Microheterogeneous Media Research Articles

A preliminary study on the application of the two-space nonperiodic asymptotic homogenization method to the EEG forward problem with continuously differentiable coefficient

The knowledge on the Electroencephalogram (EEG) forward problem is important to improve the imaging of the neural activity, that is an inverse problem. This paper introduces the study of the EEG forward problem via a nonperiodic homogenization technique: the two-space method. Considering a concentric spheres head model for the brain-skull-scalp medium as an micro-heterogeneous medium, a simplification consisting of a 1D problem in spherical coordinates with continuously differentiable coefficient is considered. The two-space method is applied successfully, and a numerical example shows the convergence of the micro-heterogeneous solution to the one obtained by the two-space method, as was expected. The preliminary conclusion is that this approach for the EEG forward problem with homogenization techniques shows itself as very promising. More experiments should be executed, considering more realistic models for the head.

A Simple Live Cell Imaging "Turn-On" Fluorescence Probe for the Selective and Sensitive Detection of Aqueous Hg2+ Ions.

A simple, efficient, and reversible fluorescent sensor probe, PBA (2,6-dimethyl pyrone barbituric acid conjugate), comprised of a pro-aromatic donor conjugated with a barbituric acid, was developed for the detection of highly toxic mercuric ions. The probe showed high selectivity and "Turn-On" fluorescence response towards Hg2+ among various metal cations such as Na+, Mg2+, Ca2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Ba2+, Hg2+, and Pb2+, in both homogeneous and microheterogeneous micelle medium sodium dodecyl sulphate (SDS). The binding stoichiometry, limit of detection (LOD), and binding constant for the PBA-Hg complex were determined. The mechanism of binding was ascertained using the N,N'-dimethylbarbituric acid conjugate of 2,6-dimethylpyran (PDMBA), where no binding interaction by deprotonation is possible. In the presence of cysteamine hydrochloride and trifluoroacetic acid (TFA), the complexation of Hg2+ with PBA was demonstrated to be reversible, indicating its potential for the development of reusable sensors. Moreover, the practical applicability of PBA in monitoring Hg2+ in living cells was also evaluated.

‘On and Off’ intercalative binding behaviour of double chain surfactant cobalt(III) complex containing 2, 2′-bipyridyl ligand in β-Cyclodextrin: A detail approach on Host-guest inclusion of surfactant cobalt(III) complex and CT-DNA binding in micro-heterogeneous medium

The binding interaction of surfactant cobalt(III) complex, cis-[Co(bpy)2(HA)2](ClO4)3, in which bpy is 2,2-bipyridine and HA is hexadecylamine or cetylamnine with DNA was through intercalative mode via the long aliphatic chains present in the ligands. The binding was investigated by various techniques, electronic absorption, fluorescence spectroscopy, circular dichroism (CD), cyclic voltametry (CV) and viscosimetry measurements. The spectroscopic studies together with cyclic voltammetry and viscosity experiments support that the surfactant cobalt(III) complex binds to calf thymus DNA by intercalation through the aliphatic chain present in the complex into the base pairs of DNA. The presence of bipyridine ligand with larger π-frame work may also enhance intercalation. UV–vis., spectrum showed 4 nm bathochromic shift of the absorption band at 352 nm along with significant hypochromicity for the absorption band of the complex. The intrinsic binding constants(at below and above CMC are Kb = 2.41 × 105M−1, Kb = 3.12 × 106M−1 respectively) is more in keeping with intercalators and suggests this binding mode. The viscosity measurements showed that the surfactant cobalt(III) complex-DNA interaction can be hydrophobic and confirm intercalation. Moreover, the complex induced detectable changes in the CD spectrum of CT-DNA. Competitive binding study with ethidium bromide (EB) shows that the surfactant complex exhibits the ability to displace the DNA-bound EB indicating that the complex binds to DNA in strong competition with EB for the intercalative binding site. Also, CV results confirm this mode because, with increasing the CT-DNA concentration, shift to higher potential was observed. Besides the effect of binding of surfactant cobalt(III) complex to DNA in presence of β-cyclodextrin has also studied. This binding of the surfactant cobalt(III) complex in presence of β-cyclodextrin medium has been prevented (at below and above CMC are Kb = 5.45 × 104M−1, Kb = 6.92 × 105M−1 respectively) due to the incorporation of the aliphatic chains into the cavity of β-cyclodextrin. In presence of β-cyclodextrin the binding occur through surface and (or) groove binding can be attributed to the inclusion of the long aliphatic chain that is present in one of the ligands into cyclodextrin.

Picosecond to Second Fluorescence Correlation Spectroscopy for Studying Solute Exchange and Quenching Dynamics in Micellar Media.

Numerous studies have been devoted to understand the reaction kinetics in micelles, where the accessible kinetic time window is often limited by the dynamic range of the employed spectroscopic technique. This is usually accompanied by a selection of probes that comfortably explore time scales where slow solute exchange kinetics is negligible, as compared to the fast excited state reactions. This has led to an undervaluation of the role played by dynamic partitioning of hydrophilic solutes in microheterogeneous media. Here, we employ fluorescence correlation spectroscopy (FCS) and the zwitterionic dye Rhodamine 110 to quantitatively explore the impact of solute exchange on the photoinduced electron transfer between this dye and N,N-dimethylaniline in micellar media. Our study elucidates the coupling and interplay between the kinetics of photophysics, quenching, and solute exchange through a quantitative unified molecular-state quenching-kinetic model that describes the steady-state ensemble and FCS data from subnanosecond photon antibunching to millisecond diffusions.

Redox Cycling within Nanoparticle-Nucleated Protein Superstructures: Electron Transfer between Nanoparticulate Gold, Molecular Reductant, and Cytochrome c.

We previously described how thousands of the heme protein cytochrome c (cyt.c) self-organize into multilayered, roughly spherical superstructures as initiated by nucleation around one colloidal gold or silver nanoparticle. Within these superstructures, the protein is stabilized to unfolding in buffered media and survives superstructure encapsulation within silica gels and processing to form bioaerogels. We now report that Au∼cyt.c superstructures in buffered media are not simply static groupings of proteins, but that the Au core and protein corona exhibit dynamic electron-transfer reactions within the superstructure as verified by UV-visible and resonance Raman spectroscopy. Within the superstructure, hundreds to thousands of ferricytochrome c (FeIII-cyt.c) are reduced to ferrocytochrome c (FeII-cyt.c) following first-order kinetics with an average apparent forward rate constant of 1.9 ±0.4 × 10-5 s-1. The reducing power in the microheterogeneous medium is derived from two multielectron reductants: tannic acid used to stabilize the commercial gold sol and the Au nanoparticle at the center of the protein superstructure. Fluorescence monitoring of guanidinium chloride-induced unfolding reveals that superstructure-associated cyt.c is stabilized to unfolding before and after chemical reduction of FeIII-cyt.c to form FeII-cyt.c, indicating that the superstructures remain intact during microheterogeneous redox reactions. Smaller nucleating Au nanoparticles or lower ionic strength in the buffered medium yields a greater extent of cyt.c reduction. Partial oxidation of the cyt.c-associated nanoparticulate Au is verified by X-ray photoelectron spectroscopy. The Au nanoparticle at the heart of the superstructure functions as a direct electron donor to the heme with oxidized Au atoms being recycled back to Au(0) as long as residual tannic acid, derived from the Au sol mother liquor, is present in the aqueous microheterogeneous medium.

Riboflavin sensitized photodegradation of Furaneol in a β-cyclodextrin complex

A study on the photodegradation of the widely employed flavoring compound Furaneol (FUR), in the presence of vitamin B2 (Riboflavin, Rf) was carried out, in aqueous and microheterogeneous media. The system as a whole allows the evaluation of FUR stability, since the vitamin is an endogenous natural photosensitizer. In a visible-light-irradiated solution of Rf plus FUR, a complex mechanism of competitive reactions occurs. FUR quenches the singlet (2.7 × 109 M−1s−1) and triplet (6.0 × 108 M−1s−1) Rf electronically excited states and reacts with singlet molecular oxygen (O2(1Δg)) generated from the triplet excited state of the sensitizer, with a reactive rate constant of 1.97 × 107 M−1s−1. In the oxidation process, two oxygen molecules are incorporated. In the presence of β-cyclodextrin (βCD), experimental and theoretical results show the formation of an inclusion 1:1 complex of FUR with the oligosaccharide. The Rf- photosensitized oxidation rates of FUR were higher in the microheterogeneous medium, probably due to the incorporation of FUR in the non-inclusion complex between Rf and βCD which may produce O2(1Δg) near the oxidizable substrate. The overall result of this study demonstrates that visible-light exposure of formulations containing Rf and FUR may cause significant oxidation of the flavoring agent.

Direct Irradiation of Phenol and Para-Substituted Phenols with a Laser Pulse (266 nm) in Homogeneous and Micro-heterogeneous Media. A Time-Resolved Spectroscopy Study

Direct irradiation of para-substituted phenols under N2 atmosphere in homogeneous (cyclohexane, acetonitrile, and methanol) and micellar (SDS) solution was investigated by means of time-resolved spectroscopy. After a laser pulse (266 nm), two transient species were formed, viz. the para-substituted phenol radical-cations and the corresponding phenoxy radicals. The radical-cations showed a broad absorption band located between 390 and 460 nm, while the phenoxy radicals showed two characteristic bands centered at 320 nm and 400-410 nm. The deprotonation rate constant of radical-cations (kH) of 105 s-1 and the reaction rate constant of the phenoxy radicals (kR) in the order of 109-1010 M-1·s-1 have been derived. The kH rate constants gave good linear Hammett correlation with positive slope indicating that electron-withdrawing substituents enhance the radical-cation acidity. The binding constants (Kb) of the para-substituted phenols with the surfactant were also measured, and NOESY experiments showed that phenols were located in the hydrophobic core of the micelle. Finally, computational calculations provided the predicted absorption spectra of the transients and nice linear correlations were obtained between the theoretical and experimental energy of the lower absorption band of these species.

Fast, Light-Responsive, Metal-Like Polymer Actuators Generating High Stresses at Low Strain

Summary Producing lightweight polymeric actuators able to generate high stresses typical of hard metals and/or ceramics remains challenging. The photo-mechanical responses of ultra-drawn ultra-high molecular weight polyethylene (UHMWPE) actuators containing azobenzene photo-switches with symmetrically attached polyethylene (PE) side chains are reported. Long PE side chains promote dispersion within the apolar UHMWPE matrix, and the ultra-drawn films are highly aligned. The ultra-drawn azobenzene-doped UHMWPE films have high Young's moduli (∼100 GPa) and are viscoelastic at room temperature at strains below 1%. The photo-mechanical response of the films is fast ( 6 × 104 Pa (kg m−3)−1) to UV or visible light at a low strain (∼0.06%). The actuator responds to rotating linearly polarized light, causing a photo-induced stress wave response. Such rapid, high-stress, low-strain, photo-mechanical responses are unique in soft polymer systems with physical values approaching hard metals/ceramics.

Understanding the intrinsic fluorescence of piperine in microheterogeneous media: partitioning and loading studies

Piperine, an ingredient of black pepper, is widely used in pharmaceutical applications.

Excited state proton transfer based fluorescent molecular probes and their application in studying lipid bilayer membranes.

Molecules with ionizable protons, with different proton transfer efficiencies in the excited and ground states, show excited state prototropism (ESPT). In suitable proton donating/accepting environments, ESPT of a molecule can result in the observation of emissions from different prototropic species, each characterized by different emission spectra and different emission lifetimes. In condensed media, the immediate environment around the ESPT molecule can significantly influence the emission spectral parameters of different prototropic species. This forms the basis of ESPT based fluorescence sensing. The concept of ESPT has been widely used for probing dynamical and structural information of micro-heterogeneous media like micelles, polymers, lipid bilayer membranes, etc. ESPT molecules like naphthol and intra-molecular ESPT (ESIPT) molecules like hydroxyflavones etc., are said to be good multi-state fluorescent molecular probes if (i) the partitioning of these molecules to a micro-heterogeneous organized medium is more efficient, and (ii) the molecules possess distinct excitation and emission wavelengths corresponding to their different prototropic forms. The fluorescence of different prototropic forms shows a sensitive response towards the change in the local environment around the micro-heterogeneous organized medium concerning the physical properties, local structure, and dynamics. This review mainly comprises the work carried out on ESPT fluorescence molecular probing of biomimetic liposomes/lipid bilayer membranes from 1990 onwards.

Crown- and phosphoryl-containing metal phthalocyanines in solutions of poly(N-vinylpyrrolidone): Supramolecular organization, accumulation in cells, photo-induced generation of reactive oxygen species, and cytotoxicity

Nowadays, the study of well-known sensitizers for photodynamic therapy and search for new ones are intensively conducted. In the present work supramolecular organization of crown-ether and phosphoryl-containing phthalocyanines ({Mgcr8Pc, I, and М[R4Pc] (M = Zn2+, R = -OPhP(O)(OH)(OC5H11), II; M = 2H+, R = -OPhP(O)(OH)(OC5H11), III; M = 2H+, -OPhP(O)(OH)2), IIIa}, respectively) was studied in microheterogeneous media. The role of a metal ion of a macrocycle in monomerization of phosphoryl-containing Pc in the presence of water-soluble poly(N-vinylpyrrolidone) was revealed. Some photobiological properties of compound I as possible photosensitizer with respect to human adenocarcinoma cells, HeLa, were analyzed. So, the light and dark cytotoxicity of I (IC50 dose) was 1.83 μМ and higher than 25 μМ, respectively. The reactive oxygen species (ROS) formation studied with use of fluorescent ROS detector DCFH2 revealed the plateau on the curves of fluorescence intensity vs time after 30 min of irradiation and ROS are almost not produced after the end of irradiation. In HeLa cells, accumulation of compounds I and II as well as fluorescent DCF presence were shown by confocal microscopic images. At concentration of 5 μM, compound I easily penetrates into the cell localizing primarily in the perinuclear region, whereas compound II mainly remains in the periphery of the cells in the fluorescent-active state. The results obtained allow us to continue the study of these interesting compounds.

Expulsion of a potent cancer-cell photosensitizer from its micelle-bound state using β-cyclodextrin: A tenable model for efficient drug release.

The present study delves into the interaction of a potent cancer-cell photosensitizer Norharmane (NHM) with non-ionic triblock copolymer P123, followed by the assessment of the stability of the formed complex in the presence of β-cyclodextrin (β-CD). Spectroscopic results unveil the modulation of the prototropic equilibrium of NHM within the constrained microheterogeneous medium of the copolymer micelle to be favoured towards the neutral species of NHM over the cationic counterpart; which has been aptly rationalized invoking the key role of hydrophobic interaction in the association process and is further reinforced from steady-state and time-resolved spectroscopic measurements. The micropolarity of the probe-binding site has been evaluated by the archetypal ET(30) analysis revealing that the cationic probe remains in the corona region of the micelle instead of penetrating deeper into the micellar core. Moreover, the effect of β-CD on the stability of the NHM-bound P123 aggregates has also been investigated, revealing that β-CD can be used as a potential host for the release of the micelle-encapsulated drug through an inclusion complex formation with the P123 monomers. The result is expected to be of potential interest from medical perspective owing to the context of efficient drug release at their potential sites.

A Detailed Microscopic Insight into the Aggregation Behaviors of Doxorubicin Hydrochloride in Different Microheterogeneous Media

In recent time periods, a large portion of research interests include the study of aggregation properties of different amphiphilic molecules and the resulting morphological architectures due to their significant applications in diverse research fields. The aggregation behaviors of different biomolecules are also very much important and thus recently become the cup of tea to a large number of research communities. In this respect, the aggregation result of potentially important chemotherapeutic molecule, doxorubicin hydrochloride (Dox) in a conventional imidazolium based surface active ionic liquid (SAIL), 1-octyl-3-methylimidazolium chloride (C8mimCl) was studied in details. The complete characterizations using dynamic light scattering (DLS), different microscopic techniques like fluorescence lifetime imaging microscopy (FLIM), transmission electron microscopy (HR-TEM and analytical TEM), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) with fourier-transform infrared spectroscopy (FTIR) measurements revealed the formation of large spherical vesicular Dox/C8mimCl aggregates. The guiding forces behind such SAIL induced aggregation of Dox were also explored. Finally a common bile salt, sodium cholate (NaCh) was observed to transform Dox/C8mimCl spherical aggregates to rod like fibrillar aggregates. In summary, the aggregation of Dox in microheterogeneous medium of C8mimCl SAIL to spherical vesicular aggregates and also the bile salt induced disruption into rod like fibrillar aggregates were studied in detail. The formation and disruption of Dox forming vesicular aggregates can be modeled as a new generation future delivery system for biologically important molecules with smart loading and release phenomena where the biomolecule itself aggregates to form the delivery system.

The location of amphiphobic antioxidants in micellar systems: The diving-swan analogy

A protocol for determining the location of antioxidants (AOs) in a micro-heterogeneous medium was applied to three series of AOs with increasing hydrophobicities: chromancarboxylic acid (“Trolox”) esters, caffeic acid and its esters, and gallic acid and its esters. The observed paradoxical behaviour of these and other commonly encountered antioxidants was rationalized with the aid of a pictorial simile, the “diving-swan” analogy, that explains the orientation and location of an amphiphobic AO when it reacts with a radical probe in the micellar interface.

Supramolecular organization of crown- and phosphoryl-containing magnesium and zinc phthalocyaninates in solutions of synthetic and natural surfactants

The behavior of crown- and phosphoryl-containing magnesium and zinc phthalocyaninates in solutions of synthetic and natural surfactants is studied. In a phosphate buffer (рН 7.4), zinc phthalocyaninate bearing oxy(pentyloxy)phosphoryl groups in peripheral substituents of the macrocycle is in aggregated state. According to absorption and fluorescence spectroscopy data, adding oppositely charged synthetic and natural surfactants leads to monomerization of this compound. The degree of monomerization of magnesium octa[(4´-benzo-15-crown-5)oxy]-phthalocyaninate in a microheterogeneous medium is affected by the concentration of sodium cholate and ionic strength. Fluorescence-active supramolecular gels based on sodium deoxycholate were prepared using phosphoryl-containing zinc phthalocyaninate.

Explicit computational wave propagation in micro-heterogeneous media

Explicit time stepping schemes are popular for linear acoustic and elastic wave propagation due to their simple nature which does not require sophisticated solvers for the inversion of the stiffness matrices. However, explicit schemes are only stable if the time step size is bounded by the mesh size in space subject to the so-called CFL condition. In micro-heterogeneous media, this condition is typically prohibitively restrictive because spatial oscillations of the medium need to be resolved by the discretization in space. This paper presents a way to reduce the spatial complexity in such a setting and, hence, to enable a relaxation of the CFL condition. This is done using the Localized orthogonal decomposition method as a tool for numerical homogenization. A complete convergence analysis is presented with appropriate, weak regularity assumptions on the initial data.

Effective electromagnetic properties of microheterogeneous materials with surface phenomena

In this paper, we present an approach to calculate the complex dielectric permittivity of a micro-heterogeneous medium composed of non-conductive solid inclusions embedded into the conductive liquid continuous host. To take into account the surface effects, we approximate the inclusion by a layered ellipsoid consisting of a dielectric core and an infinitesimally thin outer shell corresponding to an electrical double layer (EDL). To predict the effective complex dielectric permittivity of materials with a high concentration of inclusions, we have modified the Effective Field Method (EFM) for the layered ellipsoidal particles with complex electrical properties. We present the results of complex permittivity calculations for the composites with randomly and parallel oriented ellipsoidal inclusions. To analyze the influence of surface polarization, we have accomplished modeling in a wide frequency range for different existing physic-chemical models of double electrical layer. The results obtained show that the tensor of effective complex permittivity of a micro-heterogeneous medium with surface effects has complicate dependences on the component electrical properties, spatial material texture, and the inclusion shape (ellipsoid aspect ratio) and size. The dispersion of dielectric permittivity corresponds to the frequency dependence for individual inclusion of given size, and does not depend on the inclusion concentration.

A simple cost effective carbazole–thiobarbituric acid conjugate as a ratiometric fluorescent probe for detection of mercury(ii) ions in aqueous medium

A multimode ratiometric Hg2+ selective chemosensor based on a carbazole–thiobarbituric acid conjugate was developed. It responds to the presence of Hg2+ by colorimetry and by fluorescence. The sensor action is demonstrated in both aqueous homogeneous or microheterogeneous media.

Effect of the binding interaction of an emissive niacin derivative on the conformation and activity of a model plasma protein: A spectroscopic and simulation-based approach

The present work demonstrates a detailed photophysics of bio-active drug-like acid viz., 2-hydroxynicotinic acid (2-HNA) and its interaction with a model plasma protein Bovine Serum Albumin (BSA). The drug which is in essence a vitamin-B3 derivative, is capable of exhibiting ultrafast lactim-lactam cross-over response and thereby the modulation of the lactam emission within the bio-environment of the protein has been depicted spectroscopically to reveal the drug-protein interaction. Apart from evaluating the binding constant, the probable location of the neutral drug molecule within the protein cavity (hydrophobic subdomain IIIA) has been explored by AutoDock-based blind docking simulation technique. In this microheterogeneous medium, slow solvent reorientation time with respect to the emissive lifetime of the drug explicate the Red Edge Effect (REE). To complement the findings about the binding process, chaotrope-induced protein denaturation has also been inspected. The probe also illustrates a perceptible difference in rotational relaxation time in confined medium than in aqueous medium which strengthen our verdict. Unfolding of the protein in the presence of the drug molecule has been probed by the decrease of the α-helical content, obtained via circular dichroism (CD) spectroscopy, which is also supported by the gradual slaughter of the esterase activity of the protein in the presence of the drug molecule.

1,3,4-Oxadiazole Derivatives. Optical Properties in Pure and Mixed Solvents.

1,3,4-Oxadiazole derivatives-organic materials are an interesting and continuously developing area of research. This review describes some optical properties and highlights the current applications of these compounds in biomedical and optoelectronic fields. The relationships between polymer structures, environmental factors and optical properties (absorption and fluorescence) of several selected and relevant l,3,4-oxadiazole-containing molecules were presented in this review. These aspects were analyzed in various pure solvents and microheterogeneous media (mixed solvents). Also, the selectivity and sensitivity of some 1,3,4-oxadiazole derivatives-organic materials for different metal ions were discussed and evaluated by using spectral techniques. Finally, some important photophysical characteristics of 34 series of organic materials containing -1,3,4-oxadiazole rings, were collected in a table.