Modelling Polyphenol Extraction through Ultrasound-Assisted Extraction by Machine Learning in Olea europaea Leaves

The study of the phenolic compounds present in olive leaves (Olea europaea) is of great interest due to their health benefits. In this research, different machine learning algorithms such as RF, SVM, and ANN, with temperature, time, and volume as input variables, were developed to model the extract yield and the total phenolic content (TPC) from experimental data reported in the literature. In terms of extract yield, the neural network-based ANNZ-L model presents the lowest root mean square error (RMSE) value in the validation phase (9.44 mg/g DL), which corresponds with a mean absolute percentage error (MAPE) of 3.7%. On the other hand, the best model to determine the TPC value was the neural network-based model ANNR, with an RMSE of 0.89 mg GAE/g DL in the validation phase (MAPE of 2.9%). Both models obtain, for the test phase, MAPE values of 4.9 and 3.5%, respectively. This affirms that ANN models would be good modelling tools to determine the extract yield and TPC value of the ultrasound-assisted extraction (UAE) process of olive leaves under different temperatures, times, and solvents.

Oxidation of Aldehydes Used as Food Additives by Peroxynitrite

Benzaldehyde and its derivatives are used as food supplements. These substances can be used mainly as flavorings or as antioxidants. Besides, peroxynitrite, an oxidizing agent, could be formed in canned food. Both species could react between them. The present article has focused on the kinetic study of the oxidation of aldehydes by peroxynitrite. A reaction mechanism that justifies all the experimental results is proposed. This mechanism, in acidic media, passes through three competitive pathways: (a) a radical attack that produces benzoic acid. (b) peracid oxidation, and (c) a nucleophilic attack of peroxynitrous acid over aldehyde to form an intermediate, X, that produces benzoic acid, or, through a Cannizzaro-type reaction, benzoic acid and benzyl alcohol. All rate constants involved in the third pathway (c) have been calculated. These results have never been described in the literature in acid media. A pH effect was analyzed.

The Chemical, Microbiological and Volatile Composition of Kefir-Like Beverages Produced from Red Table Grape Juice in Repeated 24-h Fed-Batch Subcultures

The aim of this work was to study the production of kefir-like beverages via the fed-batch fermentation of red table grape juice at initial pHs of 3.99 (fermentation A) and 5.99 (fermentation B) with kefir grains during 4 repeated 24-h fed-batch subcultures. All kefir-like beverages (KLB) were characterized by low alcoholic grade (≤3.6%, v/v) and lactic and acetic acid concentrations. The beverages obtained from fermentation B had lower concentrations of sugars and higher microbial counts than the KLB obtained in fermentation A. Additionally, the KLB samples from fermentation B were the most aromatic and had the highest contents of alcohols, esters, aldehydes and organic acids, in contrast with the nonfermented juice and KLB from fermentation A. These results indicate the possibility of obtaining red table grape KLB with their own distinctive aromatic characteristics and high content in probiotic viable cells, contributing to the valorization of this fruit.

Benefits, toxicity and current market of cannabidiol in edibles

The commercialization of products with cannabidiol (CBD) has undergone a significant increase. These products can be presented in different forms such as baked goods, gummies or beverages (such as kombucha, beer or teas, among others) using wide concentrations ranges. The use of CBD in edibles favors its consumption, for medicinal users, during the work week, avoid its possible social stigma and facilitates its transport. These products can be purchased on store shelves and online. There is a large number of specialized studies, in which the possible advantages of CBD consumption are described in the preclinical and clinical trials. It is also necessary to recognize the existence of other works revealing that the excessive consumption of CBD could have some repercussions on health. In this review, it is analyzed the composition and properties of Cannabis sativa L., the health benefits of cannabinoids (focusing on CBD), its consumption, its possible toxicological effects, a brief exposition of the extraction process, and a collection of different products that contain CBD in its composition.

Essential Oils as Antimicrobials in Crop Protection

At present, organic crops have reached an important boom in a society increasingly interested in the conservation of the environment and sustainability. It is evident that a part of the population in the Western world focuses their concern on how to obtain our food and on doing it in a way that is as respectful as possible with the environment. In this review, we present a compilation of the work carried out with the use of essential oils as an alternative in the fight against different bacteria and fungi that attack crops and related products. Given the collected works, the efficacy of essential oils for their use as pesticides for agricultural use is evident.

Mitigation of emerging implications of climate change on food production systems

Crops, livestock and seafood are major contributors to global economy. Agriculture and fisheries are especially dependent on climate. Thus, elevated temperatures and carbon dioxide levels can have large impacts on appropriate nutrient levels, soil moisture, water availability and various other critical performance conditions. Changes in drought and flood frequency and severity can pose severe challenges to farmers and threaten food safety. In addition, increasingly warmer water temperatures are likely to shift the habitat ranges of many fish and shellfish species, ultimately disrupting ecosystems. In general, climate change will probably have negative implications for farming, animal husbandry and fishing. The effects of climate change must be taken into account as a key aspect along with other evolving factors with a potential impact on agricultural production, such as changes in agricultural practices and technology; all of them with a serious impact on food availability and price. This review is intended to provide critical and timely information on climate change and its implications in the food production/consumption system, paying special attention to the available mitigation strategies.

The Potential of Seaweeds as a Source of Functional Ingredients of Prebiotic and Antioxidant Value

Two thirds of the world is covered by oceans, whose upper layer is inhabited by algae. This means that there is a large extension to obtain these photoautotrophic organisms. Algae have undergone a boom in recent years, with consequent discoveries and advances in this field. Algae are not only of high ecological value but also of great economic importance. Possible applications of algae are very diverse and include anti-biofilm activity, production of biofuels, bioremediation, as fertilizer, as fish feed, as food or food ingredients, in pharmacology (since they show antioxidant or contraceptive activities), in cosmeceutical formulation, and in such other applications as filters or for obtaining minerals. In this context, algae as food can be of help to maintain or even improve human health, and there is a growing interest in new products called functional foods, which can promote such a healthy state. Therefore, in this search, one of the main areas of research is the extraction and characterization of new natural ingredients with biological activity (e.g., prebiotic and antioxidant) that can contribute to consumers' well-being. The present review shows the results of a bibliographic survey on the chemical composition of macroalgae, together with a critical discussion about their potential as natural sources of new functional ingredients.

Interaction of Caffeic Acid with SDS Micellar Aggregates

Micellar systems consisting of a surfactant and an additive such as an organic salt or an acid usually self-organize as a series of worm-like micelles that ultimately form a micellar network. The nature of the additive influences micellar structure and properties such as aggregate lifetime. For ionic surfactants such as sodium dodecyl sulfate (SDS), CMC decreases with increasing temperature to a minimum in the low-temperature region beyond which it exhibits the opposite trend. The presence of additives in a surfactant micellar system also modifies monomer interactions in aggregates, thereby altering CMC and conductance. Because the standard deviation of β was always lower than 10%, its slight decrease with increasing temperature was not significant. However, the absolute value of Gibbs free enthalpy, a thermodynamic potential that can be used to calculate the maximum of reversible work, increased with increasing temperature and caffeic acid concentration. Micellization in the presence of caffeic acid was an endothermic process, which was entropically controlled. The enthalpy and enthropy positive values resulted from melting of "icebergs" or "flickering clusters" around the surfactant, leading to increased packing of hydrocarbon chains within the micellar core in a non-random manner. This can be possibly explained by caffeic acid governing the 3D matrix structure of water around the micellar aggregates. The fact that both enthalpy and entropy were positive testifies to the importance of hydrophobic interactions as a major driving force for micellization. Micellar systems allow the service life of some products to be extended without the need to increase the amounts of post-harvest storage preservatives used. If a surfactant is not an allowed ingredient or food additive, carefully washing it off before the product is consumed can avoid any associated risks. In this work, we examined the influence of temperature and SDS concentration on the properties of SDS⁻caffeic acid micellar systems. Micellar properties can be modified with various additives to develop new uses for micelles. This allows smaller amounts of additives to be used without detracting from their benefits.

A critical review on the use of artificial neural networks in olive oil production, characterization and authentication

Artificial neural networks (ANN) are computationally based mathematical tools inspired by the fundamental cell of the nervous system, the neuron. ANN constitute a simplified artificial replica of the human brain consisting of parallel processing neural elements similar to neurons in living beings. ANN is able to store large amounts of experimental information to be used for generalization with the aid of an appropriate prediction model. ANN has proved useful for a variety of biological, medical, economic and meteorological purposes, and in agro-food science and technology. The olive oil industry has a substantial weight in Mediterranean's economy. The different steps of the olive oil production process, which include olive tree and fruit care, fruit harvest, mechanical and chemical processing, and oil packaging have been examined in depth with a view to their optimization, and so have the authenticity, sensory properties and other quality-related properties of olive oil. This paper reviews existing literature on the use of bioinformatics predictive methods based on ANN in connection with the production, processing and characterization of olive oil. It examines the state of the art in bioinformatics tools for optimizing or predicting its quality with a view to identifying potential deficiencies or aspects for improvement.

A critical review on the applications of artificial neural networks in winemaking technology

Since their development in 1943, artificial neural networks were extended into applications in many fields. Last twenty years have brought their introduction into winery, where they were applied following four basic purposes: authenticity assurance systems, electronic sensory devices, production optimization methods, and artificial vision in image treatment tools, with successful and promising results. This work reviews the most significant approaches for neural networks in winemaking technologies with the aim of producing a clear and useful review document.

Redispersion and Self-Assembly of C60 Fullerene in Water and Toluene

This work aims at assessing the influence of two different solvents, bidistilled water and toluene, on dispersions of carbon-based engineered nanomaterials, namely, fullerenes, and their self-assembly behavior. The obtained self-assembled carbon-based materials were characterized using UV-vis spectrophotometry and transmission electron microscopy techniques. The results obtained were unexpected when toluene was used for dispersing fullerene C₆₀, with the formation of two different types of self-assembled structures: fullerene C₆₀ nanowhiskers (FNWs) and a type of quasispherical nanostructure. The FNWs ranged between 1 and 6 μm in length, whereas the quasispherical fullerene C₆₀ nanoaggregates ranged between 10 and 50 nm in diameter. Aggregates obtained in toluene showed a well-formed crystal structure. When using water, the obtained aggregates were amorphous and showed a no well-defined shape. Their sizes ranged between 20 and 40 nm for nanosized structures and between 0.4 and 4.8 μm for micron-sized self-aggregates.

Airborne castanea pollen forecasting model for ecological and allergological implementation

Castanea sativa Miller belongs to the natural vegetation of many European deciduous forests prompting impacts in the forestry, ecology, allergological and chestnut food industry fields. The study of the Castanea flowering represents an important tool for evaluating the ecological conservation of North-Western Spain woodland and the possible changes in the chestnut distribution due to recent climatic change. The Castanea pollen production and dispersal capacity may cause hypersensitivity reactions in the sensitive human population due to the relationship between patients with chestnut pollen allergy and a potential cross reactivity risk with other pollens or plant foods. In addition to Castanea pollen's importance as a pollinosis agent, its study is also essential in North-Western Spain due to the economic impact of the industry around the chestnut tree cultivation and its beekeeping interest. The aim of this research is to develop an Artificial Neural Networks for predict the Castanea pollen concentration in the atmosphere of the North-West Spain area by means a 20years data set. It was detected an increasing trend of the total annual Castanea pollen concentrations in the atmosphere during the study period. The Artificial Neural Networks (ANNs) implemented in this study show a great ability to predict Castanea pollen concentration one, two and three days ahead. The model to predict the Castanea pollen concentration one day ahead shows a high linear correlation coefficient of 0.784 (individual ANN) and 0.738 (multiple ANN). The results obtained improved those obtained by the classical methodology used to predict the airborne pollen concentrations such as time series analysis or other models based on the correlation of pollen levels with meteorological variables.

Application of transit data analysis and artificial neural network in the prediction of discharge of Lor River, NW Spain

Transit data analysis and artificial neural networks (ANNs) have proven to be a useful tool for characterizing and modelling non-linear hydrological processes. In this paper, these methods have been used to characterize and to predict the discharge of Lor River (North Western Spain), 1, 2 and 3 days ahead. Transit data analyses show a coefficient of correlation of 0.53 for a lag between precipitation and discharge of 1 day. On the other hand, temperature and discharge has a negative coefficient of correlation (-0.43) for a delay of 19 days. The ANNs developed provide a good result for the validation period, with R(2) between 0.92 and 0.80. Furthermore, these prediction models have been tested with discharge data from a period 16 years later. Results of this testing period also show a good correlation, with R(2) between 0.91 and 0.64. Overall, results indicate that ANNs are a good tool to predict river discharge with a small number of input variables.

Percolative Behavior Models Based on Artificial Neural Networks for Electrical Percolation of AOT Microemulsions in the Presence of Crown Ethers as Additives

A series of models, based on artificial neural networks, of the percolative behaviour of AOT microemulsions in the presence of crown ethers as additives have been developed. Input variables, related to the chemical structure of crown ethers and their packing with surfactant film, have been selected. As a result, a model has been chosen with a good forecast capability for percolation threshold of such microemulsions.

Percolation Threshold of AOT Microemulsions with n-Alkyl Acids as Additives Prediction by Means of Artificial Neural Networks

Different artificial neural networks architectures have been assayed to predict percolation temperature of AOT/iC8/H2O microemulsions in the presence of n-alkyl acids with a chain length between 0 and 24 carbons, using a multilayer perceptron with five easy-acquired entrance variables (number of carbons, log P, length of the hydrocarbon chain, pKa and acid concentration). The evaluation of the neural networks was carried out by means of RMSE and IDP, resulting that the architecture with better results consists in five input neurons, two middle layers (with five and ten neuron respectively) and one output neuron. Results prove that Artificial Neural Networks are a useful tool elaborating models to predict percolation temperature of microemulsion systems in the presence of additives.

Stability study of Iprodione in alkaline media in the presence of humic acids

The influence of humic aggregates in water solution upon the chemical stability of Iprodione has been investigated under basic conditions. Taking into account that an important part of soils are colloids, the possibility of its presence implies that soil composition and its structure will play an important role in the stability of this pesticide. A kinetic model was applied to this system and the kinetic coefficients were obtained. An inhibition upon the alkaline hydrolysis of Iprodione (2-fold) was observed and it was rationalized in terms of the micellar pseudophase model. These results have been compared with the corresponding ones in the same natural colloidal aggregates in the presence of other pesticides.

Predicting Critical Micelle Concentration Values of Non-Ionic Surfactants by Using Artificial Neural Networks

Critical Micelle Concentration is a fundamental property on studying behaviour of surfactants. In general terms it depends on temperature, pressure and on the existence and concentration of other surface-active substances and electrolytes. In this work it is presented a model based on Artificial Neural Networks to obtain predictive values of Critical Micelle Concentration (CMC) of some non-ionic surfactants. ANN model works using topological descriptors of the molecules involved together with already known CMC values and provides predictive values for new cases. It is proposed a specific architecture for ANN consisting of an input layer with seven neurons, one intermediate layer with fourteen neurons and one neuron in the output layer. This ANN model seems to be a good method for forecast CMC.

Degradation of carbofuran and carbofuran-derivatives in presence of humic substances under basic conditions

The influence of humic aggregates in water solution upon the chemical stability of carbofuran (CF) and the carbofuran-derivatives, 3-hydroxy-carbofuran (HCF) and 3-keto-carbofuran (KCF), has been investigated in basic media. An inhibition upon the basic hydrolysis of 3-hydroxy-carbofuran and 3-keto-carbofuran (≈ 1.7 and ≈ 1.5-fold, respectively) was observed and it was rationalized in terms of the micellar pseudophase model. Nevertheless, non-significant effect upon the carbofuran stability was found in the presence of humic substances. These behaviors have been compared with the corresponding ones in other synthetic colloidal aggregates.

Evaluation of atmospheric Poaceae pollen concentration using a neural network applied to a coastal Atlantic climate region

In the South of Europe an important percentage of population suffers pollen allergies, being the Poaceae pollen the major source. One of aerobiology's objectives is to develop statistical models enabling the short- and long-term prediction of atmospheric pollen concentrations to take preventative measures to protect allergic patients from the severity of the atmospheric pollen season. The implementation of a computational model based on supervised MLP neural network was applied for the prediction of the atmospheric Poaceae pollen concentration. There is a good correlation between the values predicted by the ANN for the training cases in comparison with the real pollen concentrations. A high coefficient of linear regression (R(2)) of 0.9696 was obtained. The accuracy of the neural network developed was tested with data from 2006 and 2007, which was not taken into account to establish the aforementioned models. Neural networks provided us a good tool to forecasting allergenic airborne pollen concentration helping the automation of the prediction system in the aerobiological information diffusion to the population suffering from allergic problems.

First kinetic discrimination between carbon and oxygen reactivity of enols

Nitrosation of enols shows a well-differentiated behavior depending on whether the reaction proceeds through the carbon (nucleophilic catalysis is observed) or the oxygen atom (general acid-base catalysis is observed). This is due to the different operating mechanisms for C- and O-nitrosation. Nitrosation of acetylacetone (AcAc) shows a simultaneous nucleophilic and acid-base catalysis. This simultaneous catalysis constitutes the first kinetic evidence of two independent reactions on the carbon and oxygen atom of an enol. The following kinetic study allows us to determine the rate constants for both reaction pathways. A similar reactivity of the nucleophilic centers with the nitrosonium ion is observed.

Simultaneous effect of microemulsions and phase-transfer agents on aminolysis reactions

The catalytic effect of triethylene glycol dimethyl ether (glyme) on the butylaminolysis of 4-nitrophenylcaprate (NPC) in water/AOT/chlorobenzene microemulsions has been studied. Experimental results show the existence of four simultaneous reaction pathways. One of them takes place at the microemulsion interphase where the rate-determining step of butylaminolysis is the formation of the addition intermediate, T+/-. The locus of the other three pathways is the continuous medium of the microemulsion. These three pathways consist of the decomposition of the addition intermediate catalyzed by butylamine, by glyme, and by both of them. The kinetic model allows us to obtain the value of every rate and distribution constant involved in the overall reaction mechanism. We must emphasize that the reactions located in the continuous medium exhibit a kinetic behavior similar to the corresponding one found in pure chlorobenzene. On the basis of the pseudophase model, the percentage of reaction in each of the microdomains of the microemulsion has been calculated. Likewise, changes in the loci of reaction from the interphase to the continuous medium as a function of catalyst concentration have been proved.

Determination of pyridine-2-azo-p-dimethylaniline acidity constants by spectra resolution methodology

The influence of acidity upon the pyridine-2-azo-p-dimethylaniline (PADA) absorption spectrum has been studied. The obtained results allowed us to calculate the acidity constants of PADA. The spectra resolution method has been used to determinate the constants. The absorption spectrum was decomposed in two sub-bands for the neutral form of the indicator, one for the monoprotonated molecule and another more for the diprotonated structure. The quantitative analysis of relative areas variation with the medium acidity allows us to obtain the equilibrium constants of PADA prolongation. The obtained values are in good agreement with the values reported in the literature.

Ester aminolysis by morpholine in AOT-based water-in-oil microemulsions

A kinetic study of the aminolysis of p-nitrophenyl acetate (NPA) by morpholine (MOR) in AOT/isooctane/water (w/o) microemulsions was conducted. Based on the solubilities of NPA and MOR in water and isooctane, both compounds partition between the continuous medium, interface and water microdroplets of the microemulsion. Because the rate of the aminolysis reaction decreases with decreasing polarity of the solvent, the reaction must take place to a negligible extent in the continuous medium relative to the interface and the aqueous microdroplets. We used the pseudo-phase model to determine the rate constants at the interface, k(2)(i), and in the water microdroplets, k(2)(w). Both k(2)(i) and k(2)(w) were found to be independent of W in the aminolysis of NPA by MOR. This is a result of the expected increase in k(2)(w) on decreasing W being offset by the decrease in k(2)(i) with increase in the water content of the system. Based on the results, the reaction takes place to an extent of only 16% in the water microdroplets at W=40, the proportion decreasing with decreasing water content.

Influence of aza crown ethers on the electric percolation of AOT/isooctane/water (w/o) microemulsions

A study was carried out on the influence of different aza crown ethers on the electric percolation of AOT/isooctane/water microemulsions. A dual behavior of the aza crown ethers with regard to the percolative phenomenon was observed: low additive concentration causes an increase in the percolation temperature, whereas at high additive concentration a reduction in the percolation temperature of the system was observed. This dual behavior allowed us to define the compensation concentration, which corresponds the aza crown ether concentration at which there is no effect on the percolative phenomenon. We observed a correlation between the effect exerted by the aza crown ethers and the size of the cavity. This shows the importance of the capacity to complexate Na(+) and solubilize it in the interface and the continuous medium on the electric percolation. We also observed a correlation between the effect of the aza crown ethers on the percolation temperature and their external size. This shows the importance of their inclusion in the interface on the percolative phenomenon. Such an inclusion modifies the properties of the AOT film, facilitating the exchange of matter between droplets. A satisfactory multiparametric correlation between the compensation concentration, the distribution of the aza crown ether between water and 1-octanol, and the number of electron-donor atoms (O and N) in the crown ether was obtained. The effects have been compared with those corresponding to the crown ethers.

In Search of Fully Uncomplexed Cyclodextrin in the Presence of Micellar Aggregates

The chemical behavior of beta-cyclodextrin/nonionic surfactant mixed systems has been investigated using the basic hydrolysis of N-methyl-N-nitroso-p-toluenesulfonamide as a chemical probe. The experimental results prove that at the cmc, there are significant quantities of uncomplexed beta-CD in equilibrium with the micellar aggregates. In contrast to the expected situation, the percentage of uncomplexed beta-CD in equilibrium with the micellar system increases on increasing the hydrophobicity of the surfactant molecule. This behavior is due to the existence of two simultaneous processes: complexation of surfactant monomers by cyclodextrin and the process of self-assembly to form micellar aggregates. The autoaggregation of surfactant monomers is expected to be more important than the complexation process in this mixed system. Varying the hydrophobicity of the surfactant monomer enabled us to determine that the percentages of uncomplexed cyclodextrin in equilibrium with the micellar system were in the range of 5-95%.

A New Reaction Pathway in the Ester Aminolysis Catalyzed by Glymes and Crown Ethers

Butylaminolysis of p-nitrophenyl acetate in chlorobenzene in the presence of different kinds of phase-transfer catalysts (crown ethers and glymes) supports the existence of a reaction pathway exhibiting a first-order dependence on the concentration of the phase transfer catalyst and a second-order dependence on the concentration of butylamine. This novel reaction pathway must be included in the mechanism traditionally accepted for the catalysis by phase-transfer agents of aminolysis reactions in aprotic solvents.

Evidence for complexes of different stoichiometries between organic solvents and cyclodextrins

The influence of the organic solvent on the acid and basic hydrolysis of N-methyl-N-nitroso-p-toluenesulfonamide (MNTS) in the presence of alpha- and beta-cyclodextrins has been studied. The observed rate constant was found to decrease through the formation of an unreactive complex between MNTS and the cyclodextrins. In the presence of dioxane, acetonitrile or DMSO, the inhibitory effect of beta-CD decreased on increasing the proportion of organic cosolvent as a result of a competitive reaction involving the formation of an inclusion complex between beta-CD and the cosolvent. The disparate size of the organic solvent molecules resulted in stoichiometric differences between the complexes; the beta-CD-dioxane and beta-CD-DMSO complexes were 1 : 1 whereas the beta-CD-acetonitrile complex was 1 : 2. The basic and acid hydrolysis of MNTS in the presence of alpha-CD showed a different behavior; thus, the reaction gave both 1 : 1 and 2 : 1 alpha-CD-MNTS complexes, of which only the former was reactive. This result was due to the smaller cavity size of alpha-CD and the consequent decreased penetration of MNTS into the cavity in comparison to beta-CD. The acid hydrolysis of MNTS in the presence of alpha-CD also revealed decreased penetration of MNTS into the cyclodextrin cavity, as evidenced by the bound substrate undergoing acid hydrolysis. In addition, the acid hydrolysis of MNTS in the presence of acetonitrile containing alpha-CD gave 1 : 1 alpha-CD-acetonitrile inclusion complexes, which is consistent with a both a reduced cavity size and previously reported data.

First Evidence of Simultaneous Different Kinetic Behaviors at the Interface and the Continuous Medium of w/o Microemulsions

A study was carried out on the butylaminolysis reaction of 4-nitrophenyl caprate in AOT/chlorobenzene/water microemulsions, with the observed rate constant, kobs, showing both first- and second-order dependence on butylamine concentration. The first-order term in [BuNH2] is due to the reaction occurring at the interface of the microemulsion while the second-order term is due to the reaction in the continuous medium. The different kinetic behavior is accounted for by the mechanism by which the reaction proceeds: at the interface of the microemulsion, the rate-determining step is the formation of the addition intermediate, T+/-, whereas in the continuous medium the slow step is the base-catalyzed decomposition of this intermediate. The application of the pseudophase formalism allows the observed kinetic behavior to be explained and to obtain the rate constants at the interface, ki2=0.13 M-1 s-1, and in the continuous medium, ko2KT=2.46x10(-2) M-2 s-1. These values indicate that the reaction rate decreases approximately 23 times upon going from the aqueous medium to the interface of the microemulsion, whereas the rate constant in the continuous medium is consistent with that obtained in pure chlorobenzene, ko2KT=2.09x10(-2) M-2 s-1.

Influence of glymes upon percolative phenomena in AOT-based microemulsions

A study was carried out on the influence of different polyethylene glycol dimethyl ethers (glymes) on the conductance percolation of AOT/isooctane/water microemulsions. The glymes used were chosen on the basis of this chain length (the number of polymeric units). In all cases we observed a decrease in the percolation threshold on increasing the amount of a glyme added to the microemulsion. We observed a correlation between the effect exerted by the glyme and its chain length, which shows the importance of including them in the interface for the percolative phenomenon. Such inclusion modifies the properties of the AOT film, facilitating the exchange of matter between droplets.

Influence of micelles on the basic degradation of carbofuran

The effect of micellar aggregates upon the stability of carbofuran in basic media has been studied. The effect of the presence of micelles upon the basic hydrolysis of carbofuran is a function of the nature of the surfactant monomer. Important catalysis of basic hydrolysis of carbofuran in the presence of colloid aggregates with positive surface charge has been reported. On the other hand, the presence of anionic and nonionic surfactants implies a large inhibition of the basic hydrolysis of carbofuran. Both catalysis and inhibition are due to the association of carbofuran with the micellar core. The kinetic constants for the basic hydrolysis of carbofuran in these microheterogeneous media have been obtained on the basis of a micellar pseudophase model. No significant changes in the intrinsic reactivity of HO- against carbofuran have been observed.

Mixed micelles of alkylamines and cetyltrimethylammonium chloride

The influence of chain length and the nature of the head group on the composition of micelles of a binary mixture of cetyltrimethylammonium chloride with both unsubstituted and N-substituted n-octyl, n-decyl, and n-lauryl amines was established from the variation of the critical micelle concentration (cmc) as a function of the solution composition. A synergistic effect was observed in all instances that were found to be correlated with chain length and the type of N-substituent on the alkylamine head group. Experimental data were compared with theoretical predictions based on the equilibrium between micelles and monomers in solution. The Motomura treatment was used to determine the composition of each compound in the mixed micelles (Xi(m)). Mixing nonideality was expressed in terms of the molecular interaction parameter (beta12) as determined using the theory of Holland and Rubingh. Finally, the molecular thermodynamic model for mixed surfactant systems developed by Puvvada and Blankschtein was used to estimate the micellization free energy (DeltaGM) and to evaluate the synergistic phenomenon.

Novel catalytic effects in ester aminolysis in chlorobenzene

The mechanism of glyme catalyzed ester aminolysis in chlorobenzene should be modified by including a new reaction pathway that shows a first-order dependence on the concentration of the phase transfer catalyst and a second-order dependence on butylamine.

Influence of anionic surfactants on the electric percolation of AOT/isooctane/water microemulsions

A study was carried out concerning the influence of sodium alkyl sulfonates on the electric percolation of AOT/isooctane/water microemulsions ([AOT] = 0.5 M and W = [H2O]/[AOT] = 22.2). An important effect was observed with regard to the percolation temperature caused by the addition of small quantities of alkyl sulfonates (rho = [alkyl sulfonate]/[AOT] = 0.01). The short chain alkyl sulfonates (C3-C5) cause an increase in the percolation temperature, which in turn is reduced as we increase the chain length of the additive until we obtain a percolation temperature which is lower than that which is observed in the absence of an additive (C6-C8). For hydrocarbon chains of a greater length we can observe a new increase in the percolation temperature (C10-C18). This behavior has been explained as a consequence of (i) the incorporation of the additives at the interphase of the microemulsion and (ii) the geometric parameters of the different surfactants added to the microemulsion.

Basic hydrolysis of crystal violet in beta-cyclodextrin/surfactant mixed systems

The basic hydrolysis of crystal violet (CV) in mixed systems consisting of beta-cyclodextrin (beta-CD) and a micelle-forming surfactant, cetyltrimethylammonium chloride (CTACl), has been studied. beta-CD was found to catalyze the basic hydrolysis of CV through the interaction of its hydroxyl group, in its deprotonated form, with the carbocation in the complexed substrate. The addition of small amounts of CTACl, with [CTACl] below the critical micelle concentration, to beta-CD solutions does not have an effect upon the observed rate constant for the basic hydrolysis of CV. This behavior is different from that observed for the alkaline hydrolysis of N-methyl-N-nitroso-p-toluenesulfonamide and nitrophenyl acetates in mixed beta-CD/cationic surfactant systems. The proposed mechanism allows us to explain the experimental results on the basis of the high percentage of uncomplexed beta-CD in equilibrium with the micellar system, the low CV concentration, and the high value for the binding constant of CV by beta-CD.

Enhancement of copper and cadmium adsorption on kaolin by the presence of humic acids

The competitive adsorption equilibrium isotherms of Cu2+ and Cd2+ on kaolin have been measured at 298 K, in the presence and the absence of humic acids (HAs). HAs were found to enhance the metal adsorption capacity of mineral surfaces, in particular kaolin. This enhancement was also observed in the competitive adsorption of copper and cadmium on kaolin and kaolin-HA complex. This competitive adsorption shows that the presence of Cd2+ has not an important effect on Cu2+ adsorption, whereas a dramatic decrease is observed on the adsorption of Cd2+ in the presence of Cu2+. The Freundlich isotherm equation was found to provide an excellent fit to the experimental data. These results were compared with the independent adsorption of both heavy metals.