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The appealing properties of surfactant-intercalated Montmorillonites (Organo-montmorillonite, OMt) were successfully investigated to propose an effective drug delivery system for metronidazole (MNE) antibiotic therapy. This represents a serious pharmaceutical concern due to the adverse drug reactions and the low targeting ability of MNE. The non-ionic surfactant Tween 20 was used to functionalize montmorillonite, thus accomplishing the two-fold objective of enhancing the stability of clay dispersion and better controlling drug uptake and release. The adsorption process was performed under different experimental conditions and investigated by constructing the adsorption isotherms through high-performance liquid chromatography (HPLC) measurements. Powder X-ray diffraction (XRD) measurements were performed to characterize the MNE/OMt compounds. The gathered results revealed that the uptake of the drug occurs preferentially in the clay interlayer, and it is governed by positive cooperative processes. The presence of surfactant drives the adsorption into clay interlayer and hampers the adsorption onto external lamella faces. The good performances of the prepared OMt in the controlled release of the MNE were proved by investigating the release profiles under physiological conditions, simulating oral drug administration. Cytotoxicity measurements demonstrated the biocompatibility of the complexes and evidenced that, under specific experimental conditions, nanodevices are more biocompatible than a free drug.

The present work addresses the potential of different adsorbents for the recovery of the phlorotannin fraction present in the liquid phase from the autohydrolysis of Sargassum muticum. Operating with the extract generated during autohydrolysis of alginate exhausted algae, the kinetics followed pseudo-second order and the equilibrium corresponded to Freundlich model. In batch configuration, up to 70% phlorotannins were adsorbed and up to 30% were desorbed with ethanolic solutions. Comparable performance was observed with the autohydrolysis extracts from the whole algae. The phloroglucinol content, the reducing and ABTS antiradical capacities of the desorbed product increased by 2–4 times in relation to the values in the autohydrolysis extracts. Dynamic elution with 68% ethanol allowed 80% desorption and provided a concentrated extract with antiradical capacity equivalent to 1 g Trolox/g extract. This product showed anti-proliferative properties against lung adenocarcinoma A549 cells and against colon carcinoma HCT-116 cells. It also inhibited the production of reactive oxygen species by human neutrophils and inhibited prostaglandin E2 production via cyclooxygenase-2 in human whole blood.

We studied the effect of anionic, cationic, and nonionic surfactants on the interfacial tension between the two phases of the isobutyric acid/water system using spinning drop tensiometry. It has been found that interfacial tension decreases with increasing concentration of the surfactant in the case of sodium dodecyl sulfate (SDS) and of dodecyltrimethylammonium chloride (DTAC). However, in the case of Triton X-100 an increase of surfactant concentration leads to an increase of the interfacial tension. Such results are consistent with the upper critical solution temperature (UCST) in the presence of these surfactants: the UCST decreases with increasing SDS and DTAC concentrations while it increases in the case of Triton X-100. This apparently anomalous effect has been explained by considering the molecular structure of Triton X-100, which possesses a short polymeric chain that promotes its partitioning toward one of the two phases making them less compatible and thus raises the UCST and the interfacial tension.

The suitability of porous materials to immobilize and release under control bioactive molecules prompted us to design and study delivery systems of Vitamin A (VitA). This molecule, relevant in several physiological functions, is easily oxidized. Commercial VitA was immobilized in two different clays, montmorillonite K-10 (MMT) and sepiolite (SEP), and in MCM-41, by impregnation. Characterization of the resulting hybrid materials by XRD, FTIR and 13C and 29Si (MAS) NMR spectroscopies revealed its presence. The photo-stability tests showed decreased degradation of VitA in the clays, compared to MCM-41 and the pure VitA, while thermostability is observed until ∼100 °C. The kinetics of the release depended on the structural features of the support material and the pH. Sepiolite originated a classic profile of increasing amount of VitA with time, indicating that no oxidation was taking place. In both montmorillonite and MCM-41 the amount of released VitA dropped after ∼2 hours, reflecting oxidation. Oxidation and degradation products obtained when VitA was immobilized in MCM-41, both under nitrogen and in air, were identified by mass spectrometry experiments. Sepiolite is therefore a suitable material to use in controlled release of VitA, since it appears to prevent oxidation.

The main objectives of the present paper were the preparation and characterization of new surfactant-modified clays and the evaluation of their potential applicability as drug delivery systems for the oral administration of the cinnamic acid (CA) drug. The organoclays (OC) were prepared by loading different amounts of the biocompatible nonionic polyoxyethylene sorbitan monolaurate surfactant (Tween20) onto K10 montmorillonite (Mt) clay and characterized through the construction of the adsorption isotherms by means of the spectrophotometric method. The performance of the prepared material was verified by gathering the adsorption isotherms of the cinnamic acid onto the Mt/Tween20 organoclay and by monitoring the release profiles in both simulated gastric (SGF) and intestinal fluids (SIF). The quantitative analysis of the adsorption isotherms revealed that the uptake of the aromatic component onto both the blank and Tween20-loaded Mt was governed by positive cooperative processes and that the presence of the bio-surfactant enhanced the loading efficiency of the clay. By relating the raw montmorillonite uptake capability with that of the OC it was assessed that the presence of the bio-surfactant enhanced about 2 times the loading efficiency of the clay. From the XRD characterization of the obtained complexes, the successful intercalation of the drug into the prepared organoclay was demonstrated. Very useful information was obtained by the in vitro release studies, which showed that the release of the drug from both the clay and organoclay was prolonged in comparison with the pharmacokinetics of the free drug. Besides, the intercalation of the surfactant into the nano-carrier ensured the complete release of the CA after oral drug administration and the kinetics of the release process was strongly dependent on the type of drug formulation used, which means that the CA release can be modulated by properly functionalizing the clay surface.

We studied thermal frontal polymerization using a re-dox systeminan attempt to lower the temperature of thefrontallypolymerizable system while increasing the front velocity so as toobtain a self-sustaining front in a thinner layer than without theredox components. A cobalt-containing polymer with a meltingpoint of 63 C (Intelimer 6050X11) and cumene hydroperoxidewere used with a triacrylate. The use of the Intelimer decreasedthe front velocity but allowed fronts to propagate in thinner layersand with more filler while still having a pot life of days. Nonplanarmodes of propagation occurred. Fronts propagated faster when6-O-palmitoyl- L -ascorbic acid was used as a reductant. Interest-ingly, fronts were also faster with the reductant even without theIntelimer if kaolin clay was the filler; however, the pot life was sig-nificantly reduced. V C 2012 Wiley Periodicals, Inc. J Polym Sci PartA: Polym Chem 50: 2337–2343, 2012 KEYWORDS: acrylate; addition polymerization; frontal polymer-ization; kinetics; radical polymerization; redox polymersINTRODUCTION

An efficient protocol, based on advanced statistical diagnostics and robust fitting techniques applied to the least-squares processing of kinetic data of chemical reactions, is presented and discussed. The procedure, which is aimed at obtaining highly accurate estimation of the fitting parameters, consists of the identification of the outliers that remarkably impair the fitting by means of the so-called “leverage analysis” and some related diagnostics. This approach allows the elimination of the actually aberrant observations from the data set and/or their robust weighting to inhibit the negative effects induced on the data fitting, with consequent reduction of the bias introduced into the parameter estimates. It has been found that the proposed procedure, applied to experimental kinetic data, does yield to a significant improvement in the regression results. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 587–607, 2010

The Belousov–Zhabotinsky (BZ) reaction is the best known example of far from equilibrium self-organizing chemical reaction. Among the many dynamical behaviors that this reaction can exhibit, spatio-temporal chaos attracted particular interest, both for the ferroin and cerium catalyzed systems. In recent years transient chaos was found in the cerium catalyzed BZ reaction, when conducted in batch and unstirred reactors. It was established that the chaotic oscillations, originated by the coupling among chemical kinetics and transport phenomena, appeared and disappeared following a Ruelle–Takens–Newhouse scenario. In this Letter, we show results about the ferroin catalyzed system conducted in batch and unstirred reactors. An aperiodic transient regime was detected and we show that this is a genuine manifestation of spatio-temporal chaos.

The binding of the [(pentamethylcyclopentadienyl) (2,2′-bipyridyl)(aquo)rhodium(III)] complex [Cp*RhIII(bpy)H2O]2+, to l -α-dipalmitoylphosphatidyl choline (DPPC) vesicles has been estimated by studying the kinetics of the electron transfer reaction between the rhodium(III) complex and formiate ions. Kinetic measurements carried out under anaerobic conditions in absence and presence of DPPC show that the total reaction is composed of two steps. The rate of the first reaction increases with the phospholipid concentration, while that of the second process is independent of the concentration of DPPC. This is consistent with a reaction, where the two reacting species are partitioned between the aqueous and the vesicular pseudo-phases. The determined binding constants of [Cp*RhIII(bpy)H2O]2+ and formiate to the DPPC bilayers suggest that the palisade layer and the phospholipid head-group region of the DPPC vesicles are the respective solubilization sites.

The present study was aimed at the preparation and characterization of tailor made hybrid materials, whose peculiar hosting capability could be exploited in biotechnological applications. With this purpose, the modification of K10 montmorillonite by intercalation of Tween 20 surfactant, was accomplished. The influence of two internal parameters, namely pH and surfactant/clay ratio, on the surfactant uptake ability by clay was investigated. The adsorption mechanism was elucidated on the basis of complementary kinetic and equilibrium studies and, then, corroborated by the useful information provided by the FT-IR, TGA and XRD characterization. The gathered results allow to draw the conclusion that the whole surfactant uptake is the result of two contributions: a site-limiting component, governed by negative cooperative interactions, which takes into account for the Tween 20 adsorption onto the pristine clay, and a non-specific linear partitioning component, related to the adsorption of the surfactant onto the in situ prepared organo-clay. Moreover, at strongly acidic pH, a mechanism consisting of two-steps pathways involving two non-energetically equivalent binding sites of the clay surfaces, was proposed, while, on increasing the pH, the clay interlayer becomes the sole available site for the surfactant uptake. In the light of the interesting results obtained, among the plethora of potential biotechnological applications, the present paper suggests the exploitation of the prepared organo-clays to improve the performance of either hydrophilic or hydrophobic drug carriers systems.

The self-aggregation and solubilization capability of a series of amphiphilic copolymers obtained by derivatisation of polymeric chain of α,β-poly(N-2-hydroxyethyl)- dl -aspartamide (PHEA) with polyethylene glycols (PEG, being different molecular weight 2000 or 5000 Da, PEG2000 and PEG5000, respectively) and/or hexadecylamine alkyl chain (C16), namely PHEA–PEG2000, PHEA–PEG5000, PHEA–C16, PHEA–PEG2000–C16 and PHEA–PEG5000–C16, have been evidenced by performing systematic tensiometric and spectrophotometric studies. All measurements have been performed at 25.0 °C over a wide copolymer concentration range. The tensiometric results have shown that, for all copolymers studied, the surface tension of the copolymer aqueous solutions significantly depends on both concentration and copolymer nature and, in particular, copolymers bearing both the hydrophilic and hydrophobic moieties PEG and C16 alkyl chain, respectively, are much more surface active than those carrying only the PEG units and are able to self-aggregate. In addition, the hydrophilic portion plays a relevant role in the self aggregation process, in fact, the critical aggregation concentration values of the copolymers significantly increase on increasing molecular weight of PEG units in the copolymers. The spectrophotometric data have evidenced that all the copolymers exert a solubilization capability towards a sparingly water soluble drug, namely Tamoxifen (TAM), which extent depends on the copolymer concentration, copolymer nature and experimental procedure used. In fact, the amount of TAM solubilized significantly increases on increasing copolymer concentration. The drug is better solubilized by the PHEA–C16 copolymer and the solubilization capability decreases following the order PHEA–C16 > PHEA–PEG5000–C16 > PHEA–PEG2000–C16 > PHEA–PEG5000 > PHEA–PEG2000. The presence of the C16 moiety in the PHEA backbone leads to a solubilization ability which is roughly two times higher than that of copolymers bringing only the PEG chain. Moreover, the solubilization capability exerted by the copolymers is higher when the TAM is incorporated into the micelles during the micellization process with respect to that obtained when the drug is added to solutions containing pre-formed polymeric micelles. This trend suggests that the penetration of the drug molecules into the pre-formed micelles is hampered by the steric barrier constituted by the extended hydrophilic shell of the micelle. Further spectrophotometric results have evidenced that the drug loaded micelles are decidedly stable to dilution.

The solubilization site of 5,10,15,20-tetrakis-(2,6-dichlorophenyl)-porphyrin-Mn(III) (MnTDPPC) in l -α-dipalmitoylphosphatidyl choline (DPPC) vesicles was determined in a systematic UV–vis spectrophotometric study. Measurements of the MnTDPPC absorbance have been conducted at constant temperatures (in the interval 30 °C ≤ T ≤ 48 °C) and varying concentrations of phospholipid. In the entire temperature range, the absorption due to MnTDCCP was found to increase with increasing DPPC concentration, until it reaches a plateau value. The data have been analyzed using a pseudo-phase model yielding the binding constant of MnTDCPP to vesicular aggregates. No significant temperature dependence of the partition coefficient of MnTDCPP between the aqueous phase and the lipophilic domain of DPPC vesicles could be detected in the studied temperature interval (which also includes the main transition temperature of DPPC double layers, Tm = 41.3 °C), unambiguously indicating that MnTDCPP is confined in the palisade layer of DPPC bilayers. The nature of the interactions between the different reaction components have been investigated by tensiometric measurements, which provide further support for hydrophobic interaction between MnTDCPP and the DPPC vesicles. This solubilization locus makes this porphyrin – which is used as an important compound in biomimetic models for the cytochrome P450 model systems – accessible for electron donation by suitable, water soluble electron donors.

Rate data for the alkaline hydrolysis of the chloropentaamminecobalt(III) cation in the presence of mixed micelles composed of (i) anionic sodium decylsulphate (SDeS) and non-ionic dodecylpenta(oxyethylene glycol) monoether (C 12 E 5 ) surfactants and (ii) anionic sodium perfluorooctanoate (SPFO) and non-ionic C 12 E 5 surfactants has been obtained at T 298 K and constant electrolyte concentration 0.08 mol dm −3 ([NaOH] = 0.01 mol dm −3 , [NaClO 4 ] = 0.07 mol dm −3 ) over a wide range of total surfactant concentration ( C t ) and anionic mole fraction ( χ ). The critical micelle concentrations (c.m.c.s) of the mixed micelles have been determined over the entire χ range by means of surface tension measurements. The experimental data have been analyzed by the regular solution model for non-ideal mixing. The estimated negative values of the interaction parameter β indicate that attractive interactions between the two types of surfactants in the mixed anionic/non-ionic micelles take place. The kinetic data have shown that, at all mole fraction examined, at surfactant concentrations below the critical micelle concentration the rate constant values are not significantly influenced by the presence of surfactants while beyond the c.m.c. value, in all cases examined, the rate constant is conspicuously inhibited. The reaction rates decrease with increasing C t (at constant χ ) and χ (at constant C t ) to an extent which depends on the nature of the anionic surfactant used, i.e., the hydrogenated anionic surfactant is much more effective in inhibiting the hydrolysis process than the fluorinated one. The kinetic data, interpreted quantitatively by applying the pseudo-phase ion exchange model, indicate that two reaction paths contribute to the overall hydrolysis rate and that the binding constant of the complex ( K M ) decreases markedly as χ decreases. These findings have been attributed to the reduction of the charge density at the mixed micellar surface. Moreover, the K M values indicate that the capacity of the hydrogenated anionic micelles to bind the cobalt complex is higher than that of the fluorinated anionic micelle-forming surfactant. The present findings have been compared with those previously obtained concerning the effects of other aggregated systems upon the rate of the same hydrolysis reaction.

The incorporation of the bidentate ligand pyridine-2-azo-p-dimethylaniline (PADA) into micellar aggregates of the dimeric cationic surfactants propanediyl-, hexanediyl- and dodecanediyl-alpha,omega-bis(dimethylcetylammonium nitrate) (16-3-16,2NO(3)(-), 16-6-16,2NO(3)(-) and 16-12-16,2NO(3)(-), respectively) has been studied at 25 degreesC by examining the kinetics of the complexation reaction of the Ni(II) ion with this ligand. For comparison, cetyltrimethylammonium nitrate ( CTAN), which can be considered as the "monomeric'' surfactant of 16-3-16,2NO(3)(-), has also been used. The kinetic data have shown that, for 16-3-16,2NO(3)(-) and CTAN, at a surfactant concentration below the critical micelle concentration (cmc) the rate of the complex formation reaction does not significantly depend on the surfactant concentration, while it slightly decreases in the presence of the other two gemini surfactants. Beyond this critical value, in all cases examined, the rate constant is conspicuously inhibited by the presence of surfactant. The results below the cmc have been explained in the light of conductometric measurements, which have evidenced that both 16-6-16,2NO(3)(-) and 16-12-16,2NO(3)(-) form premicellar aggregates while 16-3-16,2NO(3)(-) and CTAN do not. The kinetic data above the cmc conform to a reaction mechanism that implies partitioning of the ligand only between the aqueous and the micellar pseudo-phases. The quantitative analysis of the kinetic data allows us to estimate the binding of PADA to the cationic micellar aggregates used. Solubilization of PADA in the micelles markedly depends on the nature of the surfactant used and, in particular, decreases on either increasing the spacer chain length or changing the surfactant type, namely conventional or gemini. These trends have been ascribed to the change in the shape of the micellar aggregates and, consequently, the hydrophobic character of the micelles, which can be modulated either by insertion of the spacer in the micellar interior or by using a conventional surfactant. The incremental free energy of transfer of a methylene group in the spacer chain from the aqueous to the micellar pseudo-phase has also been determined. The present data evidence that binding of PADA to micellar aggregates is primarily governed by hydrophobic interactions and the solubilization capability of gemini aggregates is superior to that of conventional micelles.

The dynamics of the Ce(IV)-catalyzed Belousov-Zhabotinsky (BZ) system has been spectrophotometrically monitored at 20.0 °C in unstirred batch conditions by using cuvettes with different geometry. The cuvette path length has been varied from 1 to 0.02 cm. The experimental results have shown that when the cuvette path length is in the range 1-0.05 cm the BZ system exhibits a chaotic behavior while below the critical value of 0.05 cm the dynamics of the BZ system is periodic. These trends have been ascribed to the elimination of the convective effect below a critical threshold and unambiguously demonstrate that convection is a bifurcation parameter for the route to chaos.

UV-vis-spectra evolution of Nile Red loaded into Tween 20 micelles with pH and [Tween 20] have been analysed in a non-conventional manner by exploiting the deconvolution method. The number of buried sub-bands has been found to depend on both pH and bio-surfactant concentration, whose positions have been associated to Nile Red confined in aqueous solution and in the three micellar solubilisation sites. For the first time, by using an extended classical two-pseudo-phases-model, the robust treatment of the spectrophotometric data allows the estimation of Nile Red binding constant to the available loci. Hosting capability towards Nile Red is exalted by the pH enhancement. Comparison between binding constant values classically evaluated and those estimated by the deconvolution protocol unveiled that overall binding values perfectly match with the mean values of the local binding sites. This result suggests that deconvolution procedure provides more precise and reliable values, which are more representative of drug confinement.

Systematic kinetic and equilibrium studies on the lead ions removal ability by Ca-alginate gel beads have been performed by varying several internal parameters, namely, number of gel beads, nature and composition of the ionic medium and pH, which allowed us to model a wastewater in order to closely reproduce the composition of a real sample. Moreover, the effects brought about the different ionic species present in the reacting medium have been evaluated. Differential Pulse Anodic Stripping Voltammetry (DP-ASV), has been systematically used to perform kinetic and equilibrium measurements over continuous time in a wide range of concentration. Kinetic and equilibrium data have been quantitatively analyzed by means of robust approach both for the non-linear regression and the subsequent residuals analysis in order to significantly improve the results in terms of precision and accuracy. Alginate gel beads have been characterized by SEM and an investigation on their swelling behavior has also been made. Removal efficiency of the calcium-alginate gel beads has been calculated and results obtained have showed a relevant dependence on ionic strength, composition of ionic media, pH of solution and number of gel beads. The number of gel beads takes part as key crucial components, i.e., the higher the number of beads the greater the amount of Pb(II) species removed from the sample, the lower the time needed to reach the maximum removal efficiency of 90%.

The adsorption profiles of the antibiotic metronidazole (MNE) into the K10-montmorillonite (MMT-K10) clay and the subsequent release have been investigated as a function of pH and MNE/MMT-K10 ratio, in order to evaluate the potential of the MNE/MMT-K10 hybrids as controlled drug delivery system. The adsorption mechanism has been first elucidated by performing complementary equilibrium and kinetic studies and through the X-ray diffractometry (XRD) characterization of the obtained composite materials. The gathered results allowed us to propose a mechanism consisting of a multi-step pathway involving the neutral and the cationic form of the drug, which interact with different sites of the clay surfaces, i.e. the interlayer region and the faces of the lamella. In a second step the drug release kinetics has been studied under physiological pH mimicking conditions simulating the oral drug administration and delivery. For the sake of comparison the commercial formulation has also been employed for the release studies. The investigation of the release profiles and the comparison with the commercial formulation of the drug reveal that the new-tailor made formulation could be fruitful exploited for successfully prolonged the action of drug in the desired site.

Complementary kinetic and equilibrium studies on the solubilization process of the sparingly water soluble tamoxifen (TAM) drug in polymeric aqueous solutions have been performed by using the spectrophotometric method. In particular, the amphiphilic copolymers obtained by derivatization of polymeric chain of poly(N-2-hydroxyethyl)-dl-aspartamide, PHEA, with poly(ethylene glycol)s, PEG (2000 or 5000 Da), and/or hexadecylamine chain, C16, namely PHEA-PEG2000-C16, PHEA-PEG5000-C16, PHEA-C16, have been employed. Preliminary to the kinetic and equilibrium data quantitative treatment, the molar absorption coefficient of TAM in polymeric micelle aqueous solution has been determined. By these studies the solubization sites of TAM into the polymeric micelles have been determined and the solubilization mechanism has been elucidated through a nonconventional approach by considering the TAM partitioned between three pseudophases, i.e., the aqueous pseudophase, the hydrophilic corona, and the hydrophobic core. The simultaneous solution of the rate laws associated with each step of the proposed mechanism allowed the calculation of the rate constants associated with the involved processes, the values of which are independent of both the copolymer concentration and nature, with the exception of the rate of the TAM transfer from the corona to the core. This has been attributed to the steric barrier, represented by the corona, which hampers the solubilization into the core. The binding constant values of the TAM to the hydrophilic corona of the polymeric micelles, calculated through the quantitative analysis of the equilibrium data, depend on the thickness of the hydrophilic headgroup, while those of the hydrophobic core are almost independent of the copolymer type. Further confirmation to the proposed solubilization mechanism has been provided by performing the kinetic and equilibrium measurements in the presence of PHEA-PEG2000 and PHEA-PEG5000 copolymers.

Rate constants for the mononuclear rearrangement (MRH) of Z -phenylhydrazones of some 5-substituted-3-benzoyl-1,2,4-oxadiazoles in water have been measured in the presence of zwitterionic micelles. The use of micellized N -tetradecyl- N , N -dimethylamineoxide (C 14 DMAO) as the reaction medium allowed to solubilize the otherwise water-insoluble oxadiazoles. Micellar rate effects were analyzed by using a simple pseudo-phase model and compared with those obtained in non-ionic micelles (Triton X-100). Evidence that both the rate of the rearrangement reaction and the binding of the substrates to the micelles are mainly governed by substrate hydrophobicity is obtained. The disagreement with the primarily sterically controlled MRH in Triton X-100 micelles highlights large and intriguing differences between the two micellar environments.

The kinetic of the adsorption of two nucleic acid bases, namely adenine (A) and cytosine (C), on K10 montmorillonite (MMT) clay has been investigated over a wide range of nitrogenous bases concentrations, by using the spectrophotometric method. The measurements have been performed at T = 25.0 °C and pH = 4.0 where adenine and cytosine exist both in their protonated and neutral forms. Preliminary to the kinetic data treatment, the adsorption isotherms have been gathered and, then, analyzed by using the Freundlich and the Dubinin–Radushkevich model. The obtained results allow to draw the conclusion that physisorption of adenine and cytosine on MMT occurs and the process is mainly governed by weak interactions. Different kinetics models have been applied to analyze the kinetic data and the discrimination has been performed by means of various statistics. It has been found that for both A and C the adsorption kinetics follow a double exponential model (DEM), corresponding to two parallel steps involving the cationic and the neutral species which interact with different sites of the clay surface, i.e., the interlayer region and the faces of the lamella. The kinetic constant values associated to the proposed pathways are independent of the nitrogenous bases' concentrations and the nucleic acid bases' nature. The mechanism, proposed in the light of the equilibrium data, has been corroborated by performing kinetic measurements at pH = 2.0 and pH = 6.0 where A and C exist only in their protonated form and neutral form, respectively.

The transition from planar fronts, trigger waves or solitary pulses to spirals in excitable media, has attracted increasing interest in the past few decades, mainly because of its relevance for biological and medical applications. In this paper we describe a new and convenient method for spiral generation starting from symmetric wavefronts. By using the micelle-forming zwitterionic surfactant N-tetradecyl- N,N-dimethylamine oxide in a Belousov–Zhabotinsky solution, it is possible to control to a large extent the domains where spirals can be spontaneously generated. The mechanism responsible for the wavefront break up lies in the interaction of the propagating waves with the unexcitable regions formed by the interaction of the surfactant with some of the Belousov–Zhabotinsky key intermediates.

In the present study, the role played by the reactants concentration on the nonlinear response of a Belousov–Zhabotinsky (BZ) system to the addition of a self-assembling non-ionic polymer, poly(ethylene glycol) (PEG), has been assessed. The oscillatory parameters are influenced to an extent that significantly depends on the concentration of both the polymer and the Belousov–Zhabotinsky components. The effects obtained were attributed to the reaction among some of the BZ key species and the backbone and the alcoholic functional groups of the polymer, both in its monomeric and aggregated forms. Support to the proposed perturbation mechanism has been provided by performing numerical simulations with the MBM model and by characterizing the physicochemical behavior of the PEG aqueous solution by means of viscosimetric and spectrofluorimetric measurements.

Chemical oscillations generated by the Belousov–Zhabotinsky reaction in batch unstirred reactors, show a characteristic chaotic transient in their dynamical regime, which is generally found between two periodic regions. Chemical chaos starts and finishes by following a direct and an inverse Ruelle–Takens–Newhouse scenario, respectively. In previous works we showed, both experimentally and theoretically, that the complex oscillations are generated by the coupling among the nonlinear kinetics and the transport phenomena, the latter due to concentration and density gradients. In particular, convection was found to play a fundamental role. In this paper, we develop a reaction–diffusion–convection model to explore the influence of the reagents consumption (BrO−3 in particular) in the inverse transition from chaos to periodicity. We demonstrated that, on the route towards thermodynamic equilibrium, the reagents concentration directly modulates the strength of the coupling between chemical kinetics and mass transport phenomena. An effective sequential decoupling (reaction–diffusion–convection → reaction–diffusion → reaction) takes place upon the reagents consumption and this is at the basis of the transition from chaos to periodicity.

The kinetics of the oxidation of malonic acid and (its substituted compounds, methyl-, ethyl-, butyl- and benzyl-malonic acid) by ceric ions has been studied at 20.0 °C in the absence and the presence of the surfactant N-tetradecyl-N,N-dimethylamine oxide (C 14 DMAO). The addition of increasing amounts of C 14 DMAO influences the rate of the redox process to an extent that significantly depends on the hydrophobicity of the reducing species. The reactivity data together with the estimated binding constants and the standard transfer free energies of the malonic acids from water to the micelles suggest that the malonic acid is confined to the aqueous pseudo-phase while for the other solutes the binding occurs in the palisade layer of micelles.

The solubilization site of indicaxanthin (Ind) in lipid bilayers was investigated by the kinetics of Ind oxidation by peroxyl radicals in water and in aqueous/L-alpha-dipalmitoyl-phosphatidylcholine (DPPC) vesicles, pH 7.4, and 37.0 and 48.0 degrees C, that is, in a gel-like and a crystal liquidlike bilayer state, respectively. The time-dependent Ind absorbance decay, matched with a successful simulation of the reaction kinetic mechanism by Gepasi software, supported a multistep pathway. Computer-assisted analysis allowed calculation of the rate constants associated with the reactions involved, the values of which decreased with increasing DPPC concentration. The binding constant calculated according to a pseudo two-phase distribution model did not vary with the physicochemical state of the vesicle, indicating location of Ind in a region whose state is not affected by temperature changes, at the interface between hydrophobic core and hydrophilic head groups. Other measurements carried out in the presence of dimyristoyl-phosphatidylcholine vesicles, indicated that the phytochemical was confined to the aqueous phase.

Far-from-equillibrium oscillating chemical reactions are among the simplest systems showing complex behaviors and emergent properties. This class of reactions is often employed to mimic and understand the mechanisms of a great variety of biological processes. In this context, pattern formation due to the coupling between reaction and transport phenomena represent an active and promising research area. In this paper, we present results coming from experiments where we tried to blend the structural properties of self-assembled matrixes (sodium dodecyl sulphate micelles and phospholipid bilayers) together with the evolutive peculiarities of the Belousov–Zhabotinsky reaction. A series of interesting dynamical behaviors, like spatio-temporal chaos, stationary patterns and segmented waves, were found in reaction–diffusion and reaction–diffusion–convection experiments.

The effects of the anionic surfactant sodium dodecyl sulfate (SDS) on the spatio-temporal and temporal dynamics of the ferroin-catalyzed Belousov-Zhabotinsky (BZ) reaction have been studied over a wide surfactant concentration range. For the first time, investigations were performed also for unstirred systems. The presence of SDS in the reaction mixture influences the oscillatory parameters to an extent that significantly depends on the surfactant concentration. The trend of the wave speed v upon the increasing amount of SDS was found to have a maximum at [SDS] = 0.075 mol dm (-3) ( v = 0.071 mm s (-1)), after which the speed decreased to 0.043 mm s (-1) at [SDS] = 0.5 mol dm (-3), which is below the value found in the absence of the surfactant ( v = 0.055 mm s (-1)). The response of the oscillatory BZ system to the addition of SDS has been ascribed to two different causes: (a) the peculiar capability of the organized surfactant assemblies to affect the reactivity by selectively sequestering some key reacting species and (b) the modifications induced by SDS on the physical properties of the medium. These hypotheses have been corroborated by performing spectrophotometric investigations on the stirred BZ system. Complementary viscosity measurements gave useful hints for the clarification of the surfactant role.

Interactions between reaction–diffusion systems and aggregated host environments are a subject of widespread interest. In this work, the behavior of the Belousov–Zhabotinsky reaction was investigated in a micellar environment formed by the zwitterionic surfactant N-tetradecyl-N,N-dimethylamine oxide (C14DMAO). The appearance of an induction period with a threshold-like dependence upon the surfactant concentration, was detected at [C14DMAO] = 5.0 × 10−3 mol dm−3. These new features were explained in terms of the segregation ability typical of the amphiphilic self-assembling systems. Numerical simulations were also performed to confirm the proposed mechanism.

The solubilization site of two betalain pigments, namely, betanin and indicaxantin, into l-alpha-dipalmitoyl-phosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) vesicles was investigated by a spectrophotometric study. Pigment absorbance was monitored by varying phospholipid concentration, at a constant temperature that was varied in a range including the main phase transition temperature (Tm) of the relevant phospholipid bilayer. Maximum betanin absorption increased with the increase of DPPC concentration within the entire temperature range, reaching a plateau. The binding constant (Kb) of the pigment, calculated according to a pseudo-two-phase model, varied with the temperature, indicating that betanin is located at the hydrophobic interior of the bilayer. Other measurements of binding of betanin to DMPC and of indicaxanthin to either DPPC or DMPC vesicles ruled out that these compounds were solubilized in the hydrophobic interior of these bilayers.

The response of the Belousov-Zhabotinsy (BZ) system to the addition of increasing amounts of the anionic surfactant sodium dodecyl sulfate (SDS) was monitored at 25.0 degrees C in stirred batch conditions. The presence of SDS in the reaction mixture influences the oscillatory parameters, i.e., induction period and oscillation period, to an extent that depends on the surfactant concentration. The experimental results have shown that the induction period increases slightly on increasing surfactant concentration and, then, a further increase in the [SDS] leads to an enhancement while the oscillation period increases monotonously on increasing SDS concentration. It has been proposed that the response of the oscillatory BZ system to the addition of SDS is due to the peculiar capability of the organized surfactant assemblies to affect the reactivity by selectively sequestering some key reacting species. Indeed, explanations of the experimental results have been given on the basis of the role played by the micellar shape, which in turn dictates the hydrophobic nature. The suggested perturbation effects have been supported by performing viscosity measurements on the aqueous SDS solutions and by the spectrophotometric estimation of the binding constant of the bromine species to the micellar aggregates. This study has indirectly corroborated the existence of two kind of micelles and unambiguously revealed that the bromine species show a different affinity toward the spherical and rod-like micelles.

The dynamic evolution of the oscillatory Belousov–Zhabotinsky reaction upon addition of increasing amount of the non-ionic polymer polypropylene glycol with molecular weight 425 g mol−1 (PPG-425) was investigated in a stirred-batch reactor by monitoring the Ce(IV) absorbance changes. The oscillatory parameters are significantly altered by the presence of the polymer. The findings obtained in the present work revealed that the PPG-425 is not only more effective, than other polymer previously [R. Lombardo, C. Sbriziolo, M.L. Turco Liveri, K. Pelle, M. Wittmann, Z. Noszticzius, in: J.A. Pojman, Q. Tran-Cong-Miyata (Eds.), Nonlinear Dynamics in Polymeric Systems, American Chemical Society, Washington, DC, 869 (2004) 292] studied, in perturbing the BZ systems but also more capable of producing key radical species, which in turn can be exploited for the preparation of new polymeric materials.

We report definitive evidence for an effective interfacial tension between two types of miscible fluids using spinning-drop tensiometry (SDT). Isobutyric acid (IBA) and water have an upper critical solution temperature (UCST) of 26.3 degrees C. We created a drop of the IBA-rich phase in the water-rich phase below the UCST and then increased the temperature above it. Long after the fluids have reached thermal equilibrium, the drop persists. By plotting the inverse of the drop radius cubed (r(-)(3)) vs the rotation rate squared (omega(2)), we confirmed that an interfacial tension exists and estimated its value. The transition between the miscible fluids remained sharp instead of becoming more diffuse, and the drop volume decreased with time. We observed droplet breakup via the Rayleigh-Tomotika instability above the UCST when the rotation rate was decreased by 80%, again demonstrating the existence of an effective interfacial tension. When pure IBA was injected into water above the UCST, drops formed inside the main drop even as the main drop decreased in volume with time. We also studied 1-butanol in water below the solubility limit. Effective interfacial tension values measured over time were practically constant, while the interface between the two phases remains sharp as the volume of the drop declines. The effective interfacial tension was found to be insensitive to changes in temperature and always larger than the equilibrium interfacial tension. Although these results may not apply to all miscible fluids, they clearly show that an effective interfacial tension can exist and be measured by SDT for some systems.

Nonionic Triton X-100 micelles solubilize the otherwise water-insoluble (Z)-phenylhydrazones of some 5-substituted 3-benzoyl-1,2,4-oxadiazoles to an extent suitable for studying the occurrence of a general-base-catalyzed rearrangement in the presence of borate buffers (pH 9.6). The kinetic data, obtained at 40.0 degrees C over a wide range of surfactant concentrations, are found to conform to a reaction scheme which implies partitioning of the substrates and the base between water and the micellar pseudophase. Evidence that both the rate of the rearrangement reactions and the binding of the substrates to the micellar aggregates are primarily governed by the steric requirements of the 5-substituent group is obtained. Copyright 2001 Academic Press.

A systematic study aimed at obtaining new organoclays for the treatment of Olive Mill Waste water (OMW) has been performed. Several organoclays have been prepared by loading different amounts of the biocompatible surfactant Tween20 onto the K10 montmorillonite (MMT). Complementary kinetic and equilibrium studies on the adsorption of the Tween20 onto the MMT have been carried out and the characterization of the new tailor-made bio-materials has been performed by means of the XRD and FT-IR measurements. Finally the prepared bio-organoclays have been successfully applied for the OMW remediation and they proved to be highly effective in decreasing the organic content (OC) to an extent that depends on both the amount of loaded surfactant and the experimental protocols applied.