado que existe uma relação clara entre a evolução enzimática e a propriedade de promiscuidade catalítica que elas podem apresentar. Com isto, o desenvolvimento de sistemas biomiméticos capazes de atuar de modo promíscuo, de forma similar a algumas enzimas, mostrou-se um novo desafio para os químicos bioinorgânicos. Neste trabalho, reportamos a estrutura de raios X e os estudos em solução e de promiscuidade catalítica do complexo [(bpbpmp)FeIII(µ-OAc)2FeII](ClO4), (1), contendo o ligante binucleante não-simétrico 2-{[(2-hidroxibenzil)(2-piridilmetil)aminometil]-4-metil-6-[bis(2-piridilmetil)aminometil]}fenol (H2bpbpmp). Estudos de titulações potenciométrica e espectrofotométrica e cinéticos mostraram que esse composto de coordenação gera espécies ativas capazes de clivar o dsDNA (DNA de fita dupla) hidroliticamente, com um aumento de 1,9×10(8) na taxa de reação em comparação com a reação não catalisada, e capazes de oxidar o 3,5-di-terc-butilcatecol (3,5-dtbc), com k cat = 1,16 × 10-2 s-1 e K M = 7,1×10-4 mol L-1. Assim, o complexo 1 apresenta atividades de hidrolase e oxidoredutase, sendo um interessante modelo sintético para estudos de promiscuidade catalítica.

Catalytic promiscuity has emerged as an important property of many enzymes since the relationship of this property to enzymatic evolution became clear. Simultaneously, the development of suitable biomimetic catalytic systems capable of mimicking the promiscuous catalytic properties of such enzymes represents a new challenge for bioinorganic chemists. In this paper we report on the X-ray structure, the solution studies and the promiscuous catalytic activity of the mixed-valence complex [(bpbpmp)FeIII(µ-OAc)2FeII](ClO4), (1), containing the unsymmetrical dinucleating ligand 2-{[(2-hydroxybenzyl)(2-pyridylmethyl)aminomethyl]-4-methyl-6-[bis(2-pyridylmethyl)aminomethyl]}phenol (H2bpbpmp). Potentiometric and spectrophotometric titrations and kinetics studies showed that this coordination compound generates active species that promote hydrolytic cleavage of double strand DNA (dsDNA), with a rate enhancement of 1.9×10(8) over the non-catalyzed reaction, as well as promote oxidation of 3,5-di-tert-butylcatechol (3,5-dtbc), with k cat = 1.16 × 10-2 s-1 and K M = 7.1×10-4 mol L-1. Thus, complex 1 shows both hydrolase and oxidoreductase activities and can be regarded as a man-made model for studying catalytic promiscuity.

Os valores de acidez carboxílica (CA), fenólica (PhA) e total (TA) de um conjunto de cinco amostras padrão da Sociedade Internacional de Substâncias Húmicas (IHSS) e de quatro compostos modelo foram determinados pelo método de titulação potenciométrica. Os dados das curvas de titulação foram tratados pelo programa BEST7 assim como pela equação de Henderson-Hasselbalch modificada (MHHM) e os parâmetros obtidos mostraram-se extremamente dependentes do modelo matemático aplicado. Para as amostras de substâncias húmicas (SH), a aplicação da MHHM resultou em uma alta CA e uma baixa PhA, sendo o resultado praticamente oposto quando o programa BEST7 foi empregado. No caso dos compostos modelo entretanto, os valores de acidez convergiram aos valores esperados (teóricos) independente do modelo aplicado. Para investigar as razões das discrepâncias, variações na condução das titulações (p.e., titulação rápida ou lenta) também foram consideradas. O conjunto de informações mostrou que a determinação da acidez de SH por titulação potenciométrica é extremamente dependente do modelo matemático, assim como das condições experimentais aplicadas.

Carboxylic (CA), phenolic (PhA) and total (TA) acidity contents of five International Humic Substances Society (IHSS) standards and four model compounds were determined via the potentiometric titration method. Titration curves were scrutinized both by the BEST7 algorithm and the modified Henderson-Hasselbalch model (MHHM). In the case of IHSS samples, the fitting data depended on the analytical procedure undertaken. Whilst high CA and low PhA were usually recorded using the MHHM, the opposite trend was observed employing the BEST7 algorithm. In contrast, in the case of model compounds the acidity values matched well with theoretical data regardless of the procedure. In order to better understand the reasons for such discrepancies changes in the titrations procedure (e.g.: fast or slow) were also considered. General data strongly suggest that acidity determination of humic substances (HS) by potentiometric methods is extremely dependent on both the choice of mathematical model to fit experimental data points as well as the experimental conditions employed.

Estudos potenciométricos foram realizados para determinar o grau de ligação do ácido fítico com os íons Co(II) e o Mn(II), na ausência de dioxigênio. As constantes de equilíbrio para as principais espécies formadas são relatadas, e os resultados são representados na forma de diagramas de distribuição mostrando a concentração individual dos complexos como uma função do pH. Os valores das constantes de formação dos complexos foram elevados para as espécies em que o ligante encontra-se mais desprotonado. Os dados potenciométricos indicam que a espécie [MH4L]6-, encontra-se totalmente formada em pH 7,0 e a partir destes dados os complexos de Mn(II) e Co(II) com o ácido fítico foram sintetizados no estado sólido. Análises de infravermelho, termogravimetria e calorimetria exploratória diferencial foram utilizadas para caracterizar e investigar o comportamento térmico destes compostos. Os resultados conduziram a informações sobre composição, desidratação, estabilidade e decomposição térmica dos complexos.

Potentiometric studies were carried out to determine the binding degree of phytic acid with Co(II) and Mn(II) ions, in the absence of dioxygen. Equilibrium constants for all major complexes formed are reported, and the results are presented in the form of distribution diagrams showing the concentrations of individual complexes as a function of pH. The formation constants of the complexes show higher values for the species in which the ligand was more deprotonated. Potentiometric data indicates that the species [MH4L]6-, was totally formed at pH 7.0 and the complexes were synthesized from this data. A solid state complex of Mn(II) and Co(II) with phytic acid was synthesized. Thermogravimetry, differential scanning calorimetry, and infrared spectroscopy were used to investigate and characterize the thermal behavior of these compounds. The results led to information on the composition, dehydration, thermal stability and thermal decomposition of the isolated complexes.

Este trabalho avaliou o comportamento do agente encapsulante beta -ciclodextrina ( beta-CD) adicionado ao leite de cabra submetido ao processo de desidratação por "spray-dryer", através de análise termogravimétrica e de cromatografia gasosa. Após a desidratação, a amostra adicionada de beta-CD apresentou um rendimento real de 10,59% com taxa de perda de 0,04% (em relação ao valor teórico esperado 10,6% ); enquanto na amostra sem adição do agente encapsulante o rendimento real foi de 9,57%, com taxa de perda de 4,27% (valor teórico esperado 10% ). Através da análise termogravimétrica (TGA), verificou-se que são volatilizados 44% e 21% dos ácidos comerciais C8 e C10 , respectivamente. Os resultados cromatográficos mostraram uma perda de aproximadamente 30% dos ácidos C8 e 20% dos ácidos C10 , nas amostras de leite de cabra sem beta -CD em relação às amostras com beta-CD. Tais porcentagens estão de acordo com os valores estimados para os ácidos comerciais. Com base nos parâmetros estudados, podemos inferir que há menor perda dos ácidos graxos C8 e C10 na amostra de leite de cabra com beta-CD, provavelmente devido ao efeito encapsulante, aumentando a estabilidade térmica dos ácidos.

This work evaluated the effect of the encapsulant agent beta-cyclodextrin (beta-CD) added the goat milk submitted to the "spray-dryer" dehydration process, through thermogravimetric analysis and gas cromatography. After dehydration, the sample added of beta-CD presented a real yield of 10,59%, with a loss rate of 0,04% (in relation to the expected theoretical value 10,6%); while in the sample without addition of the encapsulant agent the real yield was 9,57%, with a loss rate of 4,27% (expected theoretical value 10% ). It was verified that the volatilization of 44% and 21% of the commercial acids C8 and C10 , respectively, through the thermogravimetric analysis (TGA). The cromatographic results showed losses of approximately 30% of the C8 acids and 20% of the C10 acids, in samples of goat milk without beta-CD, in relation to the samples with beta-CD. These percentages corroborate the values estimated for commercial acids. On the basis of these studied parameters, we can infer that there is a minor loss of the fatty acids C8 and C10 in the sample of goat milk with beta-CD, probably due to the encapsulant effect, which increase the thermal stability of the acids.

From the leaves of Bauhinia forficata kaempferol and four flavonoid glycosides, 3,7-di-O-alpha-L-rhamnopyranosylkaempferol, 3,7-di-O-alpha-L-rhamnopyranosylquercetin, 3-O-[alpha-L-rhamnopyranosyl-(1->6)-beta-D-glucopyranosyl]-7-O-alpha-L-rhamnopyranosylkaempferol and 3-O-[alpha-L-rhamnopyranosyl-(1->6)-beta-D-glucopyranosyl]-7-O-alpha-L-rhamnopyranosylquercetin were obtained. From the flowers only the flavonoid 7-O-alpha-L-rhamnopyranosylkaempferol was isolated. The structures were established by chemical and spectroscopic methods.

Galactomananas podem ser empregadas como aditivos na indústria alimentícea para modificar a viscosidade do produto final. Como não são absorvidas pelo organismo humano, sua adição a alimentos dietéticos é muito promissora. Os equilíbrios entre Fe(III) e galactomananas e arabinogalactana de várias leguminosas foram caracterizadas por titulações potenciométricas e espectroscopia de EPR. Os logaritmos das constantes de equilíbrio para a formação dos complexos ML (M = Fe(III) e L = unidade monomérica dos biopolímeros) foram iguais a 15,4, 14,1 e 18,5 para as galactomananas de C. fastuosa, L. leucocephala e S. macranthera, respectivamente. Os valores de log K para a formação das espécies protonadas (MHL) foram 3,1, 3,3 para as galactomananas de C. fastuosa, L. leucocephala e não foi detectado no caso da galactomanana de S. macranthera. Os valores de log de K para a formação de ML2 foram 14,1, 13,3 e 15,2, respectivamente. Não foi possível obter dados relativos ao equilíbrio entre arabinogalactana e Fe(III) devido à formação de produtos insolúveis logo no início das titulações. Os ensaios no estado sólido mostraram não somente uma grande interação dipolar entre dois íons Fe(III) na estrutura polimérica complexada, tanto maior quanto menos substituída é a galactomanana, mas também a estabilidade térmica resultante desta complexação. Os produtos complexados podem conferir uma abrangência maior na utilização em produtos dietéticos, pois a presença de um metal essencial no complexo, quando de sua descomplexação nos vários processos fisiológicos dos organismos, faculta a absorção desse íon metálico.

Galactomannans can be employed in food industries to modify the final rheological properties of the products. Since they are not absorbed by the living organisms they can also be used in dietary foods. The equilibria involving the interactions of Fe(III) and galactomannans and arabinogalactan of several leguminous plants were characterized by potentiometric titrations and EPR spectroscopy. The log of the equilibrium constants for the formation of ML species, where M is the metal ion and L is the monomeric unit of the biopolymers, were 15.4, 14.1 and 18.5, for the galactomannans of C. fastuosa, L. leucocephala and S. macranthera, respectively. Log K values for protonated species (MHL) were 3.1, 3.3, and were not detected for the galactomannan of S. macranthera. The log K values for the formation of ML2 were 14.1, 13.3 and 15.2, respectively. Early formation of insoluble products in the equilibrium with arabinogalactan and Fe(III) prevented acquisition of reliable data. The solid complexes assays showed a great dipolar interaction between two Fe(III) ions in the inner structure of the biopolymer which increased as the degree of substitution of the galactomannan decreased, and also showed the resulting thermal stability. The complexes impart a new possibility of providing essential metal ions in dietary foods since decomplexation of the complexes can occur at different pH values existing in the human body.

A necessidade de se estudar compostos modelo é a de se compreender como os sítios de quelação de substâncias orgânicas complexas como os ácidos húmicos e nitro-húmicos atuam frente a um íon metálico, pois as substâncias húmicas são potenciais fertilizantes orgânicos. As propriedades químicas principais dos complexos encontrados entre os ácidos 3-nitroftálico e 4-nitroftálico e os íons metálicos Fe(III) e Zn(II) foram estudadas por titulações potenciométricas, espectroscopia ultravioleta-visível e voltametria cíclica, e uma titulação potenciométrica experimental foi feita com uma mistura de modelos de ácidos nitro-húmicos e Cu(II). Calculou-se as constantes de equilíbrio para os sistemas, cujas espécies foram detectadas pelas outras técnicas empregadas. Estudos comparativos entre sítios de quelação derivados de nitrossalicilatos e nitrocatecolatos com Fe(III), Zn(II) e Cu(II) são apresentados. Neste trabalho, os ácidos nitro-húmicos, além de possuírem maior teor de nitrogênio que os ácidos húmicos, também exibiram a vantagem de que alguns centros de quelação, preferencialmente, se ligam a íons metálicos nos valores de p[H] próximos aos valores normais do solo, 7,0 a 7,5.

The study of model compounds is necessary in order to obtain information about complex organic substances as in the case of humic substances (HS). These substances are potential organic fertilizers and have other important functions in soils, natural waters and organic sediments. The main chemical properties of the complexes formed from 3-nitrophthalic and 4-nitrophthalic acids and the metal ions Fe(III) and Zn(II) were studied using potentiometric titrations, ultraviolet-visible spectroscopy (UV-Vis) and cyclic voltammetry (CV). A trial potentiometric titration was done with a mixture of the models for nitrohumic acids and Cu(II). Equilibrium constants for the systems were calculated and UV-Vis and CV were employed to monitor the formation of the species. Comparative studies involving chelating centres of nitrosalicylic acids and nitrocatechols with Fe(III), Zn(II) and Cu(II) are presented. The initial studies involving the nitrohumic substances (NHS), a laboratory artifact of HS have been made and good evidence was found for the further use of NHS as a potential organic fertilizer as well as HS. In this present work one of the observed advantages of NHS over HS was that some aromatic nitro- centres can bind some metal ions at p[H] values of normal soils, near 7.0 to 7.5.

Brometo, sulfato, selenito e selenato foram encontrados formando pontes na cavidade dos complexos mononucleares e binucleares de Obisdien:Zn(II) e Obisdien:Mg(II) em solução aquosa a 25 °C e m = 0,100 M (KCl). Medidas de equilíbrio potenciométrico foram realizadas para determinar as constantes de formação das espécies formadas nestes sistemas na faixa de pH de 2 a 12. Para os complexos do Obisdien:Zn(II): ânions, foram detectadas quatro espécies com o íon brometo, cinco espécies com o íon sulfato, seis espécies com o íon selenito e quatro espécies com o íon selenato. Os complexos binucleares hidróxidos predominam sobre todas as outras espécies e a constante de associação diminui na seqüência: SeO4(2-) > SeO3²> SO4(2-) > Br-. O sistema envolvendo os complexos de Obisdien:Mg(II) apresenta três espécies com o íon brometo, quatro espécies com o íon sulfato, cinco espécies com o íon selenito e cinco com o íon selenato. A variação da constante de associação para este sistema é o mesmo observado no sistema anterior: SeO4(2-) > SeO3² > SO4(2-) > Br-. Cálculos de mecânica molecular mostram que os complexos de Obisdien dizinco(II) e dimagnésio(II) adotam várias conformações de baixa energia com diferentes separações Zn-Zn e Mg-Mg permitindo a coordenação dos ânions SeO4(2-), SeO3(2-), SO4(2-), Br- e OH-.

Bromide, sulfate, selenite and selenate were found to form bridges in the cavity of mononuclear and binuclear Obisdien:Zn(II) and Obisdien:Mg(II) complexes in aqueous solution at 25.0 °C and m = 0.100 M (KCl). Potentiometric equilibrium measurements were used to determine the formation constants of the species formed in these systems in the pH range 2-12. For the Obisdien: Zn2+:anions complexes, we have established the existence of four species for bromide ion, five species for sulfate ion, six species for selenite ion and four species for selenate ion. We found that the hydroxo binuclear complexes predominate over the others species, and the binding strength decreases in the sequence: SeO4(2-) > SeO3(2-) > SO4(2-) > Br-. The Obisdien:Mg(II) system presents three species in case of binding with bromide ion, four with sulfate ion, five with selenite ion and five with selenate ion. Variation of the binding strength in the Obisdien:Mg(II) complexes is the same as in the Obisdien:Zn(II) complexes: SeO4(2-) > SeO3(2-) > SO4(2-) > Br-. Molecular mechanics calculations show that the dizinc(II)- and dimagnesium(II)-Obisdien complexes adopt several low energy conformations differing in their Zn to Zn and Mg to Mg separations that allow the coordination of SeO4(2-), SeO3(2-), SO4(2-), Br- and OH- anions.