Manuel I. Velasco

Differential scanning potentiometry: surface charge development and apparent dissociation constants of natural humic acids.

Humic acids (HA) are the main components of soil organic matter which can form complexes with metal ions and other soil and/or water contaminants. Here, we focus on their acid-base properties. HA were extracted from two different soils (Tipic Ustifluvent and Entic Haplustoll) with different vegetation. In this study we use a simple method, differential scanning potentiometry (DSP), to determine HA buffer capacity distribution, apparent dissociation constant values and surface charge development.

Evaporation Kinetics in Swollen Porous Polymeric Networks

NMR is a fast, nondestructive, and noninvasive technique that can provide information about the pore structure of macroporous polymer beads and the dynamics of liquids confined in them. In this work, we describe the study of the pore structure of the macroporous polymer of ethylene glycol dimethacrylate and 2-hydroxyethyl methacrylate [poly(EGDMA-co-HEMA)] in the dry but also in the swollen state by measuring relaxation times of liquids contained in the polymer network. The results show that the pore architecture differs from the dry to the soaked state. The behavior of polar liquids during evaporation and deswelling dynamics is monitored and described. An internal migration of water from the swollen polymer mesh into expanding pores takes place. With this procedure it is possible to obtain information about the microscopic morphology behavior of the matrix during evaporation and deswelling. This information is of great interest with the aspect of possible and future applications for these types of materials.

Enhanced Surface Interaction of Water Confined in Hierarchical Porous Polymers Induced by Hydrogen Bonding

Hierarchical porous polymer systems are increasingly applied to catalysis, bioengineering, or separation technology because of the versatility provided by the connection of mesopores with percolating macroporous structures. Nuclear magnetic resonance (NMR) is a suitable technique for the study of such systems as it can detect signals stemming from the confined liquid and translate this information into pore size, molecular mobility, and liquid-surface interactions. We focus on the properties of water confined in macroporous polymers of ethylene glycol dimethacrylate and 2-hydroxyethyl methacrylate [poly(EGDMA-co-HEMA)] with different amounts of cross-linkers, in which a substantial variation of hydroxyl groups is achieved. As soft polymer scaffolds may swell upon saturation with determined liquids, the use of NMR is particularly important as it measures the system in its operational state. This study combines different NMR techniques to obtain information on surface interactions of water with hydrophilic polymer chains. A transition from a surface-induced relaxation in which relaxivity depends on the pore size to a regime where the organic pore surface strongly restricts water diffusion is observed. Surface affinities are defined through the molecular residence times near the network surface.

CHARACTERIZATION OF HUMIC ACIDS ORIGINATED FROM ARGENTINEAN COMPOST AND SOIL BY CAPILLARY ELECTROPHORESIS AND MASS SPECTROMETRY

Humic acids (HAs) extracted from different organic compost and soil from Argentina have been characterized by capillary electrophoresis (CE) and mass spectrometry. The chemical properties of HAs show changes depending on their origin (compost, soil). Capillary electrophoresis analyses were carried out using a background electrolyte consisting of boric acid, TRIS and EDTA (BTE). BTE was also modified with cyclodextrins. After optimization of BTE, the best results were obtained when b-cyclodextrin was used. Under optimized separation conditions, the characteristics CE fingerprints of compost derived HAs (CHAs) were studied. CE fingerprints show differences in the composition of the different CHAs. Mass spectra obtained by laser desorption ionization time of flight mass spectrometry show differences between the CHAs and HAs extracted from Argentinean soil. A comparison with the soil standard HAs (International Humic Substances Society) was made. CHAs show mostly compounds in the mass spectra with low m/z values. The typical patterns exhibited in soil HAs of different origin are present in the Argentinean soil HA, i.e. groups of peaks around mass-to-charge (m/z) 800

Spatially Resolved Monitoring of Drying of Hierarchical Porous Organic Networks

Evaporation kinetics of water confined in hierarchal polymeric porous media is studied by low field nuclear magnetic resonance (NMR). Systems synthesized with various degrees of cross-linker density render networks with similar pore sizes but different response when soaked with water. Polymeric networks with low percentage of cross-linker can undergo swelling, which affects the porosity as well as the drying kinetics. The drying process is monitored macroscopically by single-sided NMR, with spatial resolution of 100 μm, while microscopic information is obtained by measurements of spin-spin relaxation times (T2). Transition from a funicular to a pendular regime, where hydraulic connectivity is lost and the capillary flow cannot compensate for the surface evaporation, can be observed from inspection of the water content in different sample layers. Relaxation measurements indicate that even when the larger pore structures are depleted of water, capillary flow occurs through smaller voids.

Characterization of humic acids derived from rabbit manure treated by composting-vermicomposting process

The aim of this work was to evaluate, through different analytical techniques, the evolution of some chemical and physicochemical properties of humic acid (HA)-like fraction extracted from an organic amendment, like rabbit manure, handle with composting followed by vermicomposting process, in comparison with soil HA, in order to reach an appropriate criterion to evaluate the maturity of an organic amendment. The raw material used was rabbit manure treated with composting followed by vermicomposting process. Soil and organic amendments were analyzed by chemical properties. The HA was extracted from the amendments samples and from an Entic Haplustol and analyzed the chemical and physicochemical characteristics by several analytical methods. Through these analytical techniques was possible to follow the evolution of the HA-like fraction during this stabilization-maturation process Through the composting followed by vermicomposting process the HA-like fraction are evolving toward more stable and complex macromolecule resembling native soil HA.

Synthesis of amphiphilic dendrons and their interactions in aqueous solutions with cetyltrimethylammonium p-toluenesulfonate (CTAT)

In this work, we report synthesis and rheology of an interesting structured fluid based on the self-assembly of amphiphilic dendrons and wormlike micelles. Two amphiphilic dendrons were synthesized by the combination of aliphatic chains and polar dendritic heads. They showed different degrees of hydrophobicity and formed micelles in aqueous solution at critical micelle concentrations (CMC) of 25 and 125 ppm. The dendrons were soluble in water up to a concentration of approximately 1200 ppm, and produced no measurable increase in the viscosity of the solvent. The rheology of solutions of mixtures of each dendron with cetyltrimethylammonium p-toluenesulfonate (CTAT, a cationic surfactant) was characterized in simple shear flow. In the concentration range in which CTAT forms semidilute solutions of wormlike micelles, dendron addition produced a substantial synergy in zero-shear rate viscosity. Parallel-plate oscillatory shear measurements demonstrated that the CTAT/dendron mixtures are significantly more elastic than CTAT solutions. The viscosity synergy occurs at dendron concentrations lower than their CMC, and it is stronger for the more hydrophobic dendron. This suggests that the interactions between dendrons and wormlike micelles are basically hydrophobic, which implies attachment of dendron micelles to wormlike CTAT micelles in a manner similar to micellization of surfactants on polyelectrolytes.

Fruits of the glossy privet (Ligustrum lucidum—Oleaceae) as biocatalysts for producing chiral aromatic alcohols

Abstract The screening of four invasive plant species for use as biocatalysts in the stereoselective reduction of ketones is reported. Our studies revealed that fruits of Ligustrum lucidum can be used for the bioreduction of acetophenone to (S)-1-phenylethanol (94% conversion, > 99 enantiomeric excess [ee]%). Using this methodology, 13 substituted (S)-phenylethanols were synthesized with good ee values (> 99.9 to 78%) using a technique which is more environmentally friendly than classical reduction of prochiral ketones. The results reveal the fruits of L. lucidum to be promising biocatalysts for the production of key intermediates.

Alternatives to free molecular halogens as chemoselective reactants: Catalysis of organic reactions with reusable complexes of halogen metal salts

Organometallic complexes of halogen metallic salts have been used as catalysts in different organic reactions, mainly the oxidation of organic compounds. Their use has not only allowed the reduction of the amounts of catalyst (since they can be reused) but also a lower generation of byproducts and wastes. The different reaction media developed through the research were analyzed by several green parameters, and the best results were obtained with complexes that have cyclodextrins as organic ligands. The proposed methodology is an alternative to use of molecular halogen as oxidant or catalyst when halogens are significant chemoselective reactants.

Fire Impact on Several Chemical and Physicochemical Parameters in a Forest Soil

Cordoba is a Mediterranean State, with semiarid climate, dry autumn and winter, in which the wild fire can take place, especially at the end of dry season. Forest fires happen frequently in the mountain zones of the province of Cordoba, Argentina, which are located at west and south-west region. The vegetation, in the south-west zone, are principally Pinus halepensis Mill.; Pinus elliottii implanted and the native vegetation cover is Stipa caudata, Piptochaetium hackelii, P. napostaense y Briza subaristata, between others. Taxonomically the soil corresponds to an Ustorthent. In the west area the native vegetation is principally Acacia caven, Festuca hieronymi, Stipa, Poa stukerti, between others. The soil is an Argiustoll. Forest wild fires constitute a serious environmental problem, not only due to the destruction of vegetation but also because the degradation that may be induced in a soil as a consequence of the change produced in its properties. Wild fire can strongly modify the abiotic and biotic characteristics of soil, altering its structure, chemical and physicochemical properties, carbon content and macronutrient levels. The degree of the alteration produced depends on the frequency and intensity of fire, all these modifications being particularly important in the surface horizons. Organic matter is a key factor for forest soil. It has a direct and /or an indirect influence on all physical and chemical characteristics of the soil. While low severity fires, such as those prescribed for forest management, have been reported to have transient but positive effect on soil fertility, severe wildfire result in significant losses of soil organic matter, and nutrient, and deterioration of the overall physical-chemical properties of soil that determine its fertility, such as porosity, structure among others (Certini, 2005). Fire may directly consume part or all of the standing plant material and litter as well as the organic matter in the upper layer of the soil. One of the most important soil change, during the burning is the alteration in the organic matter content therefore, the nutrient contained in the organic matter are either more available or can be volatilized and lost from the site. The soluble nutrient would be loss for erosion or leaching if they are not immediately absorbed by plants or retained by soil. Humic substances are one of the most important fractions of the organic matter and are considered the most abundant organic component in nature and largely contribute to soil structuring and stability, to its permeability for water and gases, to its water holding