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Several extraction methods are used to isolate natural compounds, and recent approaches utilize subcritical or supercritical extraction media. In this paper we compare extraction methods based on subcritical eluents, dimethyl ether (sC-DME) and n-butane (sC-nB), under mild conditions, using coffee beans and powder as an exemplary raw material. The parameters to be controlled to improve the extraction are considered, and the resulting data discussed. The results obtained display higher selectivity of sC-DME for caffeine (1.9%w/w sC-DME vs. 1.7%w/w sC-nB, on dry extract) and a good yield (0.479 mg/g of caffeine from green coffee beans) compared to, e.g., supercritical carbon dioxide (SC-CO2), which shows 0.32 mg/g of caffeine at higher pressure and temperature (25 MPa, 40 °C). We also discuss some technical implementations for optimizing the use of sub-critical eluents through proper combinations of pressure and temperature. We show that extraction processes based on sub-critical eluents are easy to operate and efficient, and can be easily automated.

A low-cost Transition Temperature Mixture (TTM) has been synthesized by mixing ethylene glycol and potassium hydroxide as a new non-aqueous CO2 sorbent. Boric acid has been added to ensure the reversibility of the system and a small amount of water to modulate the viscosity and optimize the performances. The resulting mixtures have been characterized in terms of viscosity, conductivity and density over temperature (therefore ionicity via Walden plots) and the effect of temperature, pressure and the kinetics of the absorption have been evaluated. Under optimized conditions, the four-component mixture EG/KOH/BA/H2O 3:1:1:3 can absorb 24 gCO2/kgsorbent in 30 minutes at 35°C at 1 atm (59 after 4 h) and 60 gCO2/kgsorbent in 30 minutes at high pressure (10 and 20 atm, 80 gCO2/kgsorbent after 50 min), while the desorption is quantitative after 30 minutes at only 60°C under a gentle N2 flow. The system is robust enough to ensure multiple absorption/desorption cycles.

Gas hydrate formation usually occurs with a certain delay after a system composed of water and a hydrate-forming gas is put under suitable thermodynamic conditions of pressure and temperature. This delay period is called the “induction time”, and because of its large variability within a single experimental setting, hydrate formation is often referred to as a stochastic process. The evaluation of induction times, together with other measurements, is taken as an indication for the efficiency of hydrate inhibitors, and they are usually carried out by simply putting the experimental system under chosen P/T conditions and then waiting for the hydrate to form and measuring the time elapsed. In this paper, we present an improved procedure by which the variability of hydrate induction times can be remarkably reduced, while keeping a good correlation of measured induction times with the respective temperatures as obtained by a constant cooling method. In this procedure, temperatures are lowered by 0.5 °C after ea...

A low-cost Transition Temperature Mixture (TTM) has been synthesized by mixing ethylene glycol and potassium hydroxide as a new non-aqueous CO2 sorbent. Boric acid has been added to ensure the reversibility of the system and a small amount of water to modulate the viscosity and optimize the performances. The resulting mixtures have been characterized in terms of viscosity, conductivity and density over temperature (therefore ionicity via Walden plots) and the effect of temperature, pressure and the kinetics of the absorption have been evaluated. Under optimized conditions, the four-component mixture EG/KOH/BA/H2O 3:1:1:3 can absorb 24 gCO2/kgsorbent in 30 minutes at 35°C at 1 atm (59 after 4 h) and 60 gCO2/kgsorbent in 30 minutes at high pressure (10 and 20 atm, 80 gCO2/kgsorbent after 50 min), while the desorption is quantitative after 30 minutes at only 60°C under a gentle N2 flow. The system is robust enough to ensure multiple absorption/desorption cycles.

Stationary phases (SPs) based on silica matrices functionalized with amino groups linked to their surface through alkyl chains of various length have found remarkable success in performing HILIC separations, showing really effective resolution towards a wide typology of compounds of biological interest, such as carbohydrates, nucleosides, purine and pyrimidine bases. Recently, we developed an operationally simple procedure, named DNBA-M, non-destructive for the analysed SP, designed to quantify the density of basic groups (typically amino groups) chemically bonded to the surface of porous solids. In the present study the DNBA-M procedure has been suitably modified to allow the quantification of any typology of amino groups present on silica matrices packed into HPLC columns. The new approach, named OC-DNBA-M, has been successfully validated through analysis of two HPLC columns packed with aminopropyl-silica matrices. Afterwards, it was also demonstrated as the OC-DNBA-M procedure may allow the effective and in-depth analysis of the structural composition characterizing SPs packed inside HPLC columns, in which amino-groups have been differently and only partially involved in following ureidic functionalizations. It was also proved how the analysed columns can be readily re-employed for the chromatographic applications for which they have been designed, without appreciable deterioration of the respective discrimination abilities.

An amphiphilic calix[6]arene, alone or complexed with an axle to form a pseudo-rotaxane, has been embedded into liposomes prepared from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and the permeability of the membrane-doped liposomes towards Cl− ions has been evaluated by using lucigenin as the fluorescent probe. The pseudo-rotaxane promotes transmembrane transport of Cl− ions more than calix[6]arene does. Surprisingly, the quenching of lucigenin was very fast for liposomes doped with the positively charged axle alone. Molecular dynamics (MD) simulations and quantum-chemical calculations were also carried out for providing a semi-quantitative support to the experimental results.

A novel, rapid, simple graphene/Fe3O4 based dispersive magnetic solid phase extraction was developed for the simultaneous separation/preconcentration and determination of non steroidal anti-inflammatory drugs with ultra high performance liquid chromatography coupled with photodiode array detection. Several parameters influencing the extraction efficiency of the investigated analytes such as the extraction time, the amount of graphene/Fe3O4, the sample pH, the ionic strength and the elution solvent were evaluated and optimized. Under optimal conditions, the linearity was in the range of 0.002–25 μg/mL for furprofen, diclofenac and ketoprofen, 0.003–25 for flurbiprofen, naproxen and fenbufen, 0.004–25 for indoprofen with a good coefficient of determination (R2> 0.9991) for each analyte. The inter-and- intra day accuracy (BIAS%) for human plasma and urine ranged between −7.15% to 6.20% and −5.17% to 4.87%, respectively.The precision (RSD%) in human plasma and urine was less than 8.67% and 8.92%, respectively. The proposed method was applied to the determination of NSAIDs in human plasma and urine.

We have measured the diffusion coefficients, D, of aqueous micelles formed by cetyltriethyl-, cetyltripropyl- and cetyltributyl-ammonium bromides (CTEABr, CTPABr and CTBABr, respectively) and cetyltriethyl- and cetyltripropyl-ammonium hydroxides (CTEAOH and CTPAOH, respectively) by dynamic light scattering (DLS) at several temperatures from 15 to 55 °C and a range of surfactant (0.01–0.05 M) and salt (0.02–0.06 M NaBr; 0.05–0.3 M NaOH) concentrations. From values of D, we derived the respective fractional ionization values of micellar surfaces. For surfactants with bromide counterion we obtained fits of the diffusivity data using the linear interaction/DLVO approach, thus yielding estimates of the micellar hydrodynamic radius, Rh, and the micellar fractional ionization, α, which ranged from 0.26 to 0.35. For CTEAOH and CTPAOH, the fits appeared to be poorly sensitive to changes in the London-Van der Waals interactions, as expressed by the Hamaker constant, and only a large fractional ionization could account for the observed diffusivities.

Many biologically active compounds feature low solubility in aqueous media and, thus, poor bioavailability. The formation of the host-guest complex by using calixarene-based macrocycles (i.e., resorcinol-derived cyclic oligomers) with a good solubility profile can improve solubilization of hydrophobic drugs. Herein, we explore the ability of resorc[4]arenes to self-assemble in polar solutions, to form supramolecular aggregates, and to promote water-solubility of an isoflavone endowed with anti-cancer activity, namely Glabrescione B (GlaB). Accordingly, we synthesized several architectures featuring a different pattern of substitution on the upper rim including functional groups able to undergo acid dissociation (i.e., carboxyl and hydroxyl groups). The aggregation phenomenon of the amphiphilic resorc[4]arenes has been investigated in a THF/water solution by UV–visible spectroscopy, at different pH values. Based on their ionization properties, we demonstrated that the supramolecular assembly of resorc[4]arene-based systems can be modulated at given pH values, and thus promoting the solubility of GlaB.

The ability of some zwitterionic natural deep eutectic solvents (NADESs) based on N,N,N-trimethylglycine (TMG) and carboxylic acids (oxalic, glycolic and phenylacetic) to act as environmentally friendly solvents for CO2 capture has been investigated. The solubility of CO2 in the NADESs was measured gravimetrically at different temperatures in the range 298.15–333.15 K, and at different pressures in the range 0.1–4 MPa. The effect of the adopted experimental conditions has been discussed. The highest uptake has been observed for phenylacetic acid/TMG DES at 313.15 K and 4 MPa (45.5 mg CO2/g DES). The efficiency of this NADES as CO2 sorbent when reused in subsequent capture cycles has been evaluated. This work might open new perspectives in developing the most appropriate combination of HBA and HBD components of the DESs and the most appropriate operative conditions for an environmentally friendly CO2 capture.

(1) Background: The aim of this study was to optimize, through a cheap and facile protocol, the covalent functionalization of graphene oxide (GO)-decorated cortical membrane (Lamina&reg, ) in order to promote the adhesion, the growth and the osteogenic differentiation of DPSCs (Dental Pulp Stem Cells), (2) Methods: GO-coated Laminas were fully characterized by Scannsion Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) analyses. In vitro analyses of viability, membrane integrity and calcium phosphate deposition were performed, (3) Results: The GO-decorated Laminas demonstrated an increase in the roughness of Laminas, a reduction in toxicity and did not affect membrane integrity of DPSCs, and (4) Conclusions: The GO covalent functionalization of Laminas was effective and relatively easy to obtain. The homogeneous GO coating obtained favored the proliferation rate of DPSCs and the deposition of calcium phosphate.

Two calix[4]resorcinarenes, which differ in the length of the alkyl chain on the methylene bridge between the aromatic rings, have been embedded in unilamellar liposomes prepared from 1-palmitoyl-2-oleoyl-sn-glycerol-3-phosphocholine in three host/guest ratios, following two different procedures. The effect of the insertion of the guests has been evaluated through the measurements of the viscosity and the kinetic stability of the liposomal systems by means of the fluorescent probes pyrene and 5(6)-carboxyfluorescein. The presence of the guests reduces the viscosity of the liposomes, suggesting a modification of the bilayer structure. However, this does not affect liposome stability. A calix[4]resorcinarene cavitand with a more rigid conformation compared to the parent resorcinarene, has been also synthetized and embedded in liposomes. The free energy of the insertion of the substrates in the lipid bilayer has been evaluated through Molecular Dynamics simulations.

Nowadays solid materials in which amino groups are linked to silica matrices through alkyl chains of different length (C18, C8, C4) are successfully employed in CO2 capture and storage technologies, as well as in a variety of chromatographic applications. In particular, their use as stationary phases finds remarkable success in performing HILIC separations and, in general, in the effective resolution of important compound classes (e.g. mixtures of mono- or oligo-saccharides). In this study an original and operationally simple procedure designed to quantify the density of basic groups (typically amino groups) chemically bonded to the surface of porous solids, which also allows a full recovery of the analysed material, is presented. The method is based on the preventive acid-base reaction of the basic groups linked to the solid by 3,5-dinitrobenzoic acid (DNBA). The quantification of the basic functionalities is then performed by an UV-spectrophotometric retro-titration of the thus salified solid matrix (or, alternatively, by HPLC approach), resorting to a preventive either acid or basic displacement of DNBA from the matrix. The uncertainty of the density measurements is assessed by 13%.

The present comprehensive kinetic investigation in micellar systems deepens and broadens the knowledge of mononuclear rearrangement of heterocycles (MRH) of Z -phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole, reaction already carried out in different reaction media. As a matter of fact the use of four types of micelles different for charge, shape and polarity has allowed us to evaluate the role of micellar systems, as reaction media, on the rate of MRH and to quantify their catalytic effect. Moreover, the data obtained have enabled us to draw some intriguing conclusions on the localization of the substrate in the micelles, the transition state structure and the driving force of the reaction.

Chronic wounds represent an increasing problem worldwide. Graphene oxide (GO) has been reported to exhibit strong antibacterial activity toward both Gram-positive and Gram-negative bacteria. The aim of this work was to investigate the in vitro antimicrobial and antibiofilm efficacy of GO against wound pathogens. Staphylococcus aureus PECHA 10, Pseudomonas aeruginosa PECHA 4, and Candida albicans X3 clinical isolates were incubated with 50 mg/liter of GO for 2 and 24 h to evaluate the antimicrobial effect. Optical and atomic force microscopy images were performed to visualize the effect of GO on microbial cells. Moreover, the antibiofilm effect of GO was tested on biofilms, both in formation and mature. Compared to the respective time controls, GO significantly reduced the S. aureus growth both at 2 and 24 h in a time-dependent way, and it displayed a bacteriostatic effect in respect to the GO t = 0; an immediate (after 2 h) slowdown of bacterial growth was detected for P. aeruginosa , whereas a tardive effect (after 24 h) was recorded for C. albicans . Atomic force microscopy images showed the complete wrapping of S. aureus and C. albicans with GO sheets, which explains its antimicrobial activity. Moreover, significant inhibition of biofilm formation and a reduction of mature biofilm were recorded for each detected microorganism. The antibacterial and antibiofilm properties of GO against chronic wound microorganisms make it an interesting candidate to incorporate into wound bandages to treat and/or prevent microbial infections.

The potential application of some novel zwitterionic Natural Deep Eutectic Solvents, NADESs, based on betaine N,N,N-trimethylglycine and carboxylic acids (glycolic, phenylacetic and oxalic acid), has been evaluated in the synthesis of gold nanoparticles (AuNPs). AuNPs have been successfully obtained by reduction of gold(III) chloride trihydrate by ascorbic acid or sodium borohydride as reducing agents, without the use of any surfactant or capping agent. The effect of the different experimental conditions (nature of the reducing agent, temperature) has been discussed. In the NADES composed of trimethylglycine and oxalic acid, no addition of a reductant was needed because AuNPs start to form immediately after the dissolution of the precursor salt. This result may open new perspectives in fine-tuning smart solvent characteristics and developing the most appropriate NADES for an environmentally friendly metal nanoparticle synthesis without using auxiliary chemicals.

Equilibrium constants for the proton transfer reaction between pyridines and trifluoroacetic acid were measured in room-temperature ionic liquids (ILs) of different cation-anion compositions. The experimental equilibrium constants for ion-pair formation were corrected according to the Fuoss equation. The calculated equilibrium constants for the formation of free ions were taken as a quantitative measure of the base strength in IL solutions and compared with the relative constants in water. The effect of IL composition is discussed for a series of fixed IL anions and fixed IL cations. Finally, the sensitivity of the proton transfer reaction to the electronic effects of the substituent groups on the pyridine ring was quantified by applying the Hammett equation. A more marked levelling effect on the base strength was observed in ILs than in water. The Hammett reaction constants ρ were then correlated with solvent parameters according to a multi-parametric analysis, which showed that both specific hydrogen-bond donor/acceptor and non-specific interactions play an important role, with α and permittivity being the main parameters affecting the ability of the IL to differentiate the strength of the base.

Few-layer graphene aqueous dispersions are obtained by exploiting liposomes as effective exfoliating agents for graphite. Raman measurements evidence the presence of non-oxidized double layer graphene as well as amphiphilic phospholipid molecules organized in bilayers in the samples. TEM analyses confirmed that the obtained homogeneous graphene nanosheets are embedded in the liposomal bilayer. The as-prepared graphene aqueous dispersion is stable for days and demonstrates significant antibacterial activity against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) strains, with a reduction in the growth of S. aureus and E. coli as high as 60 and 78%, respectively.

Surfactants are amphiphilic molecules active at the surface/interface and able to self-assemble. Because of these properties, surfactants have been extensively used as detergents, emulsifiers, foaming agents, and wetting agents. New perspectives have been opened by the exploitation of surfactants for their capacity to interact as well with simple molecules or surfaces. This feature article gives an overview of significant contributions in the panorama of the current research on surfactants, partly accomplished as well by our research group. We look at several recent applications (e.g., adsorption to graphitic surfaces and interactions with hydrate crystals) with the eye of physical organic chemists. We demonstrate that, from the detailed investigation of the forces involved in the interactions with hydrophobic surfaces, it is possible to optimize the design of the surfactant that is able to form a stable and unbundled carbon nanotube dispersion as well as the best exfoliating agent for graphitic surfaces. By studying the effect of different surfactants on the capacity to favor or disfavor the formation of a gas hydrate, it is possible to highlight the main features that a surfactant should possess in order to be devoted to that specific application.

The kinetics of the thermal isomerization of some diastereomers of three chiral 1,3,4 thiadiazoline derivatives, selected as case studies of structures resulting from mono-alkyl substitution of the anancomeric 4-acetyl-2-acetamido-1,3,4-thiadiazolinyl-spiro-cyclohexane (TsC) framework, have been investigated in order to elucidate the possible mechanistic pathways and the structural factors responsible for the observed spiro-junction lability. The insertion of a methyl or a t-butyl group on the C2 or C3 position with respect to the spiro junction generates two stereogenic centres, so that two pairs of enantiomers exist. The first-order rate constants for the isomerization of the less stable enantiomers into the most stable ones have been measured in different solvents and at different temperatures through batch-wise kinetic determinations. The obtained data have been successfully rationalized by DFT calculations and Linear Solvation Energy Relationships (LSER) analyses. The achieved elucidation should make it possible to plan a more rational synthesis of this kind of pharmacologically active compounds, thus affording a practical tool that is useful for controlling the involved stereochemistry and spiro-junction lability.

The mechanism of base catalyzed keto-enol interconversion of aqueous 2-phenylacetylthiophene has been investigated by a joint application of experimental and computational approaches. Primarily we have focused our attention on the water-enolate proton transfer representing the rate determining step of the reaction. Computational results, in good agreement with experimental data demonstrate the crucial role exerted by the solvent. In particular, beyond the bulk catalytic effect an explicit assistance of solvent molecules allows the reaction to increase its efficiency. A combination on Molecular Dynamics simulations and Perturbed Matrix Method calculations also highlight the subtle balance between energetic and entropic effects which characterize the mechanistic scenario. (C) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: 1293-1305, 2011

The effect of entrapped beta-cyclodextrin (beta-CD) on the stability of multilamellar vesicles (MLVs) of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), prepared by the dehydration-rehydration method, was studied by monitoring the release of 5(6)-carboxyfluorescein encapsulated into the liposomes. Different hydrophobic guests, such as Fullerene C(60), have been incorporated into the POPC bilayer in order to modify the membrane composition. The kinetic results as well as ESI-MS measurements evidenced that the destabilizing activity of beta-CD is due to the formation of beta-CD inclusion complexes and the consequent removal of selected bilayer constituents from the liposomal membrane. Hence, when beta-CD was added to the liposomes in the form of a strong, water-soluble 2:1 beta-CD/C(60) inclusion complex, such a destabilizing effect was not observed. However, the same beta-CD/C(60) inclusion complex does not form as a result of C(60) extraction from the bilayer. This may be attributed either to the overwhelming concentration of POPC with respect to C(60) and/or to the fact that C(60) is largely aggregated in the bilayer. Turbidimetric and fluorimetric determinations of lamellarity and entrapped volume of the studied MLVs provided further evidence of the alteration of the liposomal bilayer as a consequence of the addition of beta-CD and/or the presence of the studied guests.

Layer by layer (LBL) assembly of poly(sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) was used to coat positively as well as negatively charged liposomes. The adsorption of either polyelectrolyte onto the liposomal surface occurs by means of electrostatic and hydrophobic interactions, depending on the structure of the polymer. The stability of the surface-modified liposomes was evaluated by monitoring the rate of the breakdown induced by the addition of increasing amounts of octaethyleneglycol mono-n-dodecylether (C12E8). Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) yielded insight into the morphology of the capsules before and after the impact with the surfactant.

A comparative thermodynamic investigation of the keto-enol interconversion reaction has been performed in several organic solvents and room-temperature ionic liquids (RTILs) to evaluate the role of the solvent and the effect of the ionic composition of RTILs. The tautomeric constant (KT) values at different temperatures have been analyzed in terms of the van't Hoff relationship to give the relevant thermodynamic parameters. The ΔG° values are the results of quite different combinations of the ΔH° and ΔS° values depending on the nature of the solvent. As expected, in conventional solvents, the tautomeric equilibrium is enthalpically disfavored and entropically favored by the increase in solvent polarity. In ionic liquids, the nature of the anion seems to play a primary role in the thermodynamics of the reaction that is endothermic and enthalpically driven in PF6- and TF2N-based RTILs and exothermic but entropically driven in BF4-based RTILs. The cation effect on the thermodynamics of the reaction is more complex and is consistent with a prevalence of the alkyl side chain segregation in the organization of the ILs.

Solute-solvent interactions on the keto-enol tautomerism of 2-nitrocyclohexanone in several organic solvents and room-temperature ionic liquids (RTILs) have been analyzed in terms of multiparameter equations. Permittivity and cohesive pressure values of the RTILs, unavailable by direct measurements, have been derived.

The presence of micelles from cationic and zwitterionic surfactants increases the apparent acidity of either the keto and the enol forms of 2-phenylacetylfuran ( 2PAF ) and 2-phenylacetylthiophene ( 2PAT ). This effect can be attributed to the affinity of the surfactant micelles for the enolate of the two substrates. Although the equilibrium constants for keto–enol tautomerism of 2PAF and 2PAT , K T =[enol]/[ketone]=p K a KH −p K a EH , do not change much, the presence of micelles provides an efficient method for producing appreciable quantities of the enolates under mild experimental conditions and in aqueous solutions. The obtained rate-profiles for the ketonisation reactions and the consistency of the kinetic rate constants over a wide range of ‘pH’ in several overlapping buffers indicate that the pH of the aqueous pseudophase (but not that at the micellar surface) can be controlled by buffers. Moreover, the increase of the acidity and the decrease of the ‘water’ rate of ketonisation of the enols of 2PAF and 2PAT upon addition of surfactants allow the uncovery of a metal ion catalysed pathway that cannot be observed in absence of surfactants.

Didodecyldimethylammonium bromide (DDAB) forms vesicles spontaneously by simple solubilization of the solid into water at a concentration of ≈2.5 mM. Vesicles can be observed by the increase in turbidity of the aqueous solution of DDAB and by the increase in absorbance (at λmax=490 nm) of a lipophilic dye (Sudan III) solubilized into the vesicular bilayer. This vesicle system has been perturbed by addition of single-chain surfactants in order to study the transition from a vesicle-stable region to a mixed-micelle region. Vesicle breakdown involves the initial incorporation of a single-chain surfactant into the vesicular bilayer, followed by subsequent disintegration of the vesicle. The progress of reaction has been observed by monitoring turbidity changes using a stopped-flow spectrophotometer. The rate of breakdown of vesicles depends on the concentration and hydrophobic properties of the added single-chain surfactant. In addition, hypertonic and hypotonic osmotic stresses have been investigated.

The ability of several organic compounds [alcohols 1 and 2, the corresponding phosphate esters 3 and 4 and their sodium salts 5 and 6 as well as some commercial surfactants such as C14DMAO (7, zwitterionic), SDS (8, anionic) and CTABr (9, cationic)] to produce supramolecular complexes with β-cyclodextrin has been investigated by four different techniques (ESI-MS, surface tension measurements, UV/Vis and 1H NMR spectroscopy). The data collected have allowed information about the formation of complexes and the location of the guest in the host to be gained. Comparison of the results obtained for phosphate esters and their salts, for both saturated and unsaturated derivatives, has made it possible to evaluate the factors that affect the stability of the supramolecular complexes under the different experimental conditions used. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).

The equilibrium constants for the keto-enol tautomerism of 2-phenacylfuran (2PF), KT = (enol)/(ketone), have been determined in water and in aqueous solutions of CTAB (cetyltrimethylammonium bromide) by combining the pKa KH for ionization of the ketone, directly measured in aqueous NaOH solutions, and the pKa EH for ionization of the enol, obtained from the corresponding rate profile of ketonization. Comparison of these equilibrium constants with those reported for some previously studied phenylacetyl- and phenacyl- heterocycles highlights the effect of an adjacent furyl group on keto-enol tautomerism. Moreover, it has been shown that micelles from cationic (CTAB) and zwitterionic (3-N,N-(dimethyl-N- myristylammonium)propanesulfonate) surfactants decrease the rate of ketonization of the enolate of 2PF and/or increase the apparent acidity of the keto form. These effects have been related to the affinity of the surfactant micelles for the enolate of 2PF. To the contrary, anionic surfactants (SDS: sodium dodecyl sulfate) do not display appreciable effects on the acidity of the keto form or on the kinetics of ketonization of the enol form of 2PF.

Kinetic data on the enolization reaction of 3-acetyl-5-methylisoxazole, 5-acetyl-3-methylisoxazole, 3(5)-acetylpyrazole and some previously studied acetylheterocycles have been the object of a comprehensive ab initio analysis. Enolization rate constants were measured spectrophotometrically by the halogen trapping technique at 25 °C and ionic strength of 0.3 mol dm−3 in water, in acetate buffers, in dilute hydrochloric acid, in dilute sodium hydroxide and in the presence of some metal ion salts. In the spontaneous (water) and base (acetate) catalysed reactions the ketones investigated are generally more reactive than acetophenone, according to the electron-withdrawing effect of the heterocyclic ring compared with the benzene ring. In particular, acetylisoxazoles, 3(5)-acetylpyrazole and acetylthiazoles are more reactive than acetylfurans, 2-acetylpyrrole and acetylthiophenes respectively, and this can be attributed to the additional effect of the second heteroatom in the heterocyclic moiety. On the other hand, the compounds investigated are generally less reactive than acetophenone in the H3O+-catalysed reaction. Ab initio calculations on the relative stability of the protonated and unprotonated forms of the substrates investigated have been compared with the kinetic results obtained in acid solutions. As far as the metal ion catalysis is concerned, an approach in terms of ΔΔE can give an estimate of the combined contributions of charge densities and frontier orbitals to the interaction of the substrate with the metal ion catalyst. A comparison of experimental metal activating factor values and ab initio calculations outlines the importance of charge density on the carbonyl oxygen atom of acetylheterocycles with one heteroatom. An analogous comparison for acetylheterocycles with two heteroatoms suggests the formation of a chelate complex or transition state, in which the metal ion coordinates both the carbonyl oxygen and the aza nitrogen, whenever these two atoms are suitably placed within the molecular structure of the acetylheterocycle. Copyright © 2002 John Wiley & Sons, Ltd.

We have developed a simple artificial photoresponsive ion-gating device by inserting molecular switches in the membrane of liposomes. A controlled and directed proton transport across the bilayer membrane can lower the internal pH of the liposomes from neutral to around 4 under combined light and chemical stimulation.

Rate constants for the enolisation reactions of title compounds have been measured by their rates of halogenation at 25 °C in water, in several buffers, in dilute hydrochloric acid, in dilute sodium hydroxide, and in the presence of some metal ion salts. The results have been compared with those previously obtained from the corresponding reactions of acetophenone and a number of other acetyl heterocycles. Electronegativity of the heteroatoms and the “π-excessive” nature of the heterocyclic rings appear to be the main factors determining the relative reactivities in the acid-catalysed reactions. Bronsted β values and isotope effects, kH/kD, point to a more symmetrical transition state for the investigated acetyl heterocycles than that for acetophenone in the general base-catalysed reaction. Metal-activating factors (MAF), i.e. the catalytic constant for metal-ion (Cu2+, Zn2+, and Ni2+) catalysis, kM, relative to that for proton catalysis, kH, are discussed as an empirical measure of the “hard or soft” character of the carbonyl groups in acyl heterocycles.

The keto–enol tautomerism of some cyclic 2-nitroalkanones was studied in cyclohexane. Keto–enol equilibrium constants, KT, at 25 °C were obtained from 1H NMR spectra. The relative enol content for the investigated ketones as a function of ring size decreases in the order 6 > 7 > 11 > 12 > 15. This trend apparently is different from that observed in water. Density functional theory (DFT) calculations have been performed to rationalize the effects of ring size and of the solvent on tautomerism. The acidity constants, KaKH, for the different keto tautomers were measured spectrophotometrically at 25 °C in buffered aqueous solutions. No simple correlations between KaKH and ring size was observed, and this is in agreement with a DFT analysis performed on the same compounds.

Inductive and mesomeric effects of the [60]fulleropyrrolidine (Pyr=C60) and the [60]fullerene (C60) molecular frameworks have been investigated by linear free energy relationship analyses. The electronic effects of these moieties have been studied by expressly designing [60]fulleropyrrolidine derivative 1, which has a C–H bond α to both a carbonyl group (C–Hα) and a C60 cage. The extent of polarization of such a bond was then used to probe electron-withdrawing perturbation induced by the fullerene sphere. Thermodynamic measurements based on both theoretical and experimental approaches allowed the acidity of ketone 1 to be measured; this resulted in about a 1 × 106-fold increase in acidity with respect to that of the structurally correlated acetophenone. Experimental and theoretical kinetic determinations were used to determine the stereolability of ketone 1, which was, in fact, chiral due to the stereogenic carbon α to the carbonyl group. Also, these results confirmed the very strong tendency for the C60 sphere to promote breaking of the C–Hα bond. Thismeans that the Pyr=C60 and C60 fragments are able to express electron-withdrawing effects stronger than those of halogen atoms, but less effective than those of carbonyl derivatives (e.g., ketones, carboxylic acids or acyl derivatives). Finally, the σp, σI and σR– descriptors of inductive and/or mesomeric effects were successfully estimated for both Pyr=C60 and C60 fragments thanks to the integrated use of an original procedure based on semi-empirical calculations and Hammett/Taft correlations involving mono- or dual-parameter equations.

A Zn–salophen complex has been incorporated into POPC large unilamellar liposomes (LUV) obtained in phosphate buffer at pH 7.4. Fluorescence optical microscopy and anisotropy measurements show that the complex is located at the liposomal surface, close to the polar headgroups. The interaction of the POPC phosphate group with Zn 2 + slowly leads to demetallation of the complex. The process follows first order kinetics and rate constants have been measured fluorimetrically in pure water and in buffered aqueous solution. The coordination of the phosphate group of monomeric POPC with salophen zinc also occurs in chloroform as detected by ESI-MS measurements. The effect of the Zn–salophen complex on the stability of POPC LUV has been evaluated at 25 °C by measuring the rate of release of entrapped 5(6)-carboxyfluorescein (CF) in the presence and in the absence of Triton X-100 as the perturbing agent. It turns out that the inclusion of the complex significantly increases the stability of POPC LUV.

The aggregation properties of a new sultaine surfactant have been studied in buffered aqueous solution at pH 7.4 under controlled condition of osmolarity. Spontaneously formed sultaine vesicles with a mean diameter of about 1 μm can be observed by optical microscopy. The phase behaviour of the surfactant has been investigated by differential scanning calorimetry (DSC) and Nile Red fluorescence. Two critical vesicular concentrations (CVC(1) and CVC(2)) have been fluorimetrically measured, by using pyrene and Nile Red as the fluorescent probes. The two populations of vesicles behave differently as a consequence of their size. The stability of extruded large unilamellar vesicles (LUV) formed slightly above the CVC(1) has been evaluated in the temperature range 25-75°C by following the rate of spontaneous release of entrapped 5(6)-carboxyfluorescein (CF). The stability of the same vesicles at 70°C has also been investigated under osmotic stress obtained by adding NaCl or sucrose to the bulk solution. At a sultaine concentration above the CVC(2) LUV tend to associate and form stable larger closely packed aggregates as suggested by Dynamic Laser Light Scattering and rheological measurements.

The equilibrium constants for ion pair formation of some pyridines have been evaluated by spectrophotometric titration with trifluoroacetic acid in different ionic liquids. The basicity order is the same in ionic liquids and in water. The substituent effect on the equilibrium constant has been discussed in terms of the Hammett equation. Pyridine basicity appears to be less sensitive to the substituent effect in ionic liquids than in water.

Second-order rate constants of the diethylamine-promoted enantiomerization of 2-[2-(1-methyl-1H-pyrrol-2-yl)-2-oxo-1-phenylethyl]-isoindole-1,3-dione, a chiral alpha-substituted ketone endowed with high anti-MAO activity type-A, were measured by dynamic high-performance liquid chromatography (DHPLC), stopped-flow high-performance liquid chromatography (sf-HPLC), and a classical method based on enantioselective HPLC as the monitoring tool. The chiral column used in all determinations was the commercial Chiralpak AD. By comparison of the obtained data, perturbing effects of the stationary phase on the DHPLC and sf-HPLC determinations were highlighted and distinguished in indirect (SP(IPC)) and direct (SP(DPC)) type. It was evidenced that SP(DPC) noise effects may be completely erased by simple mathematical treatment of data obtained at different concentrations of the basic catalyst. Perturbations of type SP(IPC) may instead only be partially kept down by modulating the concentration of the basic catalyst. An estimation of the density distribution of catalytic sites covalently bonded to the stationary phase (SP) of the Chiralpak AD was performed exploiting the quantified SP(DPC) effects. Such an approach might be of general application, supplying a useful way to characterize the attitude of SPs to speed acid- or base-catalyzed equilibria possibly active during chromatographic separations.

Stable homogeneous aqueous dispersions of pristine single-walled carbon nanotubes (SWNTs) are obtained by using a water-soluble long-chain imidazolium ionic liquid (hvimBr) above its critical micelle concentration. The amount of hivmBr and the sonication time are two essential factors to obtain a good dispersion. The effective concentration of exfoliated SWNTs in aqueous solution is determined by simple, convenient and rapid UV-visible spectrophotometric measurements.

While the solvent effect on the rate of tautomerization of 2-nitrocyclohexanone in several organic solvents appears to depend essentially on the permittivity of the solvent, a different behavior is observed in some ionic liquids. In particular the rate of the reaction in ionic liquids (ILs) is much faster than expected solely on the basis of the permittivity of the studied ILs. However, if more solvent parameters are taken into consideration (namely the polarizability, H-bond acidity, and cohesive pressure of the solvent) one comprehensive linear solvation energy relationship (LSER) for both organic and IL media can be obtained and no special "ionic liquid effect" can be highlighted. The kinetic results have also been discussed in terms of the Bronsted equation. It turns out that on passing from molecular solvents to ILs the transition state structure of the enolization reaction becomes markedly enolate-like (Bronsted beta value close to 1).