AFM study of the stability of a dense affinity-bound liposome layer

Liposomes that are surface-bound to a biomaterial such as a contact lens are of interest for localized delivery of therapeutic agents, but it is not known whether such liposome layers are sufficiently robust. The stability of a dense, PEG-functionalized layer of liposomes, affinity-bound onto a multilayer coated surface, was tested under various stress conditions using colloid-probe atomic force miscroscopy (AFM). The different stress effects were generated by varying the applied normal load of the probe and the impinging fluid shear through different approach velocities and by varying the applied lateral forces by scanning under increasing force loads. The effect of applied forces (normal and lateral) was further investigated by coating the probe with a layer of albumin. The liposomes remained intact following the ramping of both protein-coated and uncoated probes under the normal and lateral loads. The low-fouling nature of these liposomes, with respect to nonspecific protein adsorption, was also demonstrated from the interaction force measurements which showed only weak adhesion from the protein layer during the contact period of the albumin-coated probe. The observed adhesive interactions were concluded to be a direct result of the applied load from the probe, during the force measurements, rather than from attraction of the protein molecules for the surface-bound liposomes. The low frictional response of the liposome layer indicated the viscoelastic nature of these molecules, which enabled liposome structure retention during the continuous load application. The demonstrated stability of the liposomes presents a system of viable and localized drug delivery in, for example, ophthalmic applications.     

Solid-state stability and kinetic study of three glucocorticoid hormones: prednisolone,prednisone and cortisone

Journal of Thermal Analysis and Calorimetry - In the class of steroid hormones, glucocorticoids are belonging to the subclass of corticosteroids, consisting of numerous synthetic or naturally...     

Effect of secondary structure on the self-assembly of amphiphilic molecules: a multiscale simulation study

The self-assembly of amphiphilic molecules is of interest from a fundamental and practical standpoint. There has been recent interest in a class of molecules made from β-amino acids (which contain an additional backbone carbon atom when compared with natural amino acids). Block copolymers of β-peptides, where one block is hydrophobic and the other is hydrophilic, self-assemble into micelles. In this work, we use computer simulations to provide insight into the effect of secondary structure on the self-assembly of these molecules. Atomistic simulations for the free energy of association of a pair of molecules show that a homochiral hydrophobic block promotes self assembly compared to a heterochiral hydrophobic block, consistent with experiment. Simulations of a coarse-grained model show that these molecules spontaneously form spherical micelles.     

Gemini amphiphilic pseudopeptides: synthesis and preliminary study of their self-assembling properties

The synthesis of a family of Gemini Amphiphilic Pseudopeptide (GAP) molecules by a reductive amination reaction has been carried out. The process is highly modular and can be efficiently performed with different pseudopeptidic diamines as well as aliphatic and aromatic aldehydes. Preliminary studies showed the abilities of the GAPs to self-assemble into supramolecular nanostructures.     

Synthesis of amphiphilic phenylazophenyl glycosides and a study of their liquid crystal properties

Several 4-(4'-N,N-didodecylaminophenylazo)phenyl 1,2-trans glycosides 5a-e with various carbohydrate heads (beta-D-gluco, beta-D-galacto, beta-lacto, beta-D-xylo, and alpha-D-manno) have been synthesized. The key step was the formation of phenyldiazonium tetrafluoroborates 2a-e from the per-O-acetylated 4-aminophenyl glycosides 1a-e. These salts were condensed with N,N-didodecylaniline under phase transfer conditions and the per-O-acetylated 4-(4'-N,N-didodecylaminophenylazo)phenyl 1,2-trans glycosides 4a-e were fully de-O-acetylated by the Zemplén method. The self-organizing liquid crystal properties of the compounds were investigated by a variety of techniques, including polarized light microscopy, differential scanning calorimetry, and X-ray diffraction. All but one of the materials exhibited smectic A, lamellar phases. Remarkably, the glucose derivative exhibited a rectangular disordered columnar phase. This result has implications with respect to the induced curvature created by the recognition processes of the glucose headgroup relative to the other sugar moieties and to the prevalence of various glycolipids in cell membranes     

Effect of the molecular structure of more common amphiphilic molecules on their interactions with dioleoyl-phosphatidylcholine monolayers

A large number of surface-active or amphiphilic compounds interact with biological membranes and their various models. The surface-active properties of these compounds have been cited as a fundamental factor which determines the tendency of these molecules to bind to, to cross and to perturb the lipid structure of biomembranes and biomembranes models. As well as surface activity, the extent of interaction of a compound with a membrane has been correlated with its lipophilicity. This study shows that the surface activity and lipophilicity of a compound are not the only factors which determine its interaction with a lipid membrane structure. Experiments have been carried out looking at the effect of compounds of different molecular structure on their type of association with self-assembled phospholipid monolayers on mercury electrodes. The paper concludes by demonstrating the properties of different compounds which facilitate their interaction with the supported lipid monolayer.     

Effect of chain lengths of PEO-PPO-PEO on small unilamellar liposome morphology and stability: an AFM investigation

The morphology and stability of small unilamellar egg yolk phosphatidylcholine (EggPC) liposomes modified with the Pluronic copolymer (poly (oxyethylene)-poly (oxypropylene)-poly (oxyethylene) (PEO-PPO-PEO)) with different compositions on mica surface have been investigated using atomic force microscopy. Morphology studies reveal significant morphological changes of liposomes upon incorporating the Pluronic copolymer. Bilayers are observed for Pluronic with small hydrophilic (PEO) chain lengths such as L81 [(PEO)2(PPO)40(PEO)2] and L121 [(PEO)4(PPO)60(PEO)4]; bilayer and vesicle coexistence is observed for P85 [(PEO)26(PPO)39.5(PEO)26] and F87 [(PEO)61.1(PPO)39.7(PEO)61.1]; and stable vesicles are observed for F88 [(PEO)103.5(PPO)39.2(PEO)103.5], F127 [(PEO)100(PPO)65(PEO)100], and F108 [(PEO)132.6(PPO)50.3(PEO)132.6]. The micromechanical properties of Pluronic-modified EggPC vesicles were studied by analyzing AFM approaching force curve. The bending modulus (k(c)) of the Pluronic-modified EggPC vesicles increased several-fold compared with that of the pure EggPC vesicles. The significant difference is due to the enhanced rigidity of the EggPC vesicles as a result of the incorporation of PPO molecules and PEO chains. Based on the analysis of onset point by AFM and diameters of vesicles by light scattering, it was concluded that the favorable model to describe the polymer-bilayer interaction is the membrane-spanning model.     

Liposomal drugs dispersed in hydrogels. Effect of liposome, drug and gel properties on drug release kinetics

Release of calcein and griseofulvin (GRF) from control (gels in which solutes are dissolved in) and liposomal gels was studied using agarose-assisted immobilization as a technique to separate gels from drug-receptor compartments. Liposomes composed of phosphatidylcholine (PC) or distearoyl-glycero-PC and cholesterol (DSPC/Chol), and incorporating calcein or GRF were prepared by thin film hydration. After cleaning the liposomes they were dispersed in different hydrogels (carbopol 974 [1, 1.5 or 2% (w/w)], hydroxylethyl-cellulose (HEC) [4% (w/w)], or a mixture of the two), and release of calcein or GRF was followed by fluorescence or photometric technique, respectively. Results show that calcein release from liposomal gels is slower compared to control gels, and can be further retarded by using rigid-membrane liposomes (faster release from PC-liposome compared to DSPC/Chol-liposome gels). Additionally, calcein release is not affected by the lipid amount loaded (in the range from 2 to 8 mg/ml), therefore solute loading can be controlled according to needs.

Oppositely, GRF release from liposomal gels is determined by drug loading. At high drug loading levels (compared to GRF aqueous solubility), GRF is released with constant rate from liposomal gels irrespective of liposome type (PC or DSPC/Chol). Thereby, for amphiphilic/lipophilic drugs, drug properties (solubility, log P) determine the system behavior.

Calcein and GRF release from control carbopol gels is faster compared to HEC and mixture gels. The same is true for calcein in liposomal gels. Carbopol gel rheological properties were found to be significantly different (compared to the other gels), implying that these characteristics are important for drug diffusion from gels.     

Influence of amphiphilic structures on the stability of polyphenols with different hydrophobicity

Autooxidation of five polyphenols representing range of different hydrophobicities(catechin gallate (CG),(-)catechin((-)C),epicatechin(EC),epigallocatechin gallate(EGCG)and epigallocatechin(EGC)) in three different aqueous solutions:molecular solution,micellar solution(Tween-20)and liposomal dispersion(soybean lecithin)was monitored by HPLC.The rate of oxidation of the five polyphenols was higher at pH 4.5 than at pH 3.5.Compared with the control,addition of Tween-20(micellar structure)and lecithin(liposomal structure)significantly decreased the degradation of polyphenols.In the presence of lecithin the autooxidation of all the five polyphenols was slower than in the presence of Tween-20. The effective protection of the colloidal structures was compared with the hydrophobicity of the poly- phenols estimated from the partitioning between octanol and water.The protection from oxidation in the presence of the colloidal structures(micellar or liposomal)increased with increasing partitioning of a polyphenol towards the hydrophobic environment.The protecting effect of the colloidal structures was more effective at pH 4.5 than at pH 3.5.     

Efficacy of cosmetic formulations containing dispersion of liposome with magnesium ascorbyl phosphate, alpha-lipoic acid and kinetin

The present study aimed to evaluate the photoprotective effects of cosmetic formulations containing a dispersion of liposome with magnesium ascorbyl phosphate (MAP), alpha-lipoic acid (ALA) and kinetin, as well as their effects on the hydration and viscoelastic skin properties. The photoprotection was determined in vitro (antioxidant activity) and in vivo on UV-irradiated hairless mouse skin. The hydration effects were performed with the application of the formulations under study on the forearm of human volunteers and skin conditions were analyzed before and after a single application and daily applications during 4 weeks in terms of transepidermal water loss (TEWL), skin moisture and viscoelastic properties. The raw material under study possessed free-radical scavenging activity and the formulation with it protected hairless mouse skin barrier function against UV damage. After 4 weeks of application on human skin, the formulation under study enhanced stratum corneum skin moisture and also showed hydration effects in deeper layers of the skin. Thus, it can be concluded that the cosmetic formulation containing a dispersion of liposome with MAP, ALA and kinetin under study showed photoprotective effects in skin barrier function as well as pronounced hydration effects on human skin, which suggests that this dispersion has potential antiaging effects.     

Effect of the electrostatic charge on the mechanism inducing liposome solubilization: a kinetic study by synchrotron radiation SAXS

The anionic surfactant sodium dodecyl sulfate (SDS) was used to induce the initial steps of the solubilization of liposomes. The structural transformations as well as the kinetics associated with this initial period were studied by means of time-resolved small-angle X-ray scattering (SAXS) using a synchrotron radiation source. Neutral and electrically charged (anionic and cationic) liposomes were used to investigate the effect of the electrostatic charges on the kinetics of these initial steps. The mechanism that induces the solubilization process consisted of adsorption of surfactant on the bilayers and desorption of mixed micelles from the liposomes surface to the aqueous medium. In all cases the time needed for desorption of the first mixed micelles was shorter than that for complete adsorption of the surfactant on the liposomes surface. The present work demonstrates that adsorption of the SDS molecules on negatively charged liposomes was slower and release of mixed micelles from the surface of these liposomes was faster than for neutral liposomes. In contrast, in the case of positively charged liposomes, the adsorption and release processes were, respectively, faster and slower than those for neutral vesicles.     

Effect of the soil uses on their thermal stability

Differential scanning calorimetry was applied to assess on seasonally soil organic matter changes. Soils were collected in two sites located in Viveiro (Galicia, Spain). One of them has been used as arable land and the other one was under pinewood. Soil samples were seasonally collected during a year. The heat of combustion and the ignition temperature of the soil organic matter were calculated by analyzing the thermograms obtained by differential scanning calorimetry. The shape and the maximum and end temperatures of the two exothermic peaks observed in the thermograms, yielded information about the relations between the labile and recalcitrant pools, and hence information about carbon stabilization degree in both soils.     

Effect of curcumin on liposome: curcumin as a molecular probe for monitoring interaction of ionic liquids with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine liposome

Recent increase and wider use of ionic liquids (ILs) for various applications has drawn attention to their toxicological consequence on human health. The present study explores effects of three different kinds of widely used ILs, such as 1‐methyl‐3‐octylimidazolium chloride, 1‐buytl‐3‐methyl imadazolium tetrafluoroborate and 1‐benzyl‐3‐methyl imidazolium tetrafluoroborate, on liposome properties of 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine (DPPC) by applying curcumin as molecular probe. Fluorescence intensity of curcumin is reported as a novel rotor which is sensitive to viscosity and thus the fluidity of the solvent. It follows a linear relationship of log fluorescence vs viscosity as proposed by Förster–Hoffmann equation. Curcumin binds strongly to liposome. At low concentration, the lipophilic drug curcumin does not appreciably influence the phase transition temperature of DPPC but as concentration reaches high levels significantly depresses the phase transition temperature. ILs diminish membrane fluidity. 1‐methyl‐3‐octylimidazolium chloride disorders membrane properties by lowering the phase transition as is observed for higher concentration of curcumin, but 1‐buytl‐3‐methyl imidazolium tetrafluoroborate and 1‐benzyl‐3‐methyl imidazolium tetrafluoroborate do not modify phase transition temperature perceptibly; rather they broaden the phase transition at low molar concentration ratio. The three different kinds of ILs under study behave similarly at a high IL:DPPC ratio (1:2), while they behave differently at lower ratios (1:10–1:5).     

Effect of increased hydrophobicity on the binding of two model amphiphilic chlorin drugs for photodynamic therapy with blood plasma and its components

The binding of serum albumin and lipoprotein with chlorin p(6) and purpurin 18, two structurally related chlorins, has been studied to understand the role for these proteins as endogenous carriers for these drugs. As a drug carrier a protein may aid in selective delivery of a drug to a tumor region. Binding with serum albumin may result in accumulation of the drug in the stroma of the tumor cell and lead to a reduction of cellular uptake of photosensitizers. However, it is possible that this factor may not be a problem for cellular uptake of chlorin p(6) and purpurin 18 by the tumor tissues, since it binds more efficiently with low-density lipoprotein when it become more lipophilic, indicating that the principal carriers for these molecules are lipoproteins. Since the tumor tissues contain numerous lipoprotein receptors, chlorin p(6) and purpurin 18 could be internalized more efficiently in tumor cells.     

Effect of the lithium cation on the sorption and electrical properties of amphiphilic block copolymers and their composites

The use of lithium cation in composites of block copolymers [polyethylene‐b‐polyethylene oxide (PE‐b‐50%PEO and PE‐b‐80%PEO)] and their derivatives was tested as a modifier of the vapor sorption and impedance of these complexes. The block copolymer PE‐b‐80%PEO was modified by oxidation of its hydroxyl end group to both a carboxylic acid group (PE‐b‐80%PEO)CH₂COOH and its sodium salt (PE‐b‐80%PEO)CH₂COO^? Na⁺ for the purpose of improving its compatibility and performance as a matrix for composites. These modified copolymers were characterized by FTIR, DSC, and mass spectrometry. The sorption of water of these copolymers and their composites with lithium nitrate was also compared, as well as the electrical properties of their composites were measured by electrical impedance spectroscopy. For the composites obtained with PE‐b‐80%PEO and lithium nitrate, it was found that lithium cation plays an important role increasing the sorption rate, which is maximized for the PE‐b‐80%PEO + (21% lithium nitrate) composite. For the copolymers (PE‐b‐80%PEO)CH₂COOH and (PE‐b‐80%PEO)CH₂COO^? Na⁺ and their composites, the highest sorption rate was observed for salt in the following order: COO^? Na⁺ > COOH > OH. The PE‐b‐80%PEO + (21% lithium nitrate) composite behaves as a solid polymeric ionic conductor fitting the Williams–Landel–Ferry equation. However, both (PE‐b‐80% PEO)CH₂COOH and (PE‐b‐80%PEO)CH₂COO^? Na⁺ + (21% lithium nitrate) composites fitted the Variable Range Hopping equation, indicating a conductance trend with temperature governed by a thermally activated with energy of 0.482 and 0.524 eV and not by a relaxation process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1809–1817, 2010     

Small ScCn cyclic clusters: a density functional study of their structure and stability

A theoretical study of the ScCn, ScCn+, and ScCn- (n = 1-10) cyclic clusters has been carried out employing the B3LYP density functional method. Predictions for several molecular properties that could help in their possible experimental characterization, such as equilibrium geometries, electronic structures, dipole moments, and vibrational frequencies, are reported. All ScCn cyclic clusters are predicted to have doublet ground states. For cationic clusters the ground state is alternate between singlets (n-even species) and triplets (n-odd members). In the case of anionic clusters the singlet-triplet separation is relatively small, with the singlets being favored in most cases. In general, even-odd parity effects are also observed for different properties, such as incremental binding energies, ionization energies, and electron affinities. For all neutral, cationic, and anionic clusters it is found that cyclic species are more stable than their open-chain counterparts. Therefore, cyclic structures are the most interesting possible targets for an experimental search of scandium-doped carbon clusters.     

Effect of strain on the photoisomerization and stability of a congested azobenzenophane: a combined experimental and computational study

The stability and trans-cis photoisomerization properties of a macrocycle constituted of two para-aminoazobenzene units connected by two methylene bridges have been investigated by a combination of experimental and computational techniques. Irradiation at 365 nm leads to a photostationary state in which only 50% of the azobenzene units have isomerized, in contrast with the behavior of para-aminoazobenzene, whose photoconversion is larger than 80%. In the case of the macrocycle, a faster cis --> trans thermal back-reaction is observed. To assist the interpretation of the experimental results, molecular mechanics and quantum chemical calculations have been carried out. Of the possible conformers, the most stable trans-trans geometric isomer has been identified along with the more plausible trans-cis and cis-cis isomers. Ground-state energy barriers along the NN torsional coordinates were also computed, along with excitation energies and intensities for the species that can contribute to the photostationary state. The calculations point to a sequential photoisomerization mechanism and support a predominance of the trans-cis photoproduct with minor contributions from the cis-cis species. The thermal and photochemical reactivity of the examined macrocycle is compared to that of previously investigated azobenzenophanes and explained in terms of strain and substituent effects both concurring to favor the thermal cis --> trans back-reaction.     

Synthesis,characterization, density functional theory,X‐ray study,thermal stability,and biological and MOE relevance of metal complexes of griseofulvin

Metal(II) and metal(III) coordination compounds of griseofulvin (GFV) drug were synthesized. The structure of the ligand was determined on the basis of elemental analyses, infrared and ¹H NMR spectroscopies and thermal studies. GFV behaved as a neutral tridentate chelating agent and coordinated to metal ions through three oxygen atoms: two methoxy groups and oxygen atom of furan ring. Metal complexes were characterized by means of elemental analyses and molar conductance, spectral (infrared, electron spin resonance) and thermal studies. All the complexes showed molar conductance behaviour corresponding to an electrolytic nature. All the complexes showed octahedral geometry, except [Zn(GFV)Cl]Cl that showed tetrahedral geometry. Density functional theory (DFT) calculations were employed to understand and estimate the contribution of each interaction in the formation of the assembly using several theoretical models. The computed parameters from DFT calculations for structure optimizations and vibrational frequencies were in good agreement with the experimental data. Newly synthesized metal complexes in addition to GFV were examined against opportunistic pathogens. The biological applications of complexes were studied with two Gram‐positive bacteria (Bacillus subtilis and Staphylococcus aureus) and two Gram‐negative bacteria (Escherichia coli and Neisseria gonorrhoeae) as well as their antifungal activity against Candida albicans. Results suggested that metal complexes were more biologically sensitive than free ligand. The complexes showed a moderate inhibition of MCF7 breast cancer cell line growth. Molecular docking studies further helped in understanding the mode of action of the compounds through their various interactions with the crystal structures of: human serum albumin (PDB: 5FUO), Staphylococcus aureus nucleoside (PDB: 3Q8U), human acetylcholinesterase (PDB: 1B41) and the human DNA–Topo I complex (PDB: 1SC7).     

Activity and stability studies of verbascoside, a novel antioxidant, in dermo-cosmetic and pharmaceutical topical formulations

We here report the results of our investigations carried out on verbascoside, a phenylpropanoid glycoside known for its antioxidant, anti-inflammatory and photoprotective actions. Verbascoside was obtained from Buddleia davidii meristematic cells, obtained in turn using a sustainable biotechnology platform which employs an in vitro plant cell culture technology. Verbascoside was first investigated to assess the behaviour of the active ingredient in solution or in finished preparations, in view of its potential topical use, especially in skin protection. Stability studies were performed by HPLC, and a PCL assay was adopted to determine the radical scavenging activity toward superoxide anion. The high hydrophilic character of verbascoside, suggested in a somewhat limited range of possible applications, leading us to explore its derivatization to obtain the semi-synthetic derivative VPP, an acyl derivative of verbascoside, with an improved range of applications due to its lower hydrophilic profile. Alone, VPP revealed increased antioxidant activity, both as an active ingredient and in dermocosmetic preparations. Stability studies showed a greater stability of VPP in lipophilic vehicles, whereas the parent verbascoside proved more stable in an O/W emulsions. Verbascoside was also stable in suppositories, an interesting pharmaceutical form for possible applications in treatment of inflammation of the intestinal mucosa.