Endohedrally Functionalized Metal-Organic Cage-Cross-Linked Polymer Gels as Modular Heterogeneous Catalysts.

The immobilization of homogeneous catalysts onto supports to improve recyclability while maintaining catalytic efficiency is often a trial-and-error process limited by poor control of the local catalyst environment and few strategies to append catalysts to support materials. Here, we introduce a modular heterogenous catalysis platform that addresses these challenges. Our approach leverages the well-defined interiors of self-assembled Pd12L24 metal-organic cages/polyhedra (MOCs): simple mixing of a catalyst-ligand of choice with a polymeric ligand, spacer ligands, and a Pd salt induces self-assembly of Pd12L24-cross-linked polymer gels featuring endohedrally catalyst-functionalized junctions. Semi-empirical calculations show that catalyst incorporation into the MOC junctions of these materials has minimal affect on the MOC geometry, giving rise to well-defined nanoconfined catalyst domains as confirmed experimentally using several techniques. Given the unique network topology of these freestanding gels, they are mechanically robust regardless of their endohedral catalyst composition, allowing them to be physically manipulated and transferred from one reaction to another to achieve multiple rounds of catalysis. Moreover, by decoupling the catalyst environment (interior of MOC junctions) from the physical properties of the support (the polymer matrix), this strategy enables catalysis in environments where homogeneous catalyst analogues are not viable, as demonstrated for the Au(I)-catalyzed cyclization of 4-pentynoic acid in aqueous media.

Characterization of a fluorescent 1,8-naphthalimide-functionalized PAMAM dendrimer and its Cu(ii) complexes as cytotoxic drugs: EPR and biological studies in myeloid tumor cells.

The activity and interacting ability of a polyamidoamine (PAMAM) dendrimer modified with 4-N-methylpiperazine-1,8-naphthalimide units (termed D) and complexed by Cu(ii) ions, towards healthy and cancer cells were studied. Comparative electron paramagnetic resonance (EPR) studies of the Cu(ii)-D complex are presented: coordination mode, chemical structure, flexibility and stability of these complexes, in the absence and presence of myeloid cancer cells and peripheral blood mononuclear cells (PBMC). The interactions of Cu(ii) ions in the biological media at different equilibrium times were studied, highlighting different stability and interacting conditions with the cells. Furthermore, flow cytometry and confocal analysis, trace the peculiar properties of the dendrimers in PBMC and U937 cells. Indeed, a new probe (Fly) was used as a potential fluorescent tool for biological imaging of Cu(ii). The study highlights that dendrimer and, mainly, the Cu(ii) metallodendrimer are cytotoxic agents for the cells, specifically for U937 tumor cells, inducing mitochondrial dysfunction, ROS increase and lysosome involvement. The metallodendrimer shows antitumor selectivity, fewer affecting healthy PBMC, inducing a massive apoptotic cell death on U937 cells, in line with the high stability of this complex, as verified by EPR studies. The results underline the potentiality of this metallodendrimer to be used as anticancer drug.

Order vs. Disorder: Cholesterol and Omega-3 Phospholipids Determine Biomembrane Organization.

Lipid structural diversity strongly affects biomembrane chemico-physical and structural properties in addition to membrane-associated events. At high concentrations, cholesterol increases membrane order and rigidity, while polyunsaturated lipids are reported to increase disorder and flexibility. How these different tendencies balance in composite bilayers is still controversial. In this study, electron paramagnetic resonance spectroscopy, small angle neutron scattering, and neutron reflectivity were used to investigate the structural properties of cholesterol-containing lipid bilayers in the fluid state with increasing amounts of polyunsaturated omega-3 lipids. Either the hybrid 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine or the symmetric 1,2-docosahexaenoyl-sn-glycero-3-phosphocholine were added to the mixture of the naturally abundant 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine and cholesterol. Our results indicate that the hybrid and the symmetric omega-3 phospholipids affect the microscopic organization of lipid bilayers differently. Cholesterol does not segregate from polyunsaturated phospholipids and, through interactions with them, is able to suppress the formation of non-lamellar structures induced by the symmetric polyunsaturated lipid. However, this order/disorder balance leads to a bilayer whose structural organization cannot be ascribed to either a liquid ordered or to a canonical liquid disordered phase, in that it displays a very loose packing of the intermediate segments of lipid chains.

Fine-Tuning the Interaction and Therapeutic Effect of Cu(II) Carbosilane Metallodendrimers in Cancer Cells: An In Vitro Electron Paramagnetic Resonance Study.

Copper(II) carbosilane metallodendrimers are promising nanosized anticancer metallodrugs. The precise control on their design enables an accurate structure-to-activity study. We hypothesized that different structural features, such as the dendrimer generation and metal counterion, modulate the interaction with tumor cells, and subsequently, the effectivity and selectivity of the therapy. A computer-aided analysis of the electron paramagnetic resonance (EPR) spectra allowed us to obtain dynamical and structural details on the interactions over time between the dendrimers and the cells, the myeloid U937 tumor cells and peripheral blood mononuclear cells (PBMC). The intracellular fate of the metallodendrimers was studied through a complete in vitro evaluation, including cytotoxicity, cytostaticity, and sublethal effects regarding mitochondria function, lysosomal compartments, and autophagic organelle involvement. EPR results confirmed a higher membrane stabilization for chloride dendrimers and low generation complexes, which ultimately influence the metallodrug uptake and intracellular fate. The in vitro evaluation revealed that Cu(II) metallodendrimers are cytostatic and moderate cytotoxic agents for U937 tumor cells, inducing death processes through the mitochondria-lysosome axis as well as autophagic vacuole formation, while barely affecting healthy monocytes. The study provided valuable insight into the mechanism of action of these nanosized metallodrugs and relevant structural parameters affecting the activity.

DOTA Glycodendrimers as Cu(II) Complexing Agents and Their Dynamic Interaction Characteristics toward Liposomes.

Copper (Cu)(II) ions, mainly an excess amount, play a negative role in the course of several diseases, like cancers, neurodegenerative diseases, and the so-called Wilson disease. On the contrary, Cu(II) ions are also capable of improving anticancer drug efficiency. For this reason, it is of great interest to study the interacting ability of Cu(II)-nanodrug and Cu(II)-nanocarrier complexes with cell membranes for their potential use as nanotherapeutics. In this study, the complex interaction between 1,4,7,10-tetraazacyclododecan-N,N',N'',N'''-tetraacetic acid (DOTA)-functionalized poly(propyleneimine) (PPI) glycodendrimers and Cu(II) ions and/or neutral and anionic lipid membrane models using different liposomes is described. These interactions were investigated via dynamic light scattering (DLS), ζ-potential (ZP), electron paramagnetic resonance (EPR), fluorescence anisotropy, and cryogenic transmission electron microscopy (cryo-TEM). Structural and dynamic information about the PPI glycodendrimer and its Cu(II) complexes toward liposomes was obtained via EPR. At the binding site Cu-N2O2 coordination prevails, while at the external interface, this coordination partially weakens due to competitive dendrimer-liposome interactions, with only small liposome structural perturbation. Fluorescence anisotropy was used to evaluate the membrane fluidity of both the hydrophobic and hydrophilic parts of the lipid bilayer, while DLS and ZP allowed us to determine the distribution profile of the nanoparticle (PPI glycodendrimer and liposomes) size and surface charge, respectively. From this multitechnique approach, it is deduced that DOTA-PPI glycodendrimers selectively extract Cu(II) ions from the bioenvironment, while these complexes interact with the liposome surface, preferentially with even more negatively charged liposomes. However, these complexes are not able to cross the cell membrane model and poorly perturb the membrane structure, showing their potential for biomedical use.

Not just a fluidifying effect: omega-3 phospholipids induce formation of non-lamellar structures in biomembranes.

Polyunsaturated omega-3 fatty acid docosahexaenoic acid (DHA) is found in very high concentrations in a few peculiar tissues, suggesting that it must have a specialized role. DHA was proposed to affect the function of the cell membrane and related proteins through an indirect mechanism of action, based on the DHA-phospholipid effects on the lipid bilayer structure. In this respect, most studies have focused on its influence on lipid-rafts, somehow neglecting the analysis of effects on liquid disordered phases that constitute most of the cell membranes, by reporting in these cases only a general fluidifying effect. In this study, by combining neutron reflectivity, cryo-transmission electron microscopy, small angle neutron scattering, dynamic light scattering and electron paramagnetic resonance spectroscopy, we characterize liquid disordered bilayers formed by the naturally abundant 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine and different contents of a di-DHA glycero-phosphocholine, 22:6-22:6PC, from both a molecular/microscopic and supramolecular/mesoscopic viewpoint. We show that, below a threshold concentration of about 40% molar percent, incorporation of 22:6-22:6PC in the membrane increases the lipid dynamics slightly but sufficiently to promote the membrane deformation and increase of multilamellarity. Notably, beyond this threshold, 22:6-22:6PC disfavours the formation of lamellar phases, leading to a phase separation consisting mostly of small spherical particles that coexist with a minority portion of a lipid blob with water-filled cavities. Concurrently, from a molecular viewpoint, the polyunsaturated acyl chains tend to fold and expose the termini to the aqueous medium. We propose that this peculiar tendency is a key feature of the DHA-phospholipids making them able to modulate the local morphology of biomembranes.

In Depth Analysis of Photovoltaic Performance of Chlorophyll Derivative-Based "All Solid-State" Dye-Sensitized Solar Cells.

Chlorophyll a derivatives were integrated in "all solid-state" dye sensitized solar cells (DSSCs) with a mesoporous TiO2 electrode and 2',2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene as the hole-transport material. Despite modest power conversion efficiencies (PCEs) between 0.26% and 0.55% achieved for these chlorin dyes, a systematic investigation was carried out in order to elucidate their main limitations. To provide a comprehensive understanding of the parameters (structure, nature of the anchoring group, adsorption …) and their relationship with the PCEs, density functional theory (DFT) calculations, optical and photovoltaic studies and electron paramagnetic resonance analysis exploiting the 4-carboxy-TEMPO spin probe were combined. The recombination kinetics, the frontier molecular orbitals of these DSSCs and the adsorption efficiency onto the TiO2 surface were found to be the key parameters that govern their photovoltaic response.

Structural Characterization of Reconstituted Bioactive-Loaded Nanodomains after Embedding in Films Using Electron Paramagnetic Resonance and Self-Diffusion Nuclear Magnetic Resonance Techniques.

Pharmaceutical applications of microemulsions (MEs) as drug delivery vehicles are recently gaining scientific and practical interests. Most MEs are able to solubilize bioactive molecules, but, at present, they cannot guarantee either controlled release of the drugs or significant advantage in the bioavailability of the bioactives. This study proposes to incorporate the modified ME structures, or nanodomains, into a natural polymeric film, to be used as a stable and capacious reservoir of drug-loaded nanodomains. These nanodomain-loaded films may release the nanodroplets along with the drug molecules in a slow and controlled way. Gellan gum, an anionic polysaccharide, was used in aqueous solution as the film former, and curcumin, hydrophobic polyphenol, served as the guest molecule in the loaded systems. Films were prepared by using empty and curcumin-loaded MEs. It is imperative to verify the persistence of the ME structure upon the dissolution of the film mimicking its behavior when in contact with a human physiological aqueous environment via reaching the cell membranes. For this purpose, the films were dissolved, and the reconstituted ME structure was compared with the ME structure before film formation. Characterization of these structures, before and after dissolution, was achieved using electron paramagnetic resonance (EPR) and self-diffusion nuclear magnetic resonance (SD-NMR) techniques. Specific spin probes were inserted in the system, and a computer-aided analysis of the EPR spectra was performed to provide information on nanodomain microstructure assemblies. In addition, the SD-NMR profile of each component was analyzed to extract information on the diffusivity of the ME components before film formation and after ME reconstitution. The EPR and SD-NMR results were in good agreement to each other. The most important finding was that, after film dissolution, the ME nanodomains were reversibly and spontaneously reformed. It was also found that the film did not perturb the ME-nanodomain structure embedded in it. The film remained transparent and the bioactive curcumin was easily solubilized into the ME-droplet/water interface even after film dissolution. The combined techniques confirmed that the film constituted by bioactive-loaded MEs can serve as novel drug delivery vehicles.

Interactions of Nitroxide-Conjugated and Non-Conjugated Glycodendrimers with Normal and Cancer Cells and Biocompatibility Studies.

Poly(propyleneimine) glycodendrimers fully modified with maltose units were administered to different cancer cell lines and their effect on cell viability was evaluated by using MTS assay and flow cytometry. The mechanism of dendrimer-cell interactions was investigated by the electron paramagnetic resonance (EPR) technique by using a new nitroxide-conjugated glycodendrimer. The nitroxide groups did not modify both the biological properties (cell viability and apoptosis degree) of the dendrimers in the presence of the cells and the dendrimer-cell interactions. Since this class of dendrimers is already known to be biocompatible for human healthy cells, noncancer cells such as human peripheral blood mononuclear cells (PBMCs) and macrophages were also treated with the glycodendrimer, and EPR spectra of the nitroxide-conjugated glycodendrimer were compared for cancer and noncancer cells. It was found that this dendrimer selectively affects the cell viability of tumor cells, while, surprisingly, PBMC proliferation is induced. Moreover, H-bond-active glycodendrimer-cell interactions were different for the different cancer cell lines and noncancer cells. The nitroxide-conjugated glycodendrimer was able to interact with the cell membrane and eventually cross it, getting in contact with cytosol antioxidants. This study helps to clarify the potential anticancer effect of this class of dendrimers opening to future applications of these macromolecules as new antitumor agents.

Self-Assembled Ligands Targeting TLR7: A Molecular Level Investigation.

Toll-like receptors (TLRs) are pattern recognition transmembrane proteins that play an important role in innate immunity. In particular, TLR7 plays a role in detecting nucleic acids derived from viruses and bacteria. The huge number of pathologies in which TLR7 is involved has led to an increasing interest in developing new compounds targeting this protein. Several conjugation strategies were proposed for TLR7 agonists to increase the potency while maintaining a low toxicity. In this work, we focus the attention on two promising classes of TLR7 compounds derived from the same pharmacophore conjugated with phospholipid and polyethylene glycol (PEG). A multidisciplinary investigation has been carried out by molecular dynamics (MD), dynamic light scattering (DLS), electron paramagnetic resonance (EPR), and cytotoxicity assessment. DLS and MD indicated how only the phospholipid conjugation provides the compound abilities to self-assemble in an orderly fashion with a maximal pharmacophore exposition to the solvent. Further EPR and cytotoxicity experiments highlighted that phospholipid compounds organize in stable aggregates and well interact with TLR7, whereas PEG conjugation was characterized by poorly stable aggregates at the cells surface. The methodological framework proposed in this study may be used to investigate, at a molecular level, the interactions generally occurring between aggregated ligands, to be used as drugs, and protein receptors.

Electron paramagnetic resonance and transmission electron microscopy study of the interactions between asbestiform zeolite fibers and model membranes.

Different asbestiform zeolite fibers of the erionite (termed GF1 and MD8, demonstrated carcinogenic) and offretite (termed BV12, suspected carcinogenic) families were investigated by analyzing the electron paramagnetic resonance (EPR) spectra of selected surfactant spin probes and transmission electron microscopy (TEM) images in the presence of model membranes-cetyltrimethylammonium (CTAB) micelles, egg-lecithin liposomes, and dimyristoylphosphatidylcholine (DMPC) liposomes. This was undertaken to obtain information on interactions occurring at a molecular level between fibers and membranes which correlate with entrance of fibers into the membrane model or location of the fibers at the external or internal membrane interfaces. For CTAB micelles, all fibers were able to enter the micelles, but the hair-like structure and chemical surface characteristics of GF1 modified the micelle structure toward a bilayer-like organization, while MD8 and BV12, being shorter fibers and with a high density of surface interacting groups, partially destroyed the micelles. For liposomes, GF1 fibers partially penetrated the core solution, but DMPC liposomes showed increasing rigidity and organization of the bilayer. Conversely, for MD8 and BV12, the fibers did not cross the membrane demonstrating a smaller membrane structure perturbation. Scolecite fibers (termed SC1), used for comparison, presented poor interactions with the model membranes. The carcinogenicity of the zeolites, as postulated in the series SC1

Bifunctional chelating agents based on ionic carbosilane dendrons with DO3A at the focal point and their complexation behavior with copper(II).

A synthetic protocol has been designed to incorporate the DO3A ligand to the focal point of cationic or anionic carbosilane dendrons, affording a set of bifunctional chelating agents (BFCAs) useful for potential biomedical applications. The complexation behavior study of ionic BFCAs has been accomplished by UV-vis and electron paramagnetic resonance spectroscopy as well as potentiometric titrations. The presence of the dendron branches modifies the complexation capacity of the macrocyclic ring with respect to that of the 1,4,7,10-tetraazacyclodocecane-N,N',N″,N‴-tetraacetic acid (DOTA) ligand. Also, a different behavior has been observed in the carboxylate-terminated dendrons against analogous sulfonate- or amine-terminated dendrons in the contribution of the branches and peripheral groups to the coordination modes. The presence or not of Cu-S2O2 coordination sites and the generation can be important factors to take into account for considering a particular biomedical application.

Characterization of the TiO2/dye/electrolyte interfaces in dye-sensitized solar cells by means of a titania-binding nitroxide.

Dye-sensitized solar cells (DSSCs) have been characterized in several literature examples by using relatively complex methods and/or modified DSSC conditions with respect to the usual working ones. In this study, we propose a method for the investigation of the interfaces TiO2/dye/electrolyte in a DSSC at its usual working conditions. This method implies the use of a computer-aided analysis of the electron paramagnetic resonance (EPR) spectra of the spin probe 4-carboxy-2,2,6,6-tetramethylpiperidine 1-oxyl (4-carboxy-TEMPO, indicated as 4-cT). This probe well-mimics the dyes in their interactions with TiO2 surface, but does not perturb dye adsorption onto TiO2 surface, as verified by UV-vis measurements. First, we investigated the interacting ability toward 4-cT of commercially available TiO2 used for assembling the DSSC. It was found that interactions are modulated by the different distribution of interacting sites at the solid surface and powder aggregation. Further, experiments on 4-cT were carried out in the presence of a series of other molecules coded as N3, N719, and D149, which are commonly used as dyes in DSSCs. Then, the effect of solutions added to the electrodes was investigated. On the basis of the interactions occurring at the TiO2/dye/electrolyte interfaces, we selected the ingredients of the DSSCs. Electrical and EPR characterizations of these DSSCs miniaturized to enter the EPR cavity, together with time-dependent laser-light on-off experiments, were carried out, which demonstrated the ability of the EPR analysis to monitor the types and strengths of the interactions occurring at the cell's different interfaces. This method using the standard continuous wave EPR technique at room temperature may be profitably used to characterize the quality and performances of a DSSC.

EPR and rheological study of hybrid interfaces in gold-clay-epoxy nanocomposites.

With the aim to obtain new materials with special properties to be used in various industrial and biomedical applications, ternary "gold-clay-epoxy" nanocomposites and their nanodispersions were prepared using clay decorated with gold nanoparticles (AuNPs), at different gold contents. Nanocomposites structure was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Rheology and electron paramagnetic resonance (EPR) techniques were used in order to evaluate the molecular dynamics in the nanodispersions, as well as dynamics at interfaces in the nanocomposites. The percolation threshold (i.e., the filler content related to the formation of long-range connectivity of particles in the dispersed media) of the gold nanoparticles was determined to be ϕp = 0.6 wt % at a fixed clay content of 3 wt %. The flow activation energy and the relaxation time spectrum illustrated the presence of interfacial interactions in the ternary nanodispersions around and above the percolation threshold of AuNPs; these interfacial interactions suppressed the global molecular dynamics. It was found that below ϕp the free epoxy polymer chains ratio dominated over the chains attracted on the gold surfaces; thus, the rheological behavior was not significantly changed by the presence of AuNPs. While, around and above ϕp, the amount of the bonded epoxy polymer chains on the gold surface was much higher than that of the free chains; thus, a substantial increase in the flow activation energy and shift in the spectra to higher relaxation times appeared. The EPR signals of the nanocomposites depended on the gold nanoparticle contents and the preparation procedure thus providing a fingerprint of the different nanostructures. The EPR results from spin probes indicated that the main effect of the gold nanoparticles above ϕp, was to form a more homogeneous, viscous and polar clay-epoxy mixture at the nanoparticle surface. The knowledge obtained from this study is applicable to understand the role of interfaces in ternary nanocomposites with different combinations of nanofillers.

Copper(II) binding to flexible triethanolamine-core PAMAM dendrimers: a combined experimental/in silico approach.

The structure of copper(II) complexes formed with triethanolamine (TEA) core poly(amidoamine) (PAMAM) dendrimers from generation 0 (G0) to 4 (G4) were investigated by the electron paramagnetic resonance (EPR) technique and molecular simulations. Different square planar coordination modes were detected as a function of copper(II) concentration, whose dynamic evolution relates to the high structural flexibility peculiar to this dendrimer family. Modulated by generation and solvation effects, copper(II) complexation begins at the dendrimer core and progresses to the dendrimer periphery. Differently from the ethylenediamine (EDA) core PAMAM dendrimers, the copper complexes involving the TEA core showed high mobility and saturation of the internal sites above the 1 : 1 molar ratio between the dendrimers and the ions. Therefore, by combining EPR and molecular simulations for the first time, ultimately we obtained unique information on structure, dynamics and copper interacting ability of these dendrimers which could be successfully exploited in biomedical applications.

Effect of hydrogenated cardanol on the structure of model membranes studied by EPR and NMR.

Hydrogenated cardanol (HC) is known to act as an antiobesity, promising antioxidant, and eco-friendly brominating agent. In this respect, it is important to find the way to transport and protect HC into the body; a micellar structure works as the simplest membrane model and may be considered a suitable biocarrier for HC. Therefore, it is useful to analyze the impact of HC in the micellar structure and properties. This study reports a computer aided electron paramagnetic resonance (EPR) and (1)H NMR investigation of structural variations of cetyltrimetylammonium bromide (CTAB) micelles upon insertion of HC at different concentrations and pH variations. Surfactant spin probes inserted in the micelles allowed us to get information on the structure and dynamics of the micelles and the interactions between HC and CTAB. The formation of highly packed HC-CTAB mixed micelles were favored by the occurrence of both hydrophobic (chain-chain) and hydrophilic (between the polar and charged lipid heads) interactions. These interactions were enhanced by neutralization of the acidic HC heads. Different HC localizations into the micelles and micellar structures were identified by changing HC/CTAB relative concentrations and pH. The increase in HC concentration generated mixed micelles characterized by an increased surfactant packing. These results suggested a rod-like shape of the mixed micelles. The increase in pH promoted the insertion of deprotonated HC into less packed micelles, favored by the electrostatic head-head interactions between CTAB and deprotonated-HC surfactants.

Amphiphilic Dendritic Hydrogels with Carbosilane Nanodomains: Preparation and Characterization as Drug Delivery Systems.

Carbosilane dendrimers are hyperbranched lipophilic scaffolds widely explored in biomedical applications. This work exploits, for the first time, the ability of these scaffolds to generate functional hydrogels with amphiphilic properties. The monodispersity and multivalency enable a precise synthetic control of the network, while the lipophilicity improves the compatibility with poorly soluble cargo. The first family of cleavable carbosilane dendrimers was designed for this purpose, overcoming one of the main drawbacks of these type of dendrimers. Biodegradable dendritic low-swelling hydrogels with aromatic nanodomains were easily prepared using the highly efficient click thiol-ene chemistry. Our studies through electron-paramagnetic resonance, molecular dynamics simulations, and experimental assays confirmed the impact of the carbosilane dendritic nanodomains in both the encapsulation and the release pattern of model drugs such as ibuprofen and curcumin. Curcumin-loaded hydrogels were further tested in in vitro assays against advanced prostate cancer cells. The dendritic hydrogels not only enabled drugs encapsulation; as proof of concept, ibuprofen was efficiently attached via fluoride-promoted esterification and was enzymatically cleaved, achieving a controlled release over time.

Spin probe analysis of microtubules structure and formation.

Microtubules (MTs) control cell replication, material transport and motion in eukaryotic cells, but MT role in several pathologies is still unknown. These functions are related to the MT physico-chemical properties and MT formation mode starting from tubulin molecules. This study describes a new method, based on the computer aided analysis of the electron paramagnetic resonance (EPR) spectra of selected spin probes to obtain structural and dynamical information on tubulins and MTs and the kinetics of MTs formation promoted by guanosine-5'-triphosphate (GTP). It was found that tubulin and MTs avoid radical quenching caused by ethylene glycol tetraacetic acid (EGTA). MT formation showed different kinetics as a function of tubulin concentration. At 5 mg/mL of tubulin, MTs were formed in 8 min. These results are also useful for getting information on MT-drug interactions.

Interactions of Functionalized PAMAM Dendrimers with Model Cell Membranes Studied via Spin-Labeling Technique.

Polyamidoamine (PAMAM) dendrimers are exploited as drug carriers in various biomedical research fields, especially cancer therapy. The present study analyzes the interactions occurring between differently functionalized PAMAM dendrimers, namely, amine, acetamide, and 3-methoxy-carbonyl-5-pyrrolidonyl ("pyrrolidone"), and model membranes, namely, sodium dodecyl sulfate (SDS), sodium hexadecylsulfate (SHS) micelles, and egg-lecithin liposomes. For this purpose, the dendrimers were spin-labeled with the 3-carbamoyl-PROXYL radical. 1H-NMR spectra allowed the verification not only that labeling was successful but also that acetamide and (even more so) pyrrolidone functions shield the proton signals from the influence of the neighboring nitroxide groups. The computer-aided analysis of the electron paramagnetic resonance (EPR) spectra showed that the dendrimers with the acetamide function largely (60%) entered the SDS-micelles interface, while the amino-dendrimer electrostatically interacted with both the SDS and SHS surface forming dendrimer aggregates in solution. The pyrrolidone-dendrimers showed an intermediate behavior between those with the amino and acetamide functions. The acetamide- and pyrrolidone-dendrimers weakly interacted with the lecithin liposome surface, with a synergy between hydrophilic and hydrophobic interactions. Conversely, liposomes/amino-dendrimers interactions were quite strong and led to dendrimer aggregation at the liposome surface in solution. This information showed that acetamide- and pyrrolidone-dendrimers may be used as good alternatives to amino-dendrimers for drug delivery.

Synthesis and biological and physico-chemical characterization of glycodendrimers and oligopeptides for the treatment of systemic lupus erythematosus.

Anti-(ds)-DNA antibodies are the serological hallmark of Systemic Lupus Erythematosus (SLE). They assemble in the bloodstream with (ds)-DNA, forming immunocomplexes, which spread all over the body causing, among the other symptoms, lupic glomerulonephritis. Pathological manifestations of the disease may be reduced by destabilizing or inhibiting the formation of the immunocomplexes. In this respect, glycodendrimers showed peculiar interacting abilities towards this kind of biomolecule. Various generations of open-shell maltose-decorated poly(amidoamine) (PAMAM) and poly(propyleneimine) (PPI) dendrimers and two oligopeptides with different polyethylene glycol units were synthesized and characterized, and then tested for their anti-SLE activity. The activity of glycodendrimers and oligopeptides was evaluated in human plasma from patients with SLE, compared to healthy plasma, by means of an enzyme-linked immunosorbent assay (ELISA), and electron paramagnetic resonance (EPR) characterization using spin-label and spin-probe techniques. Different strategies for the immunocomplex formation were tested. The results show that both kinds of glycodendrimers and oligopeptides inhibited the formation of immunocomplexes. Also, a partial breakdown of preformed immunocomplexes was observed. Both ELISA and EPR analyses indicated a better activity of glycodendrimers compared to oligopeptides, the 3rd generation PPI dendrimer being the most promising against SLE. This study highlights the possibility to develop a new class of dendritic therapeutics for the treatment of Lupus in pre-clinical studies.