Layer by layer assembly of core-corona structured solid lipid nanoparticles with ß-cyclodextrin polymers.

This study aims to design and characterize the layer-by-layer assembly of core-corona nanoarchitecture for novel surface-modified solid lipid nanoparticles. Oppositely charged ß-cyclodextrin polymers were used to build corona structure onto lipid core, and the particle size, polydispersity index, and zeta potential of SLN with polymer layers were evaluated. Morphology of surface-modified SLN was identified using TEM. The effect of polymer coating on drug release pattern was investigated by in-vitro release studies. The biocompatibility of the novel SLN systems was assessed on various healty cell lines using in vitro cytotoxicity assay. The presence of the oppositely charged polymer layers was found to be effective on alteration of zeta potential from negative to positive values and an increased surface charge density was achieved in comparison to core SLN. The results also revealed that the drug release is mainly controlled by diffusion and ß-cyclodextrin polymers could enhance the slow/controlled release of drug. Cytotoxicity assay results suggested that the novel, hierarchical core-corona structured SLNs don't have cytotoxic effects on healthy cells and can be safely used as drug carriers. Overall, the layer-by-layer assembly of ß-cyclodextrin polymers is promising for designing surface-modified nanoarchitectures of lipid nanoparticles that may be applied via many administration routes.

4-Sulfonatocalixarene-induced nanoparticle formation of methylimidazolium-conjugated dextrans: Utilization for drug encapsulation.

Methylimidazolium side groups were grafted via ether linkage to dextran and the self-assembly of these polymers with 4-sulfonato-calix[n]arenes (SCXn) was studied in aqueous solutions. Dynamic light scattering and zeta potential measurements revealed the mixing ratio ranges of the constituents where stable nanoparticles could be created. The macrocycle size of SCXn and the molecular mass of the polymer barely affected the nanoparticle diameter, but the lowering of the imidazolium degree of substitution substantially diminished the stability of the associates. The pH change from neutral to acidic also unfavourably influenced the self-organization owing mainly to the decrease of the SCXn charge. Cryogenic transmission electron microscopy images proved the spherical morphology of the nanoproducts in which the stoichiometry of the constituents was always close to the one corresponding to charge compensation. The flexible and positively charged dextran-chains are compacted by the polyanionic SCXn. Coralyne, a pharmacologically important alkaloid was efficiently embedded by self-assembly in the produced nanoparticles reaching 99% association efficiency.

Self-assembled nanoparticles based on cyclodextrin-modified pullulan: Synthesis, and structural characterization using SAXS.

Synthesis of novel host-guest functionalized polymers is presented along with structural characterization using small-angle X-ray scattering (SAXS) of the resulting nanoparticles. Mono-6-deoxy-mono-6-azidoßCD (N3ßCD) was grafted onto alkyne-functionalized pullulan via the "click" reaction copper(I)-catalyzed azide alkyne cycloaddition (CuAAC) and an adamantane-modified dextran was prepared via the same strategy. Characterization of the polymers was carried out using nuclear magnetic resonance (NMR) spectroscopy, gel filtration chromatography (GFC), isothermal titration calorimetry (ITC) and SAXS. Nanoparticles were created via host-guest interactions between the well-defined ßCD-pullulans and adamantane-modified dextran. Characterization was carried out using dynamic light scattering (DLS) and SAXS, which revealed spherical particles in the sub-100 nm range. The studies shed light on the importance of molecular structure and host-guest ratio on crucial properties such as particle size, size distribution, porosity and stability towards aggregation.

Substituent Effects on the Inclusion of 1-Alkyl-6-alkoxy-quinolinium in 4-Sulfonatocalix[n]arenes.

The effect of the chain length of the alkyl and alkoxy substituents on the binding characteristics of 1-alkyl-6-alkoxy-quinolinium cations was studied using 4-sulfonatocalix[4]arene (SCX4) and 4-sulfonatocalix[6]arene (SCX6) in neutral aqueous solutions at 298 K. Isothermal calorimetric titrations showed enthalpy-controlled inclusion with 1:1 stoichiometry. The equilibrium constants of complexation were always larger for the confinement in SCX4 than in its SCX6 homologue because the better matching between the host and guest sizes allowed more exothermic interaction. The binding affinity diminished with the lengthening of the aliphatic chain of the guests in the case of the association with SCX4, but insignificant change was found for SCX6 complexes. The most substantial change in the enthalpic and entropic contributions to the driving force of complex production occurred when the alkyl chain was linked to the heterocyclic nitrogen and the number of its carbon atoms varied between 1 and 4. 1H NMR spectra evidenced that in SCX6, the 1-alkyl-6-alkoxy-quinolinium cations could be included within the macrocycle cavity. In the case of SCX4, the quinolinium ring is always inside the host, but the alkyl chain is included within SCX4 only for a short chain length (n up to 4). In contrast, the alkoxy chain displays a very weak interaction with the cavity irrespective of the length. Because of the outward orientation from the host, the lengthening of the alkoxy substituent of the quinolinium moiety barely influenced the thermodynamics of inclusion in SCX4. Distinct linear enthalpy-entropy correlations were found for the encapsulation in SCX4 and SCX6.

Effect of Headgroup Variation on the Self-Assembly of Cationic Surfactants with Sulfonatocalix[6]arene.

The effect of headgroup variation on the association of supramolecular amphiphiles composed of 4-sulfonatocalix[6]arene (SCX6) and cationic surfactant possessing tetradecyl substituent was studied in aqueous solutions at pH 7. When the surfactant contained hydrophilic trimethylammonium, pyridinium, or 1-methylimidazolium headgroup, highly reversible temperature-responsive nanoparticle-supramolecular micelle transformation could be attained at appropriately chosen component mixing ratios and NaCl concentrations. In these cases, the substantial negative molar heat capacity change (ΔCp) rendered nanoparticle formation strongly endothermic at low temperature, whereas the assembly to supramolecular micelle was always accompanied by enthalpy gain. The ΔCp values became less negative when the charge density and the hydrophilic character of the surfactant headgroup diminished. The association of the more hydrophobic 6-methoxyquinolinium and quinolinium surfactants with SCX6 did not lead to supramolecular micelle formation because the self-assembly into nanoparticles was highly exothermic.

Host-guest interaction and structural ordering in polymeric nanoassemblies: Influence of molecular design.

Host-guest nanoassemblies made from spontaneous self-association of host and guest polymers in aqueous solutions have been studied. The specific motivation behind this work was to clarify the impact of the molecular design of the polymers on the interactions between them and on the inner structure of the resulting nanoassemblies. The polymers were composed of a dextran backbone, functionalized with either pendant ß-cyclodextrin (CD) or adamantyl (Ada). Those groups were connected to the backbone either directly or with hydrophilic polyethylene glycol (PEG) spacers. To study the impact of those spacers we have proposed a synthetic pathway to new guest polymers. The latter relied on the use of thiol-substituted dextrans as a scaffold, which is subsequently transformed into PEG-Ada grafted guest polymers via nucleophile-mediated thiol-click reaction. Surface plasmon resonance (SPR) studies evidenced strong mutual affinities between the host and guest polymers and showed that the stoichiometry was close to the ideal one (CD/Ada = 1/1) when PEG spacers were introduced. The structure of the nanoassemblies was studied by a combination of dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS). The nature of the individual host or guest polymers has a strong impact on the size and internal structure of the resulting nanoassemblies. The presence of PEG spacers in the polymers led to smaller and less compact nanoassemblies, as evidenced by their large correlation length values (4-20nm compared to 2nm without PEG spacers). At the same time, all types of nanoassemblies appear to have radial density distribution with denser cores and pending polymer chains at the periphery. This study, centered on the influence of the molecular design on the host-guest interactions and structural ordering in polymeric nanoassemblies, will help to tailor host-guest nanoassemblies with attractive drug delivery profiles.

Effect of Macrocycle Size on the Self-Assembly of Methylimidazolium Surfactant with Sulfonatocalix[n]arenes.

The effect of macrocycle size on the association of supramolecular amphiphiles composed of 4-sulfonatocalix[n]arene and 1-methyl-3-tetradecylimidazolium (C14mim+) was studied in aqueous solutions at pH 7. When the cavitand contained four sulfonatophenol units (SCX4), formation of spherical nanoparticles (NPs) was observed. By contrast, both supramolecular micelle (SM) and NP formation could be attained in the presence of NaCl when the larger, more flexible 4-sulfonatocalix[8]arene (SCX8) served as the host compound. The SCX8-promoted self-assembly into the SM was enthalpically more favorable than the NP production, but the molar heat capacity changes in the two processes barely differed. An addition of 50 mM NaCl significantly increased the enthalpy of C14mim+-SCX8 NP formation, thereby making the self-organization into the SM more favorable. The transformation of SM into NP at high temperatures was due to the substantial entropic contribution to the driving force behind the NP formation. The critical micelle concentration (cmc) and the local polarity in the headgroup domain were considerably lower for the SM compared with those of the conventional C14mim+Br- micelle.

Bifunctionalized dextrans for surface PEGylation via multivalent host-guest interactions.

The main goal of this work was to develop a supramolecular chemistry strategy to decorate interfaces with polyethylene glycol (PEG) grafts. A series of novel bifunctionalized dextrans, bearing 40-60 PEG pending chains and 12-24 hydrophobic adamantyl groups, have been prepared by copper(I)-catalyzed azide-alkyne cycloaddition. Their binding properties toward native ßCD and ßCD polymers were characterized both in solution and at interface using isothermal titration microcalorimetry and surface plasmon resonance. The polymers were found to form stable layers onto neutral and positively charged ßCD-polymer films pre-adsorbed on gold surfaces, due to multivalent interpolymer host-guest interactions. The thickness and stability of the layers could be tuned by varying the ratio between the degrees of substitution by PEG and adamantyl groups.

Cyclodextrin/dextran based hydrogels prepared by cross-linking with sodium trimetaphosphate.

Novel ßCD-based hydrogels have been synthesized using sodium trimetaphosphate (STMP) as non-toxic reagent. Straightforward mixing of ßCD with dextran and STMP in basic aqueous media led to hydrogels incorporating dextran chains, phosphate groups and ßCD units. The hydrogels have been characterized by swelling measurements, XPS and (31)P NMR. The swelling ratio was correlated to the content in phosphated groups, which give a polyelectrolyte character to these hydrogels. The significant rise of the swelling ratio with the ßCD content increase has been attributed to a decrease of the number of phosphate-based crosslinks, the ßCD units playing the role of dangling ends in the tridimensional network. Their loading capacity and their release properties have been investigated for methylene blue and benzophenone in order to demonstrate their potentiality for drug delivery. Through different interaction mechanisms, electrostatic and inclusion complex interactions, these compounds are loaded with different efficiencies. The release involves deswelling, diffusion mechanisms and partition equilibrium.

Reversible Nanoparticle-Micelle Transformation of Ionic Liquid-Sulfonatocalix[6]arene Aggregates.

The effect of temperature and NaCl concentration variations on the self-assembly of 1-methyl-3-tetradecylimidazolium (C14mim(+)) and 4-sulfonatocalix[6]arene (SCX6) was studied by dynamic light scattering and isothermal calorimetric methods at pH 7. Inclusion complex formation promoted the self-assembly to spherical nanoparticles (NP), which transformed to supramolecular micelles (SM) in the presence of NaCl. Highly reversible, temperature-responsive behavior was observed, and the conditions of the NP-SM transition could be tuned by the alteration of C14mim(+):SCX6 mixing ratio and NaCl concentration. The association to SM was always exothermic with enthalpy independent of the amount of NaCl. In contrast, NPs were produced in endothermic process at low temperature, and the enthalpy change became less favorable upon increase in NaCl concentration. The NP formation was accompanied by negative molar heat capacity change, which further diminished when NaCl concentration was raised.

Formation of nanoparticles by cooperative inclusion between (S)-camptothecin-modified dextrans and ß-cyclodextrin polymers.

Novel (S)-camptothecin-dextran polymers were obtained by "click" grafting of azide-modified (S)-camptothecin and alkyne-modified dextrans. Two series based on 10 kDa and 70 kDa dextrans were prepared with a degree of substitution of (S)-camptothecin between 3.1 and 10.2%. The binding properties with ß-cyclodextrin and ß-cyclodextrin polymers were measured by isothermal titration calorimetry and fluorescence spectroscopy, showing no binding with ß-cyclodextrin but high binding with ß-cyclodextrin polymers. In aqueous solution nanoparticles were formed from association between the (S)-camptothecin-dextran polymers and the ß-cyclodextrin polymers.

Effect of torsional isomerization and inclusion complex formation with cucurbit[7]uril on the fluorescence of 6-methoxy-1-methylquinolinium.

Inclusion of 6-methoxy-1-methylquinolinium (C1MQ) in the cavity of cucurbit[7]uril (CB7) was studied by absorption, fluorescence, NMR and isothermal calorimetric methods in aqueous solution at 298 K. The free C1MQ exhibited dual-exponential fluorescence decay kinetics due to the two torsional isomers differing in the orientation of the methoxy moiety relative to the heterocyclic ring. The enthalpy-driven encapsulation of the heterocycle in CB7 led to a very stable 1 : 1 complex with a binding constant of (2.0 ± 0.4) × 10(6) M(-1). The rate of C1MQ-CB7 complex dissociation was found to be comparable to the NMR timescale. Because the methoxy moiety is oriented outward from the host, its s-cis-s-trans isomerization is slightly affected by the confinement. Inclusion complex formation significantly slowed down the photoinduced electron transfer from I(-) and N3(-) to the singlet-excited C1MQ, but did not preclude the reaction because long distance electron transfer occurred through the wall of the CB7 macrocycle. Due to the large difference in the quenching rate constant for free and encapsulated forms, C1MQ is an excellent probe for the study of the inclusion of nonfluorescent compounds in CB7 in the presence of Cl(-) or Br(-).

Novel phosphorus-containing cyclodextrin polymers and their affinity for calcium cations and hydroxyapatite.

Novel phosphorous-containing ß-cyclodextrin (ßCD) polymers (CDP) were synthesized easily under "green chemistry" conditions. A simple polycondensation between the hydroxyl groups of ßCD and non-toxic sodium trimetaphosphate (STMP) under basic conditions led to soluble, non-reticulated CDPs with molecular weights (Mw) higher than 10(4) g mol(-1), the actual value depending on the NaOH:ßCD and STMP:ßCD weight ratios. The presence of both ßCD and phosphate groups in the polymer allows for strong interactions with amphiphilic probes, such as 1-adamantyl acetic acid, or with divalent cations, such as Ca(2+), whose strengths were characterized by isothermal titration microcalorimetry. The obtained phosphated compounds also display high affinity towards hydroxyapatite (HA), leading to HA nanoparticles that could easily be recovered by CDPs, as demonstrated by transmission electron microscopy and quantitative determination of the total amount of phosphated molecules fixed on HA.

4-Sulfonatocalix[6]arene-induced aggregation of ionic liquids.

The interaction of 4-sulfonatocalix[6]arene (SCX6) macrocycle with 1-alkyl-3-methylimidazolium type of ionic liquids possessing dodecyl, tetradecyl, or hexadecyl substituent was studied in aqueous solution at 298 K. Host-guest complexation promoted the spontaneous self-assembly into nanoparticles of 7:1 ionic liquid:SCX6 stoichiometry. Positively charged and stable nanoparticles were produced in solutions of 7-200-fold excess of ionic liquid as compared to the amount of SCX6. The negatively charged nanoparticles formed in solutions having 2-7 ionic liquid:SCX6 molar ratios evolved into larger species. The stability of the nanoparticles increased with the lengthening of aliphatic chain of the ionic liquid. Cryo-TEM experiments showed dense particles generally with spherical shape and multilayered structure, which has been confirmed by small-angle neutron scattering.

Segmental motions of poly(ethylene glycol) chains adsorbed on Laponite platelets in clay-based hydrogels: a NMR investigation.

The segmental dynamics of poly(ethylene glycol) (PEG) chains adsorbed on the clay platelets within nanocomposite PEG/Laponite hydrogels was investigated over the tens of microseconds time scale, using combined solution and solid-state NMR approaches. In a first step, the time evolution of the molecular mobility displayed by the PEG chains following the addition to a Laponite aqueous dispersion was monitored during the aggregation of the clay disks and the hydrogel formation, by means of (1)H solution-state NMR. Part of the PEG repeat units were found to get strongly constrained during the gelation process. Comparisons between this time evolution of the PEG local dynamics in the PEG/Laponite/water systems and the increase of the macroscopic storage shear modulus, mainly governed by the assembling of the Laponite disks, indicate that the slowing down of the segmental motions arises from adsorbed PEG repeat units or chain portions strongly constrained between aggregated clay layers. In a second step, after completion of the gelation process, the molecular motions of the adsorbed PEG chains were probed by (1)H solid-state NMR spectroscopy. (1)H double-quantum experiments indicate that the adsorbed PEG repeat units, though reported to be frozen over a few tens of nanoseconds, still display significant reorientational motions over the tens of microseconds time scale. Using a comparison with a model system of amorphized PEG chains, the characteristic frequency of these segmental motions was found to range between 78.0 kHz and 100.7 MHz at 300 K. Interestingly, at this temperature, the level of reorientational motions detected for these adsorbed PEG chain portions was found to be as restricted as the one of bulk amorphous PEG chains, cooled at a slightly lower temperature (about 290 K).

Cyclodextrin polymer nanoassemblies: strategies for stability improvement.

The main goal of this work was to develop two strategies for stabilization of nanoassemblies made of ß-cyclodextrin polymer and amphiphilic dextran associated through host-guest complexes. The first strategy was to coat the nanoassemblies with a dextran derivative bearing adamantyl anchoring groups and hydrophilic poly(ethylene oxide-co-propylene oxide) side chains to increase the steric repulsion between the nanoassemblies. The second strategy developed was to post-reticulate the nanoassemblies upon UV irradiation. Photo-cross-linkable nanoassemblies have been prepared from new host or guest polymers bearing allylether or methacrylate groups. The modified nanoassemblies have been characterized by dynamic light scattering as a function of time and for various salt and competitor concentrations. The results of the first strategy show an improvement of shelf stability and resistance at relatively low concentrations of competitors. The second strategy is the most efficient in providing good shelf stability, much larger than with the first strategy, together with a large resistance to dissociation in presence of competitors.

Smart DNA vectors based on cyclodextrin polymers: compaction and endosomal release.

PURPOSE: Neutral ß-cyclodextrin polymers (polyßCD) associated with cationic adamantyl derivatives (Ada) can be used to deliver plasmid DNA into cells. In absence of an endosomolytic agent, transfection efficiency remains low because most complexes are trapped in the endosomal compartment. We asked whether addition of an imidazole-modified Ada can increase efficiency of polyßCD/cationic Ada-based delivery system. METHODS: We synthesized two adamantyl derivatives: Ada5, which has a spacer arm between the Ada moiety and a bi-cationic polar head group, and Ada6, which presents an imidazole group. Strength of association between polyßCD and Ada derivatives was evaluated by fluorimetric titration. RESULTS: Gel mobility shift assay, zeta potential, and dark field transmission electron microscopy experiments demonstrated the system allowed for efficient DNA compaction. In vitro transfection experiments performed on HepG2 and HEK293 cells revealed the quaternary system polyßCD/Ada5/Ada6/DNA has efficiency comparable to cationic lipid DOTAP. CONCLUSION: We successfully designed fine-tuned DNA vectors based on cyclodextrin polymers combined with two new adamantyl derivatives, leading to significant transfection associated with low toxicity.

Size-controlled nanoassemblies based on cyclodextrin-modified dextrans.

Nanoassemblies formed by host/guest interactions between two polymers in aqueous media are studied. Two types of polymers with the same dextran backbone are modified with adamantyl or ßCD groups. The sizes of the spontaneously formed nanoassemblies depend on the ßCD:Ada ratio and on the total concentration and composition of the mixtures. The results can be rationalized by assuming a core/shell structure of the nanoassemblies, the core resulting from associative phase separation of the two polymers and being stabilized by an external shell made of Ada-grafted dextran and containing ions adsorbed from the solution. Hydrophobic compounds such as benzophenone can be incorporated efficiently without inducing changes in properties of the nanoassemblies.

Facile synthesis of beta-cyclodextrin-dextran polymers by "click" chemistry.

Three series of novel water-soluble beta-cyclodextrin-dextran polymers have been prepared by "click" chemistry. The polymers were synthesized from alkyne-modified dextrans (AMDs) onto which mono-6-O-deoxy-monoazido-betaCD (N3betaCD) was grafted by a copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The polymers have been characterized by NMR spectroscopy and size exclusion chromatography (SEC). The binding properties have been characterized by isothermal titration calorimetry (ITC) and show excellent accessibility of the betaCDs.

Associative network based on cyclodextrin polymer: a model system for drug delivery.

Associative networks have been elaborated by mixing in aqueous media a cyclodextrin polymer to a dextran bearing adamantyl groups. The two polymers interact mainly via inclusion complexes between adamantyl groups and cyclodextrin cavities, as evidenced by the high complexation constants determined by isothermal titration microcalorimetry (approximately 10(4) L mol(-1)). Additional interaction mechanisms participating in the strength of the network, mainly hydrogen bonding and electrostatic interactions, are sensitive to the pH and ionic strength of the medium, as shown by pH-dependent rheological properties. The loading and release of an apolar model drug, benzophenone, has been studied at two pH values and different cyclodextrin polymer content. Slow releases have been obtained (10-12 days) with slower kinetics at pH 2 than at pH 7. Analysis of the experiments at pH 7 shows that drug release is controlled both by diffusion in the network and by inclusion complex interactions with cyclodextrin cavities.