Mechanistic study on the solubility enhancement of puerarin by coamorphous technology / 药学学报

Puerarin (PUE), as an isoflavone component, has a wide range of pharmacological activities, while its poorly aqueous solubility limits the development of solid oral dosage forms. In this study, PUE along with nicotinamide (NIC) were prepared into the coamorphous system by solvent-evaporation method and characterized by powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR). In addition, its dissolution behavior and solubilization mechanism were also investigated. PUE-NIC coamorphous was a single homogeneous binary system, with a single glass transition temperature at 35.1 ℃. In comparison to crystalline PUE, during the dissolution process, coamorphous PUE-NIC not only exhibited the "liquid-liquid phase separation" (LLPS) phenomenon, but the formation of Ap type complexation (1∶1 and 1∶2) between PUE and NIC molecules was also verified, which significantly improved the solubility of PUE and prolonged the supersaturation time, and would benefit its absorption.

A new strategy based on acid-alkali complexation for rapidly and accurately fishing phytochemicals in sennae folium / 中草药·英文版

Objective: There are some anthraquinones, anthraquinones and flavonones in Sennae Folium which exhibited significant acidity, such as sennoside A/B and sennoside C/D. The current strategies used in separating these components are mainly based on conventional column chromatography which is time consuming, laborious and costly. This study is aimed at exploring a method of precipitation extraction of acid components in Sennae Folium. Using alkaloid as a “hook”, it is reasonable to use the principle of “acid-alkali complexation” to "fish" the acidic components in Sennae Folium. Methods: Isothermal titration calorimeter (ITC) was used to measure the extraction efficiency of different alkaloids. Then, alkaloid determined by ITC was mixed with extracting solution of Sennae Folium to form complex. High performance liquid chromatography coupled with mass spectrometry (HPLC-MS2) was used to investigate the ingredients “fished” by berberine (Ber). The mechanism of “fishing” process was explained by ITC, optical activity, fluorescence spectrometry and scanning electron microscope. Results: The ITC results proved that the choice of “hook” was particularly important in the process of “fishing”. Among the hooks, the fishing efficiency of the isoquinoline alkaloids (Ber) was the highest, reaching 10.3%. Nine ingredients were detected and determined by HPLC-MS2, and the main components were sennoside A/B and sennoside C/D. Based on ITC test of Ber and sennoside A, the combination mechanism of the two ingredients was a chemical reaction with a nearly binding ratio (2:1). Fluorescence and optical properties of the active ingredients were changed after complexation. By scanning electron microscope, we found that two types of components had obviously self-assembled behavior during the formation process. Conclusion: Ber successfully “fished” the main acidic components, sennoside A/B and sennoside C/D, from Sennae Folium. Combined with different characterizations, the “fishing” process was determined as a chemical association reaction induced by electrostatic interaction or π-π stacking. Therefore, with special identification ability, the “fishing” process had the potential of practical application.

Preparation technology of liquiritin based on ultrafiltration-complexation extraction and back extraction technology / 中草药

Objective To establish a complexation extraction and back extraction technology for the separation and purification of liquiritin from Glycyrrhiza uralensis ultrafiltrate. Methods Taking the extraction rate of liquiritin as an index, the optimum composition of complexing extractant was first determined by uniform design, and then orthogonal experiments were used to optimize the conditions of complexing extraction. Taking the back extraction rate of liquiritin as an index, the process conditions for the back extraction of liquiritin were determined by investigating the type and concentration of back extractant. Results The complexation extraction research found that the complexing extractant should be a binary complexing extractant composed of trialkyl phosphine oxide (TRPO) and sulfonated kerosene. The optimum extraction conditions for liquiritin were as follows: TRPO-sulfonated kerosene (9∶91), pH value of G. uralensis ultrafiltrate was adjusted to 4, volume ratio of organic phase to aqueous phase was 1∶1, and average extraction rate of liquiritin reached 99.6%. The study of back extraction process showed that under the condition that the volume ratio of organic phase to back extractant was 1∶1, 17.5 mmol/L NaOH aqueous solution was the best back extractant, and the back extraction rate of liquiritin was 99.3%. Conclusion Under the optimized conditions, the liquiritin in G. uralensis ultrafiltrate can smoothly transfer from the ultrafiltrate to the complexing extractant and then to the alkaline back extractant. The total transfer rate of liquiritin is as high as 98.9%. This paper can provide a new preparation technology for the separation and purification of liquiritin.

Preparation technology of glycyrrhizin acid based on ultrafiltration- complexation extraction technology / 中草药

Objective: To establish a technique for preparing glycyrrhizin acid (GA) by ultrafiltration-complexation extraction. Methods The effect of pH on the extraction rate of GA from ultrafiltrate was investigated in the range of 4-8; The orthogonal test was used to optimize the technological conditions for complexation extraction of GA; The extraction conditions of GA were determined by investigating the type and concentration of the extractant. Results The optimum extraction conditions for GA were as follows: pH value of Glycyrrhiza uralensis ultrafiltrate was adjusted to 2, TRPO-sulfonated kerosene (5:95, volume percent), volume ratio of organic phase to aqueous phase was 1:1, and average extraction rate of GA reached 99.2%. The best back extraction conditions for GA were as follows: 22.5 mmol/L NaOH aqueous solution was used as the stripping agent, the volume ratio of organic phase to stripping agent was 1:1, the single back extraction rate of GA reached 98.8%, and the total transfer rate of GA was 98.1%. Conclusion Ultrafiltration-complexation extraction technology can be used as a new process for the preparation of GA.

Box-Behnken response surface method optimized technological research of ultrafiltration-complexation extraction and back extraction technology to prepare liquiritigenin / 中草药

Objective: A technological route was established for preparing liquiritigenin from the licorice ultrafiltrate. Methods: U5(53) uniform design was used to optimize the ultrafiltration process with the retention rate of liquiritigenin as the index; Box-Behnken response surface method was used to optimize the complexation extraction process with the extraction rate of liquiritigenin as the index; The technological condition of back extraction of liquiritigenin was determined by the liquiritigenin stripping rate. Results: The optimal ultrafiltration conditions for liquiritigenin were inorganic ceramic membranes with a pore size of 10 nm, a pressure of 0.12 MPa, and solution temperature of 25 ℃, retention rate of liquiritigenin was 98.74%. Optimum complexation extraction conditions were as following: 1% TRPO complexing agent, extraction for 10 min in 5 mL organic phase solution, the extraction rate of liquiritigenin was 99.44%; The 12.5 mmol/L NaOH aqueous solution was the best back-extractant, and the back extraction rate was 98.88%. Conclusion: As a new Chinese medicine extraction technology, ultrafiltration-complexation extraction and back extraction technology have the advantages of high selectivity, high efficiency, and recycling of extractant, which can provide a new preparation technology for the research of liquiritigenin.

Complexation and enhancement of temozolomide solubility with cyclodextrins

ABSTRACT Temozolomide is a poorly soluble anti-cancer drug used in the treatment of some brain cancers. Following literature reports about the enhancement of solubility and stability for these kinds of drugs upon complexation with cyclodextrins, we aimed to form an inclusion complex between temozolomide and the different types of cyclodextrins (CDs) to enhance its solubility. In this study, three different cyclodextrins (ß -CD, hydroxyl-ß-CD and γ-CD) were used, and changes in solubility was measured by UV-Vis Spectroscopy and HPLC. Morphological changes upon complexation were shown by the Scanning Electron Microscope (SEM), and weight loss profiles with respect to temperatures which were unique to the compounds were shown by Thermogravimetric Analysis. Changes in heat release profiles were shown by Differential Scanning Calorimeter (DSC). Drug solubility was measured to be increased to around 25% for 1:1 molar ratio for all used CD complexations. Changes of morphology, heat release and weight loss profiles are consistent with the formation of an inclusion complex between CDs and temozolomide. In this study, success was shown in the enhancement of temozolomide solubility upon complexation with different types of CDs. It has been demonstrated that cyclodextrins can be used as complexing agents for poorly soluble anti-cancer drugs, increasing their solubility and hence drug availability

Study on chemical constituents of self-settling from Huanglian Jiedu Decoction and effects on PC12 induced by CoCl2 / 中草药

Objective To optimize the preparation conditions of precipitation from Huanglian Jiedu Decoction (HJD). The main components of precipitation content were measured and the protective effect of compound precipitation on injured PC12 cell was evaluated. Methods The preparation process of precipitation was determined by time and water supply; Contents of baicalin, berberine, geniposide, palmatine, coptis, and wogonoside were determined by HPLC. The effect of HJD was evaluated and the precipitation on neurotoxic PC12 cells were injured by CoCl2 with CCK-8 assay. Results Under the condition (extracted by refluxing for 30 min using the amount of water which was 10 times of the quality of herbs), the quality of dry precipitation was about 10% of mass of the supernatant, and 81% of the precipitation were organic acids and alkaloids, baicalin was 42.12%, berberine was 31.17%, coptis was 5.89%, wogonoside was 1.50%, palmatine was 0.60%, and geniposide was not detected. EC50 of supernatant and precipitation on injured PC12 was 28.25 μg/mL and 19.58 μg/mL, respectively. Conclusion The preparation process of precipitation is simple and reproducible, and this study reveals that the compound precipitation from HJD is mainly composed of acid-alkali complex. Compared with the supernatant, the compound precipitation shows better neuroprotective activity, and provides basic data for the secondary development of HJD.

Thermodynamic studies of naringenin-isonicotinamide cocrystals / 药学学报

The purpose of this study was to investigate the thermodynamics of naringenin (NAR)-isonicotinamide (INT) cocrystal (stoichiometric ratio, 1∶2) formed in different solvents. The dissolution behavior of cocrystal was explored in the water. Solubility of NAR-INT cocrystals under various temperatures were measured, followed by fitting the complexation model to calculate the thermodynamic parameters solubility products (Ksp), complexation constants (K12) and Gibbs energy change (ΔG) of cocrystal during formation progress. Ternary phase diagrams (TPDs) of the NAR-INT-solvent systems under various temperatures were plotted. Based on the non-linear simulation, 1∶2 complexation model was well fitted to the NAR-INT cocrystal formation in ethanol, isopropanol and ethyl acetate, while no complexation model was more suitable for that in methanol. The cocrystallization reaction was exothermic and spontaneous (ΔG H S Ksp increased while K12 decreased when increasing temperature, suggesting that the two components could cocrystallize more easily at the lower temperature. In comparison to TPDs in other solvents, the area of homogeneous liquid phase in ethyl acetate was the smallest, indicating the easiest formation of NAR-INT cocrystal in ethyl acetate. The current study provides a theoretical foundation for preparation and optimization of scale-up NAR-INT cocrystals.

Biological functions of SPA-PEI conjugate as one key component for construction of a novel antibody-targeted DNA delivery system / 重庆医学

Objective To investigate the biological function of SPA-PEI conjugate(staphylococcal protein A-polyethyleneimine cross-linker),which is one key component for construction of a novel antibody-targeted DNA delivery system.Methods The binding capacity of SPA-PEI conjugate with multiple sources of IgG was determined by enzyme-linked immunosorbent assay and neutralization inhibition assay.The binding capacity of SPA-PEI conjugate with DNA fragment was determined by DNA gel retardation assay,and its DNA condensing ability was measured by Ethidium bromide exclusion assay.Results SPA-PEI conjugate could bind well to many species-derived IgGs.SPA-PEI conjugate had no significant effect on the binding properties of SPA.SPAPEI conjugate could neutralize negative charges of the plasmid DNA or DzTi.Its DNA condensing ability was nearly same to that of free PEI,which suggested a excellent DNA condensing ability of the SPA-PEI conjugate.Conclusion SPA-PEI cross-linkers prepared by this project group maintained the biological activity of SPA and PEI.SPA-PEI cross-linkers could be used for the construction of a novel antibody-targeted non-virus DNA delivery system.

Study on Binding Characteristics of Aminocarboxyl Chelating Ligands for Metal Ions / 分析化学

The feasibility of frontal chromatography for determining the complexation stability constant KML and total mole of binding site Λo was demonstrated by the accuracy and precision binding experiments between metal ions (Cu2+, Ni2+ and Co2+) and chelating ligand (IDA), in which R2>0.98 and RSD Asp>Glu;binding strength of metal ions for chelate ligands followed Cu2+>Ni2+>Co2+;and the binding effect with NaAc-HAc buffer was the best.In aqueous solution, quantum computing of binding energy (ΔE) and gibbs free energy (ΔG) between chelating ligand and metal ion was performed at the M06/6-311++G (d, p) level.According to ΔE and ΔG, the binding rules between chelating ligand and metal ion were predicted theoretically.These rules were basically in agreement with above experimental results.The present work provided effective method for studying on binding characteristics of metal ions for aminocarboxyl chelating ligands, thus exhibited a good foundation for improving the stability of immobilized metal affinity chromatographic column and solving the leakage of metal ions from the column in the process of competitive elution.

Impact analysis of inclusion complexation on micromeritic properties and dissolution behavior of carvedilol.

The study aimed at investigating an inclusion complexation technique to improve solubility and dissolution characteristics of carvedilol by successful complexation with β-cyclodextrin. Inclusion complexes (ICs) of drug and β-cyclodextrin were prepared by kneading method in four different ratios. Physical mixtures were also prepared in identical ratios to compare the efficacy of prepared ICs. The preparations were subjected to rheological studies, drug loading, in vitro release study, FT-IR spectroscopy, thermal events analysis by DSC, X-ray diffraction, scanning electron microscopy (SEM) and accelerated stability study. IC granules were free flowing and compressible. FT-IR study denoted to absence of any chemical interactions between drug and carrier. DSC and X-ray diffraction suggested the presence of crystalline drug in the complexes. Dissolution of ICs revealed significant enhancement of release rate and extent compared to untreated drug. MDT, %DE and T25%, T50% and T80% indicated marked improvement in release rate from complexes. Kinetic modeling suggested that fickian diffusion was the predominant mechanism of drug release from solid complexes. Stability samples showed no significant alterations in DSC and FT-IR studies that referred to the stability of ICs. ICs were compatible, effective and stable over time. Further studies can be planned to investigate their therapeutic efficacy.

Insoluble drug delivery strategies: review of recent advances and business prospects

The emerging trends in the combinatorial chemistry and drug design have led to the development of drug candidates with greater lipophilicity, high molecular weight and poor water solubility. Majority of the failures in new drug development have been attributed to poor water solubility of the drug. Issues associated with poor solubility can lead to low bioavailability resulting in suboptimal drug delivery. About 40% of drugs with market approval and nearly 90% of molecules in the discovery pipeline are poorly water-soluble. With the advent of various insoluble drug delivery technologies, the challenge to formulate poorly water soluble drugs could be achieved. Numerous drugs associated with poor solubility and low bioavailabilities have been formulated into successful drug products. Several marketed drugs were reformulated to improve efficacy, safety and patient compliance. In order to gain marketing exclusivity and patent protection for such products, revitalization of poorly soluble drugs using insoluble drug delivery technologies have been successfully adopted by many pharmaceutical companies. This review covers the recent advances in the field of insoluble drug delivery and business prospects.

Thermodynamics of baicalein-nicotinamide co-crystallization process / 中国药科大学学报

Baicalein-nicotinamide(BE-NCT)co-crystal was chosen as model drug to investigate the thermody-namic characteristics.Solubilities of BE in NCT solutions in ethyl acetate at different temperatures were deter-mined in order to explain the complexation behavior of BE-NCT co-crystal.Thermodynamic parameters of co-crys-tal formation progress were calculated.Ternary phase diagrams (TPDs)of the BE-NCT-ethyl acetate systems at various temperatures were established.The non-linear fitting equation according to 1 ∶1 complexation mechanism of BE-NCT co-crystal demonstrated a good correlation between calculated and experimental data (R2 >0.98). Co-crystal formation is a spontaneous process(ΔG°<0).Increase in temperature resulted in the increase of Ksp;decrease of K11 and a narrowed co-crystal zone.The degree of spontaneous reaction also decreased with increased temperature.The spontaneous reaction no longer carried out if the temperature reached T* =315 K sinceΔG°=0(ΔH°=-6.314 ×10 -2 kJ/mol;ΔS°=-0.200 5 J/mol.K).A drop in temperature favors the complexation between BE and NCT in ethyl acetate.Since NCT has higher solubility than BE in ethyl acetate;the TPDs of co-crystal was asymmetric.The DSC diagrams of products prepared via three presupposed methods confirmed that the BE-NCT co-crystal could be generated in solutions of nonstoichiometric compositions.

Characteristics, Complexation and Analytical Methods of Darunavir.

What is it? Darunavir is a protease inhibitor used in the treatment of HIV infection. It is an important drug of therapy cocktail for patients infected with the virus. On the market there are darunavir ethanolate tablets of 75, 150, 300, 400, 600 and 800mg, because this is the most stable form. It is commercialized by Janssen-Cilag with the name PrezistaTM. Why we started? This drug has low water solubility and poor bioavailability, therefore requires administration in doses relatively high to the success of the therapeutic effect. The complexation of drugs by using cyclodextrin is welcome in this respect to improve the solubility and hence increase the dissolution rate of poorly soluble drugs. A monograph about this compound has not been described, thus it is an extremely important quality control of darunavir to demonstrate its effectiveness and safety. What we did? Some existing analytical techniques have been discussed in this manuscript, focusing on bioanalytical and pharmaceutical quality control applications. What we found? This review showed the published analytical methods reported for the determination of darunavir and discuss about its characteristics and complexation with cyclodextrin.

Development of Buccal Patches for Delivery of Darifenacin from Beta-Cyclodextrin Complexes / Development of Buccal Patches for Delivery of Darifenacin from Beta-Cyclodextrin Complexes

Drug-cyclodextrin complexes improve aqueous solubilityand dissolution rate of poorly water-soluble drugs.Solubilisation followed by buccal delivery of poorlywater-soluble drugs can be advantageous for increasingdrug absorption. Darifenacin is an antispasmodic usedagainst urinary incontinence and specifically blocksM3 muscarinic acetylcholine receptors in smoothmuscle. M3 receptors are mainly located in exocrineglands, smooth muscle and vascular endothelium. Theoral absorption of darifenacin is poor owing to its lowsolubility. It also has poor bioavailability (15-19%) dueto a high rate of first-pass metabolism. Complexationwith beta-cyclodextrin was carried out to enhancesolubility. The best results were obtained by co-grindingin a 1:1 molar ratio of drug: ?-cyclodextrin. The solidinclusion complexes were characterized by DSC, X-raydiffractometry and FTIR. Inclusion complexes showedhigher dissolution rates than the pure drug. Controlledreleasemucoadhesive patches were prepared with twohydroxypropyl methylcellulose (HPMC) polymers,K100M CR and K15. The patches were assessed forsurface pH, folding endurance, swelling, mucoadhesiveproperties, in-vitro residence time, vapor transmissiontest and in-vitro (cellophane, egg membrane) and exvivo(goat buccal mucosa) release. Formulations Ha2(2%) HPMC K100M CR and Pa4 (4%) HPMC K15showed good mucoadhesive strength, in-vitro and exvivoresidence times, with controlled release for 10hours.

Solid State Characterization and Effect of PEG 20000 and Lecithin on Particle Size Reduction and Stability of Complexed Glibenclamide Nanocrystals.

Aims: To formulate and characterize GLB-PEG-LEC NCs (lecithin complexed Glibenclamide nanocrystals) and to analyze the effect of PEG 20000 and lecithin on drug properties, particle size reduction and stability of GLB NCs. Study Design: Precipitated (GLB-PEG) and complexed nanocrystals (GLB-PEG-LEC) of glibenclamide were characterized for particle size, size distribution, zeta potential and stability assessment using photon correlation spectroscopy. The crystallinity was analyzed by X-ray powder diffraction spectroscopy and differential scanning calorimetry. The chemical stability was assessed by means of infrared spectroscopy and surface morphology by scanning electron microscopy. Place and Duration of Study: Asian Institute of Medicine Science and Technology, Malaysia, between May 2102 and June 2013. Methodology: GLB-PEG NCs were prepared by precipitation technique using PEG 20000 and complexed by soybean lecithin. The effect of lecithin in particle size reduction, change in crystallinity, stability and surface properties of NCs were analyzed and compared with pure glibenclamide (GLB) and precipitated NCs. The formulations were optimized and its stability was assessed during a 3 month period. Results: Pure GLB exhibited an average particle size of 1551 nm. The average particle size of precipitated NCs was between 236 - 7000 nm, while that of complexed NCs was between 155 - 842 nm. The particle size of NC was found to decrease, whereas its zeta potential was found to increase after complexation. DSC studies showed no change in crystalline structure. PXRD studies proved that crystallinity was maintained in NCs. SEM analysis showed presence of spherical shape particles with a lipid coat on the surface after complexation. Stability studies revealed no change in particle size during 3 month period. FTIR studies showed the compatability of excipients with the drug. Conclusion: These results show that lecithin complexed GLB NCs could be utilized as promising carriers in development of various formulations due to its high stability and decreased particle size.

An Investigation on Enhancement of Solubility of 5 Fluorouracil by Applying Complexation Technique- Characterization, Dissolution and Molecular-Modeling Studies.

The drug 5 fluorouracil is sparingly soluble in water. The aqueous solubility and dissolution rate of 5-fluorouracil can be increased by inclusion complexation with β-cyclodextrin. Molecular-modeling studies support the formation of stable molecular inclusion complexation of 5-fluorouracil with β-cyclodextrin monomer (1:1). Complexes were prepared by physical mixture, kneading, co evaporation and freeze drying methods. Two ratios 1:1 and 1:2 were formulated. These eight complexes were subjected to Phase-solubility study, molecular modeling and dissolution study. The complexes formed were confirmed by DSC studies. Phase solubility profile indicated that the solubility of 5-fluorouracil increased in the presence of β-cyclodextrin monomer. Results obtained by different characterization techniques clearly indicate that the freeze-drying method leads to formation of solid state complexes between 5-fluorouracil and β-cyclodextrin. The complexation of 5-fluorouracil with β- cyclodextrin lends an ample credence for better therapeutic efficacy.

Aroylhydrazones as potential systems for information storage: photoisomerization and metal complexation / Las aroilhidrazonas como sistemas potenciales para el almacenamiento de información: fotoisomerización y complejación de metales. / Aroylhydrazones como sistemas potenciais para o armazenamento de informação: fotoisomerização e complexação de metais

Aroylhydrazones are compounds formed from the condensation of an acylhydrazine and an aldehyde. These compounds exhibit dynamic reversible properties such as isomerization photochemically and thermally activated, hydrazine substitution and coordination to metallic centers. All these together represent systems with multiple dynamics suitable for information storage devices and for the design of molecular photoswitches.

Las aroilhidrazonas son compuestos formados a partir de la condensación de una acilhidrazina y un aldehído. Estos compuestos presentan propiedades dinámicas reversibles tales como la isomerización activada térmica y fotoquímicamente, la sustitución de hidracina y la coordinación con centros metálicos. Todas estas representan sistemas con dinámicas múltiples apropiadas para dispositivos de almacenamiento de información y para el diseño de foto-interruptores moleculares.

Aroilhidrazonas são compostos formados a partir da condensação de uma acilhidrazina e um aldeído. Estes compostos apresentam propriedades reversíveis dinâmicas, como isomerização fotoquímica e termicamente ativada, substituição de hidrazina e coordenação de centros metálicos. Todos estes em conjunto representam sistemas com múl350 Revista Colombiana de Química, Volumen 41, nro. 3 de 2012 tiplas dinâmicas adequadas para dispositivos de armazenamento de informações e para o desenho de fotodispositivos moleculares.

Complexação de íons de metais por matéria orgânica dissolvida: modelagem e aplicação em sistemas reais

Metal ions are known by their physiological and industrial importance as well as by their environmental risk aspects. To elucidate the behavior of these elements in superficial water bodies, it is necessary to understand the various occurring interactions, mainly those related to the chemical speciation. One of the most important processes that metal species undergo in natural aquatic bodies is their interaction with dissolved organic matter (DOM), which can happen through adsorption, ionic exchange and complexation. In this work, laboratory experiments with Cu(II), Pb(II) and Cd(II) ions and commercial humic acid were made under various conditions (ionic strength and buffering) to test the van den Berg and Kramer complexation model. After the simulation, the model was used to determine the Cu(II), Pb(II) and Cd(II) complexation capacity of natural waters from three important rivers in the state of Maranhao, Brazil (Itapecuru, Bacanga and Pericuma rivers). The dissolved organic carbon (DOC) concentration was used to express the DOM concentration. The results confirmed that there is a strong interaction between the DOM and metal ions, and that the van den Berg and Kramer model (with one coordination site) is suitable for estimating the complexation constant (K) and the ligand site concentration (Lt). The simulated water samples used in the laboratory showed the complexation order: Cu(II) > Cd(II) > Pb(II); and the complexation capacity was directly proportional to the humic acid concentration. We believe that the smaller Cu(II) ionic radius yields a stronger affinity with the DOM. In the experiments with natural waters, the river with more DOC (Bacanga river) showed better complexation capacity; however, the order was Pb(II) > Cu(II) > Cd(II) probably because of the presence of appreciable concentrations of Cu(II) in natural waters.

Os íons de metais pesados são conhecidos tanto pela sua importância fisiológica e industrial, bem como pelo risco ambiental e à saúde humana. Para elucidar o comportamento dessas espécies nos corpos hídricos, os quais recebem grande parte da descarga de metais, seja de origem antrópica ou por fontes naturais, é necessário entender as interações que elas apresentam com o meio, principalmente a especiação química. Um dos mais importantes processos pelos quais passam as espécies metálicas em corpos aquáticos naturais é a interação com a matéria orgânica dissolvida (MOD), que pode ser por adsorção, reações de troca iônica ou por complexação. Neste trabalho foram realizados vários experimentos com o objetivo de descrever o comportamento da complexação de três importantes cátions Cu(II), Cd(II) e Pb(II) com a matéria orgânica (ácido húmico comercial), sob condições diversas de força iônica em meio tamponado. Os resultados foram avaliados de acordo com o modelo de van den Berg e Kramer para a complexação de metais. O modelo foi aplicado na determinação da capacidade de complexação dos íons em amostras reais, oriundas de três rios maranhenses que integram a Amazônia legal: Itapecuru, Bacanga e Pericumã. Nas águas dos rios utilizou-se o parâmetro carbono orgânico dissolvido (COD) para expressar a MOD. Os resultados confirmaram forte interação entre a MOD e íons de metais pesados e que o modelo de van den Berg e Kramer é satisfatório para se estimar a constante de complexação (K) e a concentração de sítios de complexação (Lt). Nas amostras simuladas em laboratório a ordem de complexação dos metais foi Cu(II) > Cd(II) > Pb(II) e a capacidade de complexação mostrou ser linear em função da concentração de ácido húmico comercial. Acredita-se que por ter menor raio iônico, o íon Cu(II) possui maior afinidade com os sítios de complexação. Nas amostras retiradas dos corpos aquáticos, observou-se que o rio com maior concentração de COD (rio Bacanga) apresentou maior capacidade de complexação; entretanto, a ordem foi Pb(II) > Cu(II) > Cd(II) provavelmente devido à presença de íons Cu(II) em maior quantidade nas águas dos rios.

Solos subtropicais de altitude: atributos químicos, teor de matéria orgânica e resistência à oxidação química / Highland subtropical soils: chemical attributes, content of organic matter and its resistance to chemical oxidation

Neste trabalho foram estudadas amostras de horizontes A de oito solos representativos da região Campos de Cima da Serra, Rio Grande do Sul, sendo determinados: textura, pH em água, CTC a pH 7, teores de Al trocável e de óxidos de Fe (Fed e Feo). As amostras foram tratadas com peróxido de hidrogênio e, antes e após tratamento, foram determinados teores de C e de N e realizada análise por espectroscopia de infra-vermelho com transformada de Fourier (FTIR). O teor de C foi alto (4 a 23 por cento) e sua variação correlacionou-se com a altitude e com o teor de Al trocável, sugerindo que a menor temperatura e a complexação com Al iônico contribuem para a estabilização da matéria orgânica do solo (MOS). A proporção de carbono do solo resistente à oxidação variou de 1 a 16 por cento e correlacionou-se com a razão Feo/Fed. A estabilização desta fração da MOS foi atribuída à interação de grupos carboxílicos ligados a estruturas alifáticas e aromáticas com óxidos de Fe de baixa cristalinidade.

In this research, texture, soil pH, CEC at pH 7, exchangeable Al, and content of Fe-oxides (Fed and Feo) were determined in A horizons samples of eight representative soils under native pasture from Campos de Cima da Serra, Rio Grande do Sul State, Brazil. The samples were treated with hydrogen peroxide and, before and after the treatment, C and N contents were determined and Fourier Transformed Infra-red (FTIR) spectroscopy was performed. The content of soil C was high (4 to 23 percent) and its variation correlated with the altitude and exchangeable Al indicating that lower temperatures and complexation with ionic Al contribute to soil organic matter (SOM) stabilization. The proportion of oxidation-resistant carbon varied between 1 and 16 percent and correlated with the ratio Feo/Fed. The stabilization of this SOM fraction was assigned to the interaction of carboxylic groups bound to aromatic and aliphatic structures with Fe-oxides of low crystallinity degree.