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This review is focussed on modelling the transport processes of different drugs across the intact human skin by introducing a memory formalism based on the fractional derivative approach. The fundamental assumption of the classic transport equation in the light of the Fick’s law is that the skin barrier behaves as a pseudo-homogeneous membrane and that its properties, summarized by the diffusion coefficient D, do not vary with time and position. This assumption does not hold in the case of a highly heterogeneous system as the skin is, whose outermost layer (the stratum corneum) is comprised of a multi-layered structure of keratinocytes embedded in a lamellar matrix of hydrophobic lipids, followed by the dermis that contains a network of capillaries that connect to the systemic circulation. A possible way to overcome these difficulties resides in the introduction of mathematical models which involve fractional derivatives to describe complex systems with interactions in space and time, following the model originally developed by Caputo in order to consider the memory effects in materials. Although the introduction of fractional derivatives to model memory effects is completely phenomenological, i.e., characterized by a single parameter, i.e., the fractional derivative order $$\nu ,$$ a number of authors have found that this approach can provide a better comparison to experimental data and that this technique may be alternative to integer-order derivative models. In this review, we aim to summarize some our recent results, concerning the transport of different diffusing compounds of different structural complexity across the intact skin.

The diffusion of drugs across a composite structure such as a biological membrane is a rather complex phenomenon, because of its inhomogeneous nature, yielding a diffusion rate and a drug solubility strongly dependent on the local position across the membrane itself. These problems are particularly strengthened in composite structures of a considerable thickness like, for example, the human skin, where the high heterogeneity provokes the transport through different simultaneous pathways. In this note, we propose a generalization of the diffusion model based on Fick’s 2nd equation by substituting a diffusion constant by means of the memory formalism approach (diffusion with memory). In particular, we employ two different definitions of the fractional derivative, i.e., the usual Caputo fractional derivative and a new definition recently proposed by Caputo and Fabrizio. The model predictions have been compared to experimental results concerning the permeation of two different compounds through human skin in vivo , such as piroxicam, an anti-inflammatory drug, and 4-cyanophenol, a test chemical model compound. Moreover, we have also considered water penetration across human stratum corneum and the diffusion of an antiviral agent employed as model drugs across the skin of male hairless rats. In all cases, a satisfactory good agreement based on the diffusion with memory has been found. However, the model based on the new definition of fractional derivative gives a better description of the experimental data, on the basis of the residuals analysis. The use of the new definition widens the applicability of the fractional derivative to diffusion processes in highly heterogeneous systems.

Nanostructured polymers, with different morphologies and different spatial organizations, have found, in last few years, a wide range of uses in humidity sensors, as a viable alternative to ceramic or semiconducting materials and to oxides (perovskite) compounds. Their enhanced sensitivity towards external stimuli has made them ideal candidates in the design of humidity sensors. This is mainly due to the fact that nanostructured polymers, when embedded with different content of water, represent a heterogeneous system whose dielectric and conductometric properties varies over a wide range, resulting in advantageous sensitive material in resistive-type or capacitive-type humidity sensors. The most notable property of nanostructured polymers is their inherent electrical behavior which is closely connected to the presence of heterogeneities at a nano- or micro-scale level. In the first part of this paper, we discuss and justify, on the basis of the dielectric theory of heterogeneous systems, how the dielectric properties of nanostructured polymers, independently of their chemical nature, could vary as a consequence of a different amount of water adsorption, meeting the basic requirement of any humidity sensor device. In particular, we have analyzed systems with different porosity and different pore interconnections to cover the most part of the structural arrangements and morphologies nanostructured polymers give rise. In the second part of the paper, we present some remarkable examples of nanostructured polymers employed in the fabrication of humidity sensors based on changes in the electrical properties (permittivity and electrical conductivity) upon exposure to moisture, highlighting the main features that make them suitable for sensors, with specific emphasis to characteristic parameters, such as sensitivity, response time, hysteresis and durability.

In this note, we present a simple mathematical model of drug delivery through transdermal patches by introducing a memory formalism in the classical Fick diffusion equation based on the fractional derivative. This approach is developed in the case of a medicated adhesive patch placed on the skin to deliver a time released dose of medication through the skin towards the bloodstream.The main resistance to drug transport across the skin resides in the diffusion through its outermost layer (the stratum corneum). Due to the complicated architecture of this region, a model based on a constant diffusivity in a steady-state condition results in too simplistic assumptions and more refined models are required.The introduction of a memory formalism in the diffusion process, where diffusion parameters depend at a certain time or position on what happens at preceeding times, meets this requirement and allows a significantly better description of the experimental results.The present model may be useful not only for analyzing the rate of skin permeation but also for predicting the drug concentration after transdermal drug delivery depending on the diffusion characteristics of the patch (its thickness and pseudo-diffusion coefficient).

Dielectric models of biological cells are generally based on spherical or ellipsoidal geometries, where the different adjoining dielectric media are arranged as distinct core and shells, representing the cytosol and the cell membrane. For ellipsoidal particles, this approach implies the assumption of confocal shells that, in turn, means a cell membrane of ill-defined thickness. A quantitative analysis of the influence of a non-uniform thickness of the cell membrane has been not considered so far. In the case of a toroidal particle, this problem can be conveniently addressed by considering the solution of the Laplace equation in two different coordinate systems, i.e., toroidal coordinates ( confocal shells and hence non-uniform thickness of the shell membrane) and toroidal polar coordinate, ( concentric shells and hence a uniform thickness of the shell membrane). In the present paper, we compare the dielectric spectra of a toroidal particle aqueous suspension obtained from the two above stated solutions of the Laplace equation and we furnish a first quantitative estimate of the differences arising from considering the presence of confocal or concentric shells. This approach offers a complete view of the influence of the membrane thickness on the whole dielectric spectrum of a biological particle suspension, at least as far as toroidal objects are concerned.

This article reviews the most recent literature data on the applications of gold nanoparticles and their various conjugates which make them suitable structures towards biomedical and clinical purposes, with an emphasis on their use as drug delivery vehicles for selective targeting of cancer cells. With the rapid surge in the development of nanomaterials, new methodologies and treatment strategies have been explored and these topics should be taken into consideration when a current scenario is required in the design of new experimental approaches or in a comprehensive data interpretation. We present here a summary of the main properties of gold nanoparticles and their conjugates and the state-of-the-art of non-conventional treatment in targeted drug delivery based on gold nanoparticles as carriers, with the aim to give the reader an overview of the most significant advances in this field. This journal is © the Partner Organisations 2014.

A recently patented one-step methodology was used for the formulation of chitosan (CS) coated polylactic-co-glycolic acid (PLGA) nanoparticles containing dexamethasone (DXM) as a model drug. SEM investigations showed that nanoparticles (NPs) were spherical in shape with smooth surface. CS coating switched NPs ζ-potential from negative to positive, without modifying particle size distribution. Moreover, CS coating allowed a significant modulation of in vitro drug release, providing a sustained drug delivery in cultured cells. The uptake of fluorescent CS-coated PLGA NPs by hepatocytes (C3A) and fibroblasts (3T6) as well as the fate of internalized NPs were investigated by confocal microscopy. 3T6 and C3A cells were treated with DXM-loaded NPs and experiments were addressed to analyze the specific cell response to DXM, in order to evaluate its functional efficiency in comparison with conventional addition to culture medium. CS-coating of DXM loaded PLGA NPs allowed their uptake by cultured cells without inducing cytotoxicity.

Water close to proteins plays a key role in determining their structural and functional properties. Despite being a subject of considerable interest, the characterization of hydration water, as far as its total amount is concerned, is still controversial and its influence on protein structure and folding is not yet fully understood. In this work, we have investigated the dielectric properties of lysozyme aqueous solutions over the frequency range where the orientational polarization relaxation of the aqueous phase occurs (from 500 MHz to 50 GHz). Measurements extend over a wide concentration range, up to 300 mg/mL, corresponding to a volume fraction of the order of 0.4. The analysis of the dielectric spectra, based on the decrease of the dielectric increment of the γ-dispersion as a function of protein concentration, allows us to estimate the total amount of hydration water (both bound water and loosely bound water) present in the system investigated. We observe a decrease of the hydration number as a function of the protein concentration. This behavior is well accounted for by considering the formation of small equilibrium clusters with aggregation number of some units, as recently reported by Stradner et al. (1) on the basis of small-angle X-ray and neutron scattering measurements.

The influence of localized charge distributions at the interfaces of spherical colloidal particles in aqueous suspension is discussed in the light of the effective medium approximation theory of heterogeneous systems. The approach is shown to give analytical results in the case of shelled particles with the presence of two distinct interfaces. The whole dielectric response of the system gives rise to different relaxation contributions, falling in different frequency regions and attributed to different polarization mechanisms, at a molecular level. In particular, the number and the strength of the dielectric relaxations associated with the presence of localized charges is discussed.

The radiowave dielectric properties of aqueous solutions of thermosensitive copolymers, consisting of poly(2-acrylamido-2-methylpropanesulfonate) [PAMPS] and poly(N-isopropylacrylamide) [PNIPAAM] with different block lengths, have been investigated over a broad temperature and frequency range. These copolymers PAMPS(n)-b-PNIPAAM(m) form temperature responsive aggregates (micelles) that represent a class of self-assembled structures in water of great interest because of their potential use as drug delivery formulations and in diverse biotechnological applications. Copolymers formed by hydrophilic segments covalently attached to a hydrophobic segments are capable of forming a micellar structure as soon as the temperature is raised above their lower critical solution temperature. We have investigated the dielectric properties of PAMPS(n)-b-PNIPAAM(m) diblock copolymers with different lengths of the hydrophilic and hydrophobic segments during the whole aggregation process driven by the progressive increase of temperature. The process has been followed by the changes resulting in the dielectric parameters (the dielectric increment Δε and the relaxation frequency ν(0)) of the whole aqueous solution. The dielectric response of the micelles has been described within the framework of the standard electrokinetic model for charged colloidal particles, and the main characteristic parameters have been evaluated. Subsequent cross-linking of these diblock copolymers by a cationic PEO(x)-b-PAMPTMA(y) polyelectrolyte yields hybrid core-shell-corona systems, with the PNIPAAM hydrophobic blocks collapsed in the core, an interpolyelectrolyte chain complex forming the shell, and the hydrophilic PEO chains as an external corona. In this case too, the dielectric spectra can be appropriately accounted for within the same theoretical framework.

A modified emulsion copolymerization of phenylacetylene (PA) with hydrophilic monomers having different functions, i.e., acrylic acid (AA) and N,N-dimethylpropargylamine (DMPA) respectively, yields functionalized polymeric P(PA-co-AA) and P(PA-co-DMPA) nanoparticles. The systematic investigation on the experimental parameters affecting size, surface charge and polydispersity of the copolymers (initiator concentration, reaction time, cosolvent and PA/comonomer ratios) allows to modulate the nanoparticle physico-chemical properties. Spherical shaped particles with diameters in the range 80-500 nm, low polydispersity (PI values in the range 1.11-1.30) and different surface charge densities, between 0.44 and 2.87 microC/cm(2), have been consistently obtained and characterized by means of Dynamic Light Scattering (DLS), laser Doppler electrophoretic and Scanning Electron Microscopy (SEM) studies. XPS measurements have provided information on the nanoparticles chemical surface structure and suggest that AA and DMPA units are preferentially distributed on the surface of the spheres. The nanospheres self-assemble giving large domains (9.5 x 14.5 microm). Photonic analysis of the self-assembled copolymeric nanoparticles has been performed by means of Spectroscopic Ellipsometry (SE) and Bragg reflection spectroscopy, both of them demonstrating a three-dimensional photonic crystal property of these systems.

The influence of the cell shape on the dielectric and conductometric properties of biological cell suspensions has been investigated from a theoretical point of view presenting an analytical solution of the electrostatic problem in the case of prolate and oblate spheroidal geometries. The model, which extends to spheroidal geometries the approach developed by other researchers in the case of a spherical geometry, takes explicitly into account the charge distributions at the cell membrane interfaces. The presence of these charge distributions, which govern the trans-membrane potential DeltaV, produces composite dielectric spectra with two contiguous relaxation processes, known as the alpha-dispersion and the beta-dispersion. By using this approach, we present a series of dielectric spectra for different values of the different electrical parameters (the permittivity epsilon and the electrical conductivity sigma, together with the surface conductivity gamma due to the surface charge distribution) that define the whole behavior of the system. In particular, we analyze the interplay between the parameters governing the alpha-dispersion and those influencing the beta-dispersion. Even if these relaxation processes generally occur in well-separated frequency ranges, it is worth noting that, for certain values of the membrane conductivity, the high-frequency dispersion attributed to the Maxwell-Wagner effect is influenced not only by the bulk electrical parameters of the different adjacent media, but also by the surface conductivity at the two membrane interfaces.

The alterations of the passive electrical parameters (the permittivity epsilon and the electrical conductivity sigma) of human erythrocyte cell membrane induced by the presence of glucose in the extracellular medium have been investigated by means of dielectric spectroscopy measurements. The membrane permittivity epsilon(s) and the permittivity epsilon(p) and electrical conductivity sigma(p) of the cytosol have been evaluated on the basis of a recent analytical model proposed by Prodan et al., 1983 [16], that takes into account the whole dielectric spectrum of a cell suspension, consisting of both the low-frequency alpha-dispersion and the high-frequency beta-dispersion. Our results show a marked increase of the membrane permittivity epsilon(s) close to a glucose concentration of 20mM. On the contrary, the electrical properties of the cytosol do not change appreciably. This finding strengthens the hypothesis that glucose interactions involve primarily the cell membrane and the mechanism of the transport is briefly discussed.

We investigated the dielectric properties of aqueous solutions of a grafted copolymer, consisting of a polysaccharide, Dextran, grafted with a thermo-sensitive polymer, poly(N-isopropylacrylamide), [pNIPAAM], over broad temperature and frequency ranges. The graft copolymers, prepared by atom-transfer radical polymerization [ATRP], form temperature-responsive materials that represent a class of self-assembled structures in water of great interest because of their potential use as drug delivery formulations and in diverse biotechnological applications. In these systems, in the dilute regime and below the lower critical solution temperature, relaxation modes corresponding to two different length-scales have been observed and analyzed in terms of ion fluctuation dielectric models specifically developed to describe the dielectric relaxation in highly charged polyion aqueous solutions. Regardless of whether the ions were produced by the ionization of the polymer chain, as in polyelectrolyte solutions, or not, as in the present case, they represent a probe at a microscopic level that is expected to reveal the structural characteristics of the system at different scales. We have identified a characteristic length associated with the size of the polymer coil in the dilute regime and a length due to fixed cross-links, where ions are partially localized by the local profile of the Coulombic field. These lengths are in reasonable agreement with analogous lengths derived from structural information and from the hydrodynamic radius of the polymer coils, measured by means of a dynamic light-scattering technique.

Interaction of charged particles, induced by adding an oppositely charged polyion, gives rise to intriguing aggregation phenomena. The presence of short-range interactions in competition with electrostatic repulsions results, in an interval of concentrations around the inversion point, in the formations of long-lived clusters of polyelectrolyte-decorated particles. We will show that the whole aggregation scenario can be justified as due to an heterogeneous charge distribution at the particle surface, as a consequence of the correlated polyion adsorption, on the basis of a recently model proposed by D. Velegol, P. Thwar, Langmuir 17 (2001) 7687–7693.

Polymer chains adsorbed onto oppositely charged spherical colloidal particles can significantly modify the particle-particle interactions. For sufficient amounts of added polymers, the original electrostatic repulsion can even turn into an effective attraction and relatively large kinetically stable aggregates can form which display several unexpected and interesting peculiarities and some intriguing biotechnological implications. The attractive interaction contribution between two oppositely particles arises from the correlated adsorption of polyions at the oppositely charged particle surfaces, resulting in a non-homogeneous surface charge distribution. Here, we investigate the aggregation kinetics of polyion-induced colloidal complexes through Monte Carlo simulation, in which the effect of charge anisotropy is taken into account by a DLVO-like intra-particle potential, as recentely proposed by Velegol and Thwar [D. Velegol and P.K. Thwar, Langmuir, 17, 2001]. The results reveal that in the presence of a charge heterogeneity the aggregation process slows down due to the progressive increase of the potential barrier height upon clustering. Within this framework, the experimentally observed cluster phases in polyelectrolyte-liposomes solutions should be considered as a kinetic arrested state., Comment: 9 pages. 11 figures

Lipid-DNA complexes (lipoplexes) are widely used, since several years, as gene carriers. However, their transfection efficiency, both in vitro and in vivo, depends, in a rather complex way, on different interconnected parameters, ranging from the chemical composition of the lipid components to the size and size distribution of the complexes and, moreover, to the composition of the suspending medium. In this paper, we have investigated the behavior of nine different commercially available transfection agents (liposomal and non-liposomal) and their lipoplexes, at different molar charge ratios and in different experimental conditions. The size and the time stability of the resulting lipoplexes were investigated by means of dynamic light scattering methods and their toxicity and transfection efficiency were assayed in vitro in a model tumor cell line (C6 rat glioma cell line). An attempt to correlate the different parameters governing the complex phenomenology observed has been made. Whereas all the formulations investigated display a low toxicity, that increases with the increase of the lipid-DNA molar charge ratio, the transfection efficiency markedly depends, besides the molar charge ratio, on the lipid composition and on the lipoplex size, in a rather correlated way. The aim of this work is to present, in a wide scenario, an example of the inter-correlation among the different parameters that influence the transfection efficiency of lipoplexes and to suggest the role exerted by the average size of the resulting aggregates in their overall effectiveness as carriers in gene therapy.

We have investigated the formation of complexes between negatively charged niosomal vesicles (hybrid niosomes), built up by dicethylphosphate [DCP], Tween 20 and Cholesterol, and three linear differently charged cationic polyions, such as alpha-polylysine, epsilon-polylysine, and polyethylvinylpyridinium bromide [PEVP], with two different substitution degrees. Our aim is to investigate the interaction mechanism between anionic-nonionic vesicles (hybrid niosomes) and linear polycations, characterizing the resulting aggregates in view of possible applications of these composite colloidal particles as vectors for multidrug delivery. In order to explore the aggregation behavior of the complexes and to gain information on the stability of the single niosomal vesicles within the aggregates, we employed dynamic light scattering (DLS), laser Doppler electrophoretic measurements, and fluorescence measurement techniques. The overall phenomenology is well described in terms of the re-entrant condensation and charge inversion behavior, observed in different colloidal systems. The aggregate size and overall charge depend on the charge ratio between vesicles and polyions, and the aggregates reach their maximum size at the point of charge inversion (re-entrant condensation). While the overall phenomenology is similar for all three polycations investigated, the stability and the integrity of the hybrid niosomal vesicles forming the aggregates strongly depend on the chemical structure of the polycations. The role of the polycations in the aggregation process is discussed by identifying specific interactions with the niosomal membrane, pointing out their importance for possible applications as drug delivery vectors.

The thermodynamic behavior of mixed DOTAP-DPPC monolayers at the air--water interface has been investigated in the temperature range from 15 to 45 degrees C, covering the temperature interval where the thermotropic phase transition of DPPC, from solid-like to liquid-like, takes place. Based on the regular solution theory, the miscibility of the two lipids in the mixed monolayer was evaluated in terms of the excess Gibbs free energy of mixing Delta G(ex), activity coefficients f(1) and f(2) and interaction parameter omega between the two lipids. The mixed DOTAP-DPPC film was found to have positive deviations from ideality at low DOTAP mole fractions, indicating a phase-separated binary mixture. This effect depends on the temperature and is largely conditioned by the structural chain conformation of the DPPC lipid monolayer. The thermodynamic parameters associated to the stability and the miscibility of these two lipids in a monolayer structure have been discussed in the light of the phase diagram of the DOTAP-DPPC aqueous mixtures obtained from differential scanning calorimetry measurements. The correlation between the temperature behavior of DOTAP-DPPC monolayers and their bulk aqueous mixtures has been briefly discussed. (c) 2007 Elsevier B.V. All rights reserved.

The dielectric spectra of aqueous suspensions of unilamellar liposomial vesicles built up by zwitterionic phospholipids (dipalmitoylphosphatidyl-choline, DPPC) were measured over the frequency range extending from 1 kHz to 10 MHz, where the interfacial polarization effects, due to the highly heterogeneous properties of the system, prevail. The dielectric parameters, i.e., the permittivity epsilon '(omega) and the electrical conductivity sigma(omega), have been analyzed in terms of dielectric models based on the effective medium approximation theory, considering the contribution associated with the bulk ion diffusion on both sides of the aqueous interfaces. The zwitterionic character of the lipidic bilayer has been modeled by introducing an 'apparent' surface charge density at both the inner and outer aqueous interface, which causes a tangential ion diffusion similar to the one occurring in charged colloidal particle suspensions. A good agreement with the experimental results has been found for all the liposomes investigated, with size ranging from 100 to 1000 nm in diameter, and the most relevant parameters have briefly discussed in the light of the effective medium approximation theory. (C) 2006 Elsevier B.V. All rights reserved.

With the growing interest in the applications of gold nanoparticles in biotechnology and their physiological effects, possible toxicity of gold nanoparticles is becoming an increasingly important issue. A large number of studies carried out over the past few years under a variety of experimental conditions and following different protocols have produced conflicting results, leading to divergent views about the actual safety of gold nanoparticles in human applications. This work is intended to provide an overview of the most recent experimental results and thereby summarize current state-of-the-art. Rather than presenting a comprehensive review of the available literature in this field, which would be impractically broad, we have selected representative examples of both in vivo and in vitro studies, which clearly demonstrate the need for urgent and rigorous standardization of experimental protocols. Despite their significant potential, the safety of gold nanoparticles is highly controversial at this time, and important concerns have been raised that need to be properly addressed. Factors such as shape, size, surface charge, coating, and surface functionalization are expected to influence the interactions of particles with biological systems to a different extent, resulting in different outcomes and influencing the potential of gold nanoparticles for biomedical applications. Moreover, despite continuous attempts to establish a correlation between structure of the particles and their interactions with biological systems, we are still far from elucidating the toxicological profile of gold nanoparticles in an indisputable manner. This review is intended to contribute towards this goal, offering a number of suggestions on how to achieve the systematization of data on the most relevant physico-chemical parameters, which govern and control the toxicity of gold nanoparticles at cellular and whole-organism levels. [Figure not available: see fulltext.]

This review focuses on some recent advances made in the field of gas sensors based on polyaniline [PANI], a conducting polymer with excellent electronic conductivity and electrochemical properties. Conducting polymers represent an important class of organic materials with an enhanced resistivity towards external stimuli. Among them, PANI polymers have attracted wide interest because of the versatility in their use, combined with the easy of synthesis, high yield and good environmental stability, together with a favorable response to guest molecules at room temperature. Moreover, PANI can be shaped into various structures with different morphologies and the possibility of obtaining nanofibers, in addition to thin films, has opened a rapid development of ultrasensitive chemical sensors, with improved processability and functionality. This review provides a brief description of the current status of gas chemiresistive sensors based on polyaniline and highlights the properties and applications of these devices in diverse range of applications.

Because of the growing interest of gold nanoparticles in biomedical and biotechnological applications, their toxicity is becoming an increasingly important issue and, in the last few years, there has been continuously expanding research activity in this field. However, due to the intrinsic complexity of the problem, together with the lack in the standardization of the experimental procedures, there is to date a large scattering of the results that still prevents reaching a general consensus of the possible toxic effects of gold nanoparticles in biological systems of increasing complexity (cell membrane, cells, tissues, organs and human body). The strong need to systematize the data suggests employing an appropriate metric, as far as the particle concentration is concerned, that could help in comparing and organizing the available data in a more intelligible scenario. In this note, some recent literature data on the viability of HeLa cells exposed to differently functionalized gold nanoparticles have been analyzed on the basis of a metric based on the numerical particle concentration (number of particles per unit volume of cell culture) that, to a certain extent, takes into account both the size and the shape of nanoparticles. This analysis offers a much more intelligible behavior than the one based on metrics that considers mass concentration (molar concentration) or particle size. At least, in the particular case of HeLa cells, the analysis of the data shows that differently functionalized gold nanoparticles behave similarly and that the different surface coating of the different nanoparticles considered defines the range of particle concentration where toxic effects begin. This kind of analysis could furnish some albeit preliminary suggestions towards an appropriate method to study gold nanoparticle toxicity.

Core-shell gold nanoparticles [AuNPs], stabilized with a hydrophilic polymer, poly(3-dimethylammonium-1-propyne hydrochloride) [PDMPAHCl], have been used for the immobilization of bovine serum amine oxidase [BSAO]. The functionalized surface of the hybrid nanoparticles is pH responsive, due to the presence of aminic groups that carry out a double role: on one hand they act as ligands for the gold nanoparticle surface, allowing the colloidal stabilization and, on the other hand, they give a hydrophilic characteristic to the whole colloidal suspension. The core-shell nanoparticles [Au@PDMPAHCl] have been characterized by using UV-vis and X-ray photoelectron spectroscopy, DLS, ζ-potential measurements and by FE-TEM microscopy. BSAO enzyme can be loaded by non-covalent immobilization onto Au@PDMPAHCl nanoparticles up to 70% in weight, depending on the pH values of the environmental medium. Activity tests on Au@PDMPAHCl-BSAO bioconjugates confirm an enzymatic activity up to 40%, with respect to the free enzyme activity. Moreover, our results show that loading and enzymatic activity are rather interrelated characteristics and that, under appropriate polymer concentration and pH conditions, a satisfactory compromise can be reached. These results, as a whole, indicate that Au@PDMPAHCl-BSAO bioconjugate systems are promising for future biomedical applications.

In this paper we report a comparative characterization of Small Unilamellar Vesicles (SUVs), Large Unilamellar Vesicles (LUVs) and Multilamellar Vesicles (MLVs) prepared from 1-palmitoyl-2-oleoyl- sn -glycero-3-phospatidylcholine (POPC), carried out using two NMR techniques, namely High Resolution NMR in solution and High Resolution–Magic Angle Spinning (HR-MAS). The size and size distributions of these vesicles were investigated using the dynamic light scattering technique. An improved assignment of the 1 H-NMR spectrum of MLVs is also reported. Keywords: Liposomes, unilamellar vesicles, multilamellar vesicles, NMR, HR-MAS, dynamic light scattering. Introduction Liposomes, or vesicles, are self-closed spherical or ellipsoidal structures where one or more phospholipid bilayers entrap part of the solvent into their interior [1, 2]. They are widely [3] studied not only as a model for cell membranes and transport phenomena across membranes but also for their great potential in applications such as drug delivery vehicles [4, 5]. Liposomes can be distinguished on the basis of both their physical characteristics and the method of preparation [6]. According to the size

We have investigated the complexation process between cationic liposomes built up by dioleoyltrimethylammoniumpropane [DOTAP] and linear polyelectrolytes, employing three different polyions with different charge density and flexibility, such as a single-stranded (ss)DNA, a double-stranded (ds)DNA and the sodium polyacrylate [NaPAA]. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements support a “reentrant condensation” scenario and suggest the presence of an arrested state occurring in polyelectrolyte–liposome suspensions, in the presence of high salt concentration. A simple phenomenological model is presented, describing the formation of large “equilibrium clusters”, close to the isoelectric condition.

The interaction of the three main components of the mitochondrial membrane, namely cardiolipin, phosphatidylcholine, and phosphatidylethanolamine, has been studied investigating mixed cardiolipin-phosphatidylcholine and cardiolipin-phosphatidylethanolamine monolayers at different cardiolipin molar fractions. The thermodynamic behavior of the mixed monolayers was investigated by means of surface pressure and surface potential measurements, and atomic force microscopy was employed to characterize the morphology of the monolayers. Langmuir isotherms and surface potential curves show a regular behavior with a progressive transition toward the isotherm of the pure component. Positive deviations from ideality in the excess Gibbs energies of mixing suggest the presence of repulsive interactions in both systems. Analysis of partial molecular dipole moment indicates a discontinuity at a definite cardiolipin/phosphatidylethanolamine molar fraction, suggesting the formation of a stoichiometric complex; as a consequence, in mixed cardiolipin-phosphatidylethanolamine monolayers, a phase separation is observed at phosphatidylethanolamine excess. AFM measurements indicate the presence of two domains: one made by phosphatidylethanolamine and the other by a regular arrangement of phosphatidylethanolamine and cardiolipin at a fixed molecular ratio.

Although complexation of charged particles induced by polyions of opposite charge is a well-known phenomenon, the possibility of obtaining equilibrium clusters stuck together by flexible polyions, which act as an electrostatic glue, is not completely recognized. In this Letter, we call attention towards the behavior of polyions in attaching together charged particles, by means of controlled electrostatic interactions. As an example, we present some features of equilibrium clusters composed of cationic liposomes built up by DOTAP and glued up by an anionic polyion, polyacrylate sodium salt. We discuss briefly some applications in nanostructure science and biotechnology.

The possible influence of the cell shape on the derivation of the passive electrical parameters of a biological cell membrane is discussed in light of two different models which describe the cell as a shelled ellipsoidal particle and as a biconcave disk obtained by the revolution of the Cassini oval, respectively. Whereas within the first model, the Laplace equation can be solved analytically, in the second one a numerical algorithm based on the boundary element method has been employed. We have compared the results obtained by these two different models in the case of normal human erythrocyte cell membrane, using radiowave dielectric spectroscopy measurements. Our findings show that, although in principle the cell shape might deeply affect the evaluation of the passive electrical parameters of the cell membrane, in the case of the erythrocyte shape modelled by the Cassini curve, only small deviations are evidenced in comparison to the values derived, as usually done in the dielectric spectroscopy of biological cell suspensions, from an ellipsoidal model analysis. This result gives further support to the reliability of the data reported in the literature based on an ellipsoidal shape erythrocyte model.

Three different techniques--light scattering, radiowave dielectric spectroscopy, and fluorescence were employed to investigate conformational variations in Escherichia coli ribosomes induced by removal of specific proteins. To this end, particles were treated with lithium chloride at different ion strength values to produce ribosomal cores. It was previously observed that treatment of ribosomes to subdenaturing temperatures promotes a structural rearrangement that implies a higher exposure of ribosomal RNA to the solvent. Results presented here strongly suggest that protein elimination from the ribosomal particle produces an overall response recalling the same variation of physical parameters previously observed after thermal treatment. We therefore suggest that high salt treatment produces the same structural modification caused by exposure to subdenaturing temperatures.

The dielectric and conductometric properties of aqueous polyelectrolyte solutions present a very complex phenomenology, not yet completely understood, differing from the properties of both neutral macromolecular solutions and of simple electrolytes. Three relaxations are evident in dielectric spectroscopy of aqueous polyelectrolyte solutions. Near 17 GHz, water molecules relax and hence this highest frequency relaxation gives information on the state of water in the solution. At lower frequencies in the MHz range, free counterions respond to the applied field and polarize on the scale of the correlation length. This intermediate frequency relaxation thus provides information about the effective charge on the polyelectrolyte chains, and the fraction of condensed counterions. However, the presence of polar side chains adds a further polarization mechanism that also contributes in this intermediate frequency range. At still lower frequencies, the condensed counterions polarize in a non-uniform way along the polyelectrolyte chain backbone and dielectric spectroscopy in the kHz range may determine the effective friction coefficient of condensed counterions. In this review, we analyse in detail the dielectric and conductometric behaviour of aqueous polyelectrolyte solutions in the light of recent scaling theories for polyelectrolyte conformation and summarize the state-of-the-art in this field.

Soluble conjugated polymers were obtained in the presence of Pd(II), Pt(II) and Rh(I) complexes from monosubstituted acetylene 3-dimethylamino-1-propyne (HC≡CCH2N(CH3)2, 1) and the corresponding hydrochloride (HC≡CCH2N(CH3)2·HCl, 2) and hydrobromide (HC≡CCH2N(CH3)2·HBr, 3) derivatives. A series of reactions were performed to achieve the optimization of the polymerization conditions. The highest yields were found for polymers synthesized using Pd(II) bisacetylides specially prepared, i.e. trans-[Pd(PPh3)2(C≡CCH2N(CH3)2)2], trans-[Pd(PPh3)2(C≡CCH2N(CH3)2)2HCl] and trans-[Pd(PPh3)2(C≡CCH2N(CH3)2)2HBr], respectively. The dimension and size distribution of the polymers were investigated using dynamic light scattering. Polymers containing quaternary ammonium groups showed evidence of a hydrodynamic radius of about 300 nm if prepared with the Rh(I) catalyst and of 160 nm if prepared with the Pd(II) catalysts. Polymers obtained from 1 showed smaller hydrodynamic radius compared to polymers obtained from 2 and 3, regardless the polymerization catalyst. The ionic polymeric materials were soluble in organic solvents and, more interestingly, in water. The formation of nanoparticles with pearl-like morphology was achieved using a recently developed osmosis-based method, with dimensions varying from 60 nm up to micrometres. Copyright © 2011 Society of Chemical Industry

The thermodynamic behaviour of mixed cationic–zwitterionic lipid mixtures dioleoyltrimethylammoniumpropane–dipalmitoylphosphatidylcholine (DOTAP–DPPC) at different mole fractions have been investigated by means of surface pressure measurements (Langmuir isotherms). Excess Gibbs energies of mixing have been calculated as a function of layer composition and surface pressure. Deviation from ideality evidences different molecular organisation of the two lipids, yielding the formation of cationic lipid domains in a zwitterionic lipid matrix. The stability of the mixed monolayer in the presence of both a simple electrolyte solution (NaCl) and a polyelectrolyte solution (NaPAA of different molecular weights) in the same charge ratio interval has been investigated and the influence of the polymer conformation briefly discussed.

The synthesis of a series of cationic lipids for the preparation of liposomes to be used in gene therapy is described. The synthetic strategy is designed in few steps and affords good yields. To cite this article: A. Bianco et al., C. R. Chimie 6 (2003).

An approach to electrical impedance tomography (EIT) data acquisition inspired by NMR-filtered back-projection imaging with fan isochromat distribution is proposed. A current projection is generated by injecting current at a certain point of the sample and simultaneously collecting the current itself at different points on the half space opposite the point of current injection. After that, the injection is shifted to another point and collected as above and so on. A very simple algebra and software support the numerical simulations. This method is expected to be more sensitive than the traditional method based on potential measurements. A preliminary low resolution experiment is presented.

Using the dielectric strength and relaxation time of a high-frequency (1 MHz−1 GHz) dielectric relaxation, we estimate the effective charge on polyelectrolytes and their net thermodynamic repulsive...

The radiowave dielectric behavior of sodium polyacrylate (NaPAA) aqueous solutions, in an extended concentration range and at various degrees of polymerization, was analyzed in the light of the scaling approach for polyelectrolyte solutions recently proposed by Dobrynin et al. [Macromolecules 1995, 28, 1859]. In the frequency range from 1 MHz to 1 GHz, the observed dielectric relaxation is attributed to the fluctuation of loosely bound counterions over a characteristic correlation length which depends on the polymer concentration. Assuming that free counterions fluctuate on a length scale that is proportional to the correlation length ξ0 of the semidilute solution, we derived power laws for the dielectric strength Δe and the relaxation frequency ν0. In agreement with our recently published data on conductivity, the dielectric data indicate that the effective charge on the NaPAA chains increases as concentration is raised, until the correlation length reaches the size of the electrostatic blob. By comparin...

Two different dielectric models of biological cell suspensions have been used to describe the dielectric and conductive properties of the membrane of erythrocyte cells. The passive electrical properties of the cell membrane (the membrane permittivity e ′ and the membrane conductivity σ ) have been evaluated on the basis of the Maxwell–Wagner–Hanai and Looyenga mixture equations and the results have been compared in order to discuss the validity of the two models employed. Based on a simultaneous fit of the permittivity e ′ and the electrical conductivity σ , the Looyenga equation furnishes a better description of the dielectric behavior of an erythrocyte cell suspension over an extended frequency range, in comparison to the Maxwell–Wagner–Hanai equation.

The d.c. electrical conductivity of polyacrylate sodium salt and poly(acrylic acid) aqueous solutions of different molecular weights from 2 to 200 kD has been investigated in a wide range of polymer concentration, covering both the semidilute (unentangled and entangled) and concentrated regimes. The data have been analyzed on the basis of a modified version of the Manning theory of counterion condensation, to cover the semidilute regime, taking into account scaling arguments recently proposed by Dobrynin et al. (Macromolecules 1995, 28, 1859). This analysis, on the basis of the conductivity model we have adopted, provides evidence for a fraction of free counterions that increases with the polymer concentration until the semidilute-concentrated crossover concentration is reached, suggesting that, in the concentration range investigated, the effective charge on the polyion is dependent on the polymer concentration. Moreover, at the higher concentrations investigated, our data suggest that a regime is attain...

Hyaluronic acid (HA) and alginate (AL) covalent nanogels cross-linked with l-lysine ethyl ester were prepared by template chemical cross-linking of the polysaccharide in polyion complex micelle (PIC) nanoreactors. By using this method we were able to prepare HA and AL nanogels without organic solvents. PICs were prepared by using poly(ethylene oxide)-block-poly[(3-acrylamidopropyl)- trimethylammonium chloride] (PEO-b-PAMPTMA) or poly[(N-isopropylacrylamide)- block-PAMPTMA] (PNIPAAM-b-PAMPTMA). Only PNIPAAM-b-PAMPTMA block copolymers allowed to prepare PIC with small and controlled size. Short polysaccharide chains (Xn = 50 and 63 for AL and HA, respectively, where X n is the number of monosaccharidic units present in the polysaccharide) where used to optimize PIC formation. The remarkable difference in charge density and rigidity of HA and AL did not have a significant influence on the formation of PICs. PICs with small size (diameter of about 50-80 nm) and low polydispersity were obtained up to 5 mg/mL of polymer. After cross-linking with l-lysine ethyl ester, the nanoreactors were dissociated by adding NaCl. The nanogels were easily purified and isolated by dialysis. The dissociation of the nanoreactors and the formation of the nanogels were confirmed by 1H NMR, DLS, TEM and ζ-potential measurements. The size of the smallest nanogels in solution in the swollen state was 50-70 nm in presence of salt and 80-100 nm in water. © 2013 Elsevier Ltd. All rights reserved.

Water-soluble gold nanoparticles functionalized by sodium 3-mercapto-1-propansulfonate (Au-3MPS) were synthesized with different Au/thiol molar ratios for their ability to interact with biomolecules. In particular, a synthetic glucocorticoid steroid, i.e. dexamethasone (DXM) was selected. Herein, the formation of the Au-3MPS/DXM bioconjugate is reported. Au-3MPS nanoparticles show a plasmon resonance at 520 nm, have a spherical morphology and average size of 7–10 nm. The total number of gold atoms was estimated to be about 10600, with a surface component of 8800 atoms and a number of thiol ligands of about 720, roughly one anchored thiol every 10 surface gold atoms. The drug-nanoparticle interaction occurs through the fluorine atom of DXM and Au(I) atoms on the gold nanoparticle surface. The 3MPS ligands closely pack apart each other to leave room for the DXM, that lies at the gold surface in an unusual, almost parallel feature. The loading efficiency of DXM on Au-3MPS was assessed in the range 70–80%, depending on the thiol content. Moreover, our studies confirmed the drug release of about 70% in 5 days. Thanks to their unique properties, i.e. high water solubility, small size and almost monodispersity, Au-3MPS display high potential in biotechnological and biomedical applications, mainly for the loading and release of water insoluble drugs.

The dielectric and conductometric spectra of water-in-oil microemulsions below percolation in the frequency range from 1 MHz to 1.8 GHz have been analyzed on the basis of the electrical modulus formalism. In the frequency range investigated, this approach clearly evidences the presence of a particular polarization mechanism, resulting in a well-defined dielectric dispersion, located between that due to the orientational polarization of the bulk aqueous phase and that due to the ionic structure of the interface, usually occurring in heterogeneous systems. This polarization mechanism has been attributed to the "in-phase" correlation displacement of surfactant polar head groups surrounding each water droplet dispersed in the oil phase. This mechanism differs from the usual interfacial Maxwell-Wagner effect. The advantage of the electrical modulus formalism, in comparison with the analysis of the directly measured quantities, the permittivity epsilon'(omega), and the total electrical conductivity sigma(omega), are briefly discussed. Copyright 2001 Academic Press.

The molecular conformation and the behaviour of stereoregular polyphenylacetylene (PPA), prepared by catalytic polymerization in the presence of a Rh(I) complex and dissolved in three different organic solvents (tetrahydrofuran (THF), toluene and chloroform), have been studied by means of static and dynamic light scattering measurements. The results have been compared with those obtained from UV–VIS measurements carried out on the same systems. A very complex phenomenology appears. In THF, the polymer molecular weight, M w , increases with time, remains approximately constant in toluene and decreases in chloroform. On the contrary, the hydrodynamic radius, R H , maintains constant at a value of about 270 nm in THF, while in toluene and chloroform a steady-state condition is reached after 500–1000 min, with a value of the hydrodynamic radius of the order of 150–200 nm. These results suggest that each solvent produces a different effect on the pristine structure of PPA. THF induces the entanglement of the polymer chain and an apparent higher molecular weight, toluene promotes a structural modification, probably a narrow helicoidal red form and chloroform leads to both isomerization and degradation.

The interactions among five different gangliosides (three monosialogangliosides GM1, GM2. GM3 and two disialogangliosides GDla and GDlb) in mixed monolayers with dipalmitoylphosphatidylcholine [DPPC] were investigated at the air-water interface by means of surface pressure measurements. The surface pressure-area isotherms have been obtained on aqueous substrates at an ionic strength 0.145 M NaCl, pH=7.2, at a temperature of 20°C. Excess Gibbs energies of mixing in the monolayers have been calculated as a function of composition and surface pressure. Deviation from ideality denotes a different molecular organization of monosialogangliosides and disialogangliosides, indicating changes in their molecular arrangement in phospholipid monolayers due to different polar head group interactions. The possible significance of these observations is discussed in relation to ganglioside organization in biological cell membranes.

The dielectric and conductometric properties of mixed ganglioside/phospholipid vesicle aqueous suspensions were measured in the frequency range from 10 kHz to 10 MHz, where a pronounced dielectric dispersion due to surface bilayer polarization occurs. The concentration of the ganglioside employed, a disialoglycosphingolipid GD1a, was varied from 50 to 500 μg/mL (corresponding to a molar ratio [GD1a]/[DPPC] from 0.2 × 10-3 to 2 × 10-3) and the excess surface polarizability, attributed to ganglioside organization within the lipid bilayer, was evaluated. The dependence of the ganglioside concentration shows that a clusterization process occurs, giving rise to the formation of large in-phase aggregates whose coordination number, of the order of a few hundred dipoles, depends on temperature. The relevance, from a biological point of view, of a nonuniform distribution of GD1a in a lipid bilayer membrane is briefly discussed.