Thermodynamic Characterization of Humic Acid-surfactant Interaction: New Insights into the Characteristics and Structure of Humic Acids

ABSTRACT Humic acids (HA) are a component of humic substances (HS), which are found in nearly all soils, sediments, and waters. They play a key role in many, if not most, chemical and physical properties in their environment. Despite the importance of HA, their high complexity makes them a poorly understood system. Therefore, understanding the physicochemical properties and interactions of HA is crucial for determining their fundamental role and obtaining structural details. Cationic surfactants are known to interact electrostatically and hydrophobically with HA. Because they are a very well-known and characterized system, they offer a good choice as molecular probes for studying HA. The objective of this study was to evaluate the interaction between cationic surfactants and HA through isothermal titration calorimetry in a thermodynamic manner, aiming to obtain information about the basic structure of HA, the nature of this interaction, and if HA from different origins show different basic structures. Contrary to what the supramolecular model asserts, HA structure is not loosely held, though it may separate depending on the conditions the HA are subjected to in their milieu. It did not show any division or conformational change when interacting with surfactants. The basic structure of the HA remains virtually the same regardless of the different sources and compositions of these HA.

DNA-lipid systems: A physical chemistry study

It is well known that the interaction of polyelectrolytes with oppositely charged surfactants leads to an associative phase separation; however, the phase behavior of DNA and oppositely charged surfactants is more strongly associative than observed in other systems. A precipitate is formed with very low amounts of surfactant and DNA. DNA compaction is a general phenomenon in the presence of multivalent ions and positively charged surfaces; because of the high charge density there are strong attractive ion correlation effects. Techniques like phase diagram determinations, fluorescence microscopy, and ellipsometry were used to study these systems. The interaction between DNA and catanionic mixtures (i.e., mixtures of cationic and anionic surfactants) was also investigated. We observed that DNA compacts and adsorbs onto the surface of positively charged vesicles, and that the addition of an anionic surfactant can release DNA back into solution from a compact globular complex between DNA and the cationic surfactant. Finally, DNA interactions with polycations, chitosans with different chain lengths, were studied by fluorescence microscopy, in vivo transfection assays and cryogenic transmission electron microscopy. The general conclusion is that a chitosan effective in promoting compaction is also efficient in transfection.

Interaction between cationic and conventional nonionic surfactants in the mixed micelle and monolayer formed in aqueous medium

Mixed micellization and surface properties of cationic and nonionic surfactants dimethyl decyl-, tetradecyl- and hexadecyl phosphineoxide mixtures are studied using conductivity and surface tension measurements. The models of Rubingh, Rosen, and Clint, are used to obtain the interaction parameter, minimum area per molecule, mixed micelle composition, free energies of mixing and activity coefficients. The micellar mole fractions were always higher than ideal values indicating high contributions of cationics in mixed micelles. Activity coefficients were less than unity indicating synergism in micelles. The negative free energies of mixing showed the stability of the surfactants in the mixed micelles.

Síntese e caracterização de argilas organofílicas contendo diferentes teores do surfactante catiônico brometo de hexadeciltrimetilamônio

The major applications of organoclays are in adsorption of organic polluents. The objective of this work was the synthesis and characterization of organoclays using differents amounts of cationic surfactant hexadecyltrimethylammonium bromide. The clays were characterized by low angle x-ray diffraction (XRD), scanning electron microscope (SEM), infrared with Fourier tranformation (FTIR), BET surface area, elemental analysis (CHN), Foster swell and adsorption of methylene blue. The surfactant can adsorb in differents forms in the interlamelar region changed the basal spacing. The presence of the surfactant adsorbed can be favorable or not in adsorption of the methylene blue due the different interactions dye-organoclays.

Decomposição térmica de complexos de Zn e Cd com isomaleonitriladitiolato (imnt)

Thermal decomposition of [Bu4N]2[Zn(imnt)2] and [M(NH3)2(imnt)] complexes with M = Zn and Cd, and imnt = (bis 1,1-dicyanoethylene-2,2 dithiolate) in inert atmosphere was investigated by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). Pyrolysis studies at different temperatures, 300, 400, 500, and 600 ºC, in N2 atmosphere were performed and the products were characterized by X-ray diffraction (XRD), infrared and Raman spectroscopy, and scanning electron microscopy (SEM). The products were identified as sulfide sub-micron particles, along with amorphous carbon. Particle sizes estimated by SEM were ca. 50 nm for the cationic complexes and 500 nm for the neutral complexes.

SYNTHESIS AND CHARACTERIZATION OF HDTMA-ORGANOCLAYS: INSIGHTS INTO THEIR STRUCTURAL PROPERTIES

This study aims to synthesize and characterize organoclays developed from an Argentinian montmorillonite (Bent) using hexadecyltrimethylammonium bromide (HDTMA-Br) as the intercalation agent. Subsequently, an adsorption mechanism is proposed. The obtained organoclays were more hydrophobic than the starting clay. Surfactant molecules were adsorbed initially through cation exchange in sites placed in the interlayer space of the clay. Adsorption in such sites continued until the interlayer space was saturated. Depending on the surfactant loading introduced during the intercalation process, different organizations of surfactant in the interlayer were obtained. Further adsorption of surfactant occurred in the mesopores generated by tactoids in the "house of cards" organization. This process kept surfactant molecules relatively free and out of the interlayer space.

Análise TG-ROC de testes de imunofluorescência no diagnóstico de leishmaniose visceral canina

OBJETIVO: Analisar a acurácia do diagnóstico de dois protocolos de imunofluorescência indireta para leishmaniose visceral canina. MÉTODOS: Cães provenientes de inquérito soroepidemiológico realizado em área endêmica nos municípios de Araçatuba e de Andradina, na região noroeste do estado de São Paulo, em 2003, e área não endêmica da região metropolitana de São Paulo, foram utilizados para avaliar comparativamente dois protocolos da reação de imunofluorescência indireta (RIFI) para leishmaniose: um utilizando antígeno heterólogo Leishmania major (RIFI-BM) e outro utilizando antígeno homólogo Leishmania chagasi (RIFI-CH). Para estimar acurácia utilizou-se a análise two-graph receiver operating characteristic (TG-ROC). A análise TG-ROC comparou as leituras da diluição 1:20 do antígeno homólogo (RIFI-CH), consideradas como teste referência, com as diluições da RIFI-BM (antígeno heterólogo). RESULTADOS: A diluição 1:20 do teste RIFI-CH apresentou o melhor coeficiente de contingência (0,755) e a maior força de associação entre as duas variáveis estudadas (qui-quadrado=124,3), sendo considerada a diluição-referência do teste nas comparações com as diferentes diluições do teste RIFI-BM. Os melhores resultados do RIFI-BM foram obtidos na diluição 1:40, com melhor coeficiente de contingência (0,680) e maior força de associação (qui-quadrado=80,8). Com a mudança do ponto de corte sugerido nesta análise para a diluição 1:40 da RIFI-BM, o valor do parâmetro especificidade aumentou de 57,5% para 97,7%, embora a diluição 1:80 tivesse apresentado a melhor estimativa para sensibilidade (80,2%) com o novo ponto de corte. CONCLUSÕES: A análise TG-ROC pode fornecer importantes informações sobre os testes de diagnósticos, além de apresentar sugestões sobre pontos de cortes que podem melhorar as estimativas de sensibilidade e especificidade do teste, e avaliá-los a luz do melhor custo-benefício.

Cistatina C, PCR, Log TG/HDLc e Sindrome Metabolica estao Relacionados a Microalbuminuria na Hipertensao

Fundamento: Em pacientes com hipertensão arterial sistêmica, a microalbuminúria é um marcador de lesão endotelial e está associada a um risco aumentado de doença cardiovascular. Objetivo: O objetivo do presente estudo foi determinar os fatores que influenciam a ocorrência de microalbumiúria em pacientes hipertensos com creatinina sérica menor que 1,5 mg/dL. Métodos: Foram incluídos no estudo 133 pacientes brasileiros atendidos em um ambulatório multidisciplinar para hipertensos. Pacientes com creatinina sérica maior do que 1,5 mg/dL e aqueles com diabete mellitus foram excluídos do estudo. A pressão arterial sistólica e diastólica foi aferida. O índice de massa corporal (IMC) e a taxa de filtração glomerular estimada pela fórmula CKD-EPI foram calculados. Em um estudo transversal, creatinina, cistatina C, colesterol total, HDL colesterol, LDL colesterol, triglicerídeos, proteína C-reativa (PCR) e glicose foram mensurados em amostra de sangue. A microalbuminúria foi determinada na urina colhida em 24 horas. Os hipertensos foram classificados pela presença de um ou mais critérios para síndrome metabólica. Resultados: Em análise de regressão múltipla, os níveis séricos de cistatina C, PCR, o índice aterogênico log TG/HDLc e a presença de três ou mais critérios para síndrome metabólica foram positivamente correlacionados com a microalbuminuria (r2: 0,277; p < 0,05). Conclusão: Cistatina C, PCR, log TG/HDLc e presença de três ou mais critérios para síndrome metabólica, independentemente da creatinina sérica, foram associados com a microalbuminúria, um marcador precoce de lesão renal e de risco cardiovascular em pacientes com hipertensão arterial essencial.

Estudo cinético por TG e DSC da decomposição térmica de alguns adutos de haletos de cádmio

By DSC data, the kinetical parameters Ea , n and A were calculated for the thermal decomposition of the adducts CdCl2.2dmf, CdCl2.dmf and CdBr2.dmf (dmf= dimethylformamide) by using Rogers and Smith method. The found values were : Ea = 85, 176 and 101 kJ mol-1 , n= 0.23, 0.25, and 0.17, A= 2.40x10(9), 1.89x10(19) and 1.07x10(9) respectively. By TGA data, the kinetical patameters for the thermal decomposition of the adduct CdCl2.1,5 dmeu (dmeu=dimethylethyleneurea) were calculated by using five different methods.

Estimating the value of the metal-ligand bond dissociation enthalpy<D> (M-L) for adducts using empirical equations supported by TG data

In this work is presented and tested (for 106 adducts, mainly of the zinc group halides) two empirical equations supported in TG data to estimate the value of the metal-ligand bond dissociation enthalpy for adducts: <D> (M-O) = t i / g if t i < 420 K and <D> (M-O) = (t i / g ) - 7,75 . 10-2 . t i if t i > 420 K. In this empirical equations, t i is the thermodynamic temperature of the beginning of the thermal decomposition of the adduct, as determined by thermogravimetry, andg is a constant factor that is function of the metal halide considered and of the number of ligands, but is not dependant of the ligand itself. To half of the tested adducts the difference between experimental and calculated values was less than 5%. To about 80% of the tested adducts, the difference between the experimental (calorimetric) and the calculated (using the proposed equations) values are less than 15%.

Calcium phosphate biomaterials from marine algae. Hydrothermal synthesis and characterisation

Calcium phosphate compounds such as Hydroxyapatite (HAp) were prepared by hydrothermal synthesis with phycogenic CaCO3 as starting material. Material obtained was characterised by usual methods (XRD, FTIR, TG, N2-adsorption, SEM and EDX) in order to study its physical-chemical characteristics. The prepared HAp showed that it may be suitable for use as a biomaterial.

Comportamento térmico do 8-quinolinol e seus nitro-derivados

The compounds 5-nitro-8-quinolinol and 5,7-dinitro-8-quinolinol were obtained by nitration of the chelant 8-quinolinol. The compounds were characterized through EA, MNR, XRD, IR, TG, DTA and DSC. It was verified through thermal analysis that the compounds show consecutive processes of sublimation, fusion and vaporization. During the vaporization process, partial thermal decomposition was observed, with formation of carbonaceous residues. Considering a slower heating rate, the sublimation is the prevalent process to the nitro-derivatives while the vaporization is the main process to 8-quinolinol. The thermal stability follows the decreasing order from 5,7-dinitro-8-quinolinol to 5-nitro-8-quinolinol to 8-quinolinol.

Pilarização de uma argila brasileira com poliidroxications de alumínio: preparação, caracterização e propriedades catalíticas

Montmorillonite clay from Brazil was pillared with aluminium polyhydroxications. The influence of aging of the pillaring solution and the concentration of the clay suspension on the properties of the prepared materials was studied. The materials were characterized by chemical analysis, XRD and pore analysis by N2 adsorption. The catalytic properties were evaluated in the cumene cracking reaction. Results showed that the pillarization process increases the basal spaces of natural clay from 9.7 to 18.5 Å and the surface area from 41 to 300 m²/g.

Estudo da síntese da zeólita ZSM-5 a partir de argilas naturais

The synthesis of ZSM-5 zeolite was studied by three synthesis methods: standard synthesis, three day synthesis and synthesis employing clays (kaolin and montmorillonite). The raw materials and prepared materials were characterized by Chemical Analysis by X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD). The results show that it is possible to synthesized ZSM-5 zeolite using clays as raw materials. Kaolin gives phases of higher crystalinity than montmorillonite.