Aggregation Of Cyclodextrins Research Articles

Development of dexamethasone suspension eye drops: A comparative investigation of ternary and quaternary cyclodextrin aggregates

Development of dexamethasone suspension eye drops: A comparative investigation of ternary and quaternary cyclodextrin aggregates

An Optimization Procedure for Preparing Aqueous CAR/HP-CD Aggregate Dispersions.

β-Carotene is a very important molecule for human health. It finds a large application in the food industry, especially for the development of functional foods and dietary supplements. However, β-carotene is an unstable compound and is sensitive to light, temperature, and oxygen. To overcome those limitations, various delivery systems were developed. The inclusion of β-carotene by cyclodextrin aggregates is attractive due to non-toxicity, low hygroscopicity, stability, and the inexpensiveness of cyclodextrins. In this study, β-carotene/2-hydroxypropyl-β-cyclodextrin aggregates were prepared based on the procedure of the addition of β-carotene in an organic solvent to the hot water dispersion of 2-hydroxypropyl-β-cyclodextrin and the following instant evaporation of the organic solvent. The best conditions for the aggregate preparation were found to be as follows: 25% concentration of 2-hydroxypropyl-β-cyclodextrin in water, 65 °C temperature, and acetone for β-carotene dissolution. The efficiency of entrapping was equal to 88%. The procedure is attractive due to the short time of the aggregate preparation.

Do the solvent properties affect the propensity for self-association of α-cyclodextrin? Insights from NMR self-diffusion

Whether cyclodextrins (CDs) self-aggregate or not in solution is an interesting and timely scientific question. Yet, we are far from a scientific consensus as regards the nature of the phenomenon. Those who are in favor of the formation of CD aggregates justify the phenomenon by the presence of H-bonds, occurring between the hydroxyl groups located at both rims of cyclodextrins. To gain further insight with regard to the importance of these intermolecular CD-CD interactions, a systematic study of 1H NMR self-diffusion of α-cyclodextrin in binary mixtures of deuterated DMSO and water, at different mole fractions, has been carried out. The choice of these solvents was made based on their different degree of polarity and the fact that they are miscible at any molar ratio. The experimental α-CD diffusion coefficients scale with the solution viscosity. Moreover, hydrodynamic radii of α-CD are independent of the solvent composition. No evidence of α-cyclodextrin aggregation at any DMSO mole fraction is found. Finally, experimental diffusion data are compared with those obtained from atomic level hydrodynamic calculations.In addition, diffusion coefficients of heavy water and DMSO in binary mixed solvents are also measured and analyzed. The obtained diffusion coefficients for DMSOd6 and D2O show a minimum at the eutectic composition and depend on the solution viscosity. The experimental results are compared with published molecular dynamic simulations.

Interaction of native CDs and their hydroxypropyl derivatives with parabens in aqueous solutions. Part 2: evaluation of paraben/cyclodextrin complex aggregation

Cyclodextrins (CDs) and their inclusion complexes are known to self-assemble in aqueous solutions to form aggregates and the physicochemical characteristics of guest molecules have been linked to the aggregate formation. A series of parabens was selected as model compounds due to their small size (aromatic ring fits in the cavity) and different side chain length. In Part 1 it was demonstrated that CDs and parabens form a range of soluble and insoluble complexes dependent on the type of CD (native or hydroxypropylated αCD, βCD or γCD) and the length of the alkyl residue of the parabens. Furthermore, phase-solubility studies suggested that higher order complexes (e.g., aggregates) were formed. Here we apply osmometry and permeation studies to evaluate if and how the alkyl chain length of the parabens influences the process of aggregate formation. Furthermore, the possible effect of CD aggregates on permeation profile of parabens is also elucidated. Changes in osmometry correlate with the type pf phase-solubility profile. For AL-types total osmolality remained unchanged throughout experiment, while for B-types the osmolality of systems displayed significant changes mainly due to precipitation of poorly-soluble complexes. The permeation method is an effective and useful method to detect and evaluate self-assembly of CDs and to detect aggregate formation in aqueous γCD and HPβCD solutions containing parabens. Generally, all parabens modified the natural aggregation behavior of HPβCD and γCD as the apparent critical aggregation concentration (cac) values for paraben/CD systems decreased compared to those of pure aqueous CD solutions. The longer the alkyl side chain, the greater was the promotion of aggregates formation (methyl < ethyl < propyl < butyl) and, consequently, more and larger aggregates are formed. These superstructures are responsible for the observed changes in apparent cac and flux values, as well as, for the observed slopes greater than unity for the phase-solubility diagrams.

Inclusion complexes and self-assembled cyclodextrin aggregates for increasing the solubility of benzimidazoles

Albendazole and fenbendazole are imidazole derivatives that exhibit broad spectrum activity against parasites, but the low solubility of these drugs considerably reduces their effectiveness. Complexation of albendazole and fenbendazole with cyclodextrins (β-cyclodextrin and hydroxypropyl-β-cyclodextrin) in both water and an aqueous solution of polyvinylpyrrolidone (PVP-k30) was studied to determine if it could increase the solubility and dissolution rate of the drugs. In an aqueous solution, β-cyclodextrin increased the solubility of albendazole from 0.4188 to ∼93.47 µg mL-1 (223×), and of fenbendazole from 0.1054 to 45.56 µg mL-1 (432×); hydroxypropyl-β-cyclodextrin, on the other hand, increased solubility to ∼443.06 µg mL-1 (1058×) for albendazole and ∼159.36 μg mL-1 (1512×) for fenbendazole. The combination of hydroxypropyl-β-cyclodextrin and polyvinylpyrrolidone enabled a solubility increase of 1412× (∼591.22 µg mL-1 ) for albendazole and 1373× (∼144.66 µg mL-1 ) for fenbendazole. The dissolution rate of the drugs was significantly increased in binary and ternary systems, with hydroxypropyl-β-cyclodextrin proving to be more effective. The presence of the water-soluble PVP-k30 increased the dissolution rate and amorphization of the complexes. Analysis of the changes in displacement and the profile of the cyclodextrin bands in the 1 H NMR spectra revealed a molecular interaction and pointed to an effective complexation in the drug/cyclodextrin systems. Monomeric forms and nanoclusters of cyclodextrins were observed in the drug/cyclodextrin systems, suggesting that the increase in solubility of the drugs in the presence of cyclodextrins should not be attributed only to the formation of inclusion complexes, but also to the formation of cyclodextrin aggregates.

Studies on the antibacterial activity of water-soluble iron oxide nanoparticle- [formula omitted]-cyclodextrin aggregates against selected human pathogenic bacteria

Increased microbial resistance being a serious issue, we synthesized iron oxide nanoparticle-encapsulated β-cyclodextrin with potential antibacterial properties. Since iron is already a biologically significant trace metal, iron and its oxides are always significant in the field of medicine. In the present study, we have successfully synthesized α-Fe2O3 nanoparticles encapsulated into a supramolecular host system, β-cyclodextrin. The products were characterized using UV/visible, photoluminescence and FTIR spectroscopic techniques. The particle size and crystalline nature were investigated using XRD measurements. The surface morphology and topography of the aggregates were studied using scanning and high-resolution transmission electron microscopies. The human pathogenic bacterial strains S.aureus, K.Pneumoniae and S.typhi were randomly selected for the study based on their pathogenic effect on humans. MIC values were also determined for each species.

Disruption of α- and γ-cyclodextrin aggregates promoted by chaotropic agent (urea)

Over the years several authors have reported that cyclodextrins (CDs), especially the native ones (i.e. αCD, βCD and γCD), spontaneously form aggregates in aqueous solutions. Sometimes this phenomenon can be advantageous as these aggregates can be the base of novel drug delivery systems but also as detrimental since it leads to formulation instability due to presence of visible microparticles that are, for example, unacceptable in parenteral dosage forms. The need of controlling this phenomenon sparked us to study the influence of water structure modifiers agents (e.g., urea) on the CD self-assembly process.Urea does not interact with CDs as 1H NMR studies have revealed, acting only by disruption of aggregate formation through hindering formation of H-bonds. This was actually observed visually as decreased haziness of aqueous αCD and γCD solutions with increased urea concentration. Permeation studies of aqueous αCD and γCD solutions, in presence or absence of urea, through 3.5–5 kDa semi-permeable membrane have proven to be a reliable analytical method to detect and quantify changes in CD aggregation. Permeation data strongly suggests that the CD aggregation decreases with increasing urea concentration. The presence of urea leads to smaller aggregates and increased apparent cac (critical aggregation concentration) values for both αCD and γCD. Urea is not an approved pharmaceutical excipient. However, the study gives a scientific insight into formation and stability of the CD aggregates and how formation of these super structures can be modulated by addition of chaotropic agents.

Self-Assembly of α-Cyclodextrin and β-Cyclodextrin: Identification and Development of Analytical Techniques

Recently, it has been shown that cyclodextrins (CDs) self-assemble in aqueous solutions to form aggregates. Such aggregation can give rise to formation of particulate matter in aqueous solutions. However, the analytical methodology available to detect and quantify these aggregates is still quite inadequate. Here, 5 different methods for evaluation of CD aggregate formation and determination of the critical aggregation concentration are evaluated: osmometry, viscosity, surface tension, dynamic light scattering, and permeability studies. Both the viscosity and surface tension methods applied were inadequate for aggregate detection, whereas the osmometry method can be used to study CD aggregation but with some limitations. Dynamic light scattering has also some limitations although it can be applied to detect CD aggregates and to estimate their hydrodynamic diameter. Overall, permeation studies proved to be the best method to detect and determine critical aggregation concentration. These results suggested that β-cyclodextrin (βCD) has higher tendency to aggregate than α-cyclodextrin (αCD). Filtration of αCD and βCD solutions affected the aggregate size distribution by breaking larger aggregates in to smaller ones that then reassembled to regenerate the larger ones upon storage. The osmolality studies showed that in aqueous αCD and βCD solutions, solute-solute interactions are favored over solute-solvent interactions with consequent CD aggregate formation.

Molecular Dynamics of Cyclodextrins in Water Solutions from NMR Deuterium Relaxation: Implications for Cyclodextrin Aggregation.

The aggregation of the most common natural cyclodextrins (α-, β-, and γ-) in aqueous solutions is addressed by studying the CD-CD interactions using deuterium relaxation rates for deuterium labeled CDs. Relaxation times (T1) and their corresponding relaxation rates (R1 = 1/T1) provide information about the rotational correlation times of CDs and serve as a proxy for solute-solute interactions. Measured T1's for α-, β-, and γ-CD at the lowest CD concentrations were in agreement with predictions of a hydrodynamic model for toroids, in particular with regard to the dependence of T1 on CD size. On the other hand, the dependence of T1's with respect to the increase in CD concentration could not be explained by hydrodynamic or direct interaction between CD molecules, and it is suggested that there is an equilibrium between monomeric and dimeric CD to account for the observed concentration dependence. No evidence in favor of large aggregates of CDs involving a non-negligible fraction was found for the investigated CDs.

The impact of guest compounds on cyclodextrin aggregation behavior: A series of structurally related parabens

Several studies have demonstrated the presence of aggregates in aqueous cyclodextrin containing solutions. The presence of guest compounds has been shown to influence this cyclodextrin aggregation process. In an attempt to gain insight into the effect of the physicochemical properties of the guest compound on 2-hydroxypropyl-β-cyclodextrin aggregation formation, a series of structurally related parabens was selected as model compounds. Using nuclear magnetic resonance spectroscopy and phase solubility studies, these parabens, differing only in side chain length, were demonstrated to form inclusion complexes with 2-hydroxypropyl-β-cyclodextrin. Additional techniques were subsequently applied to evaluate the aggregation behavior of this cyclodextrin in presence of the selected parabens. Solutions containing a broad range of 2-hydroxypropyl-β-cyclodextrin concentrations were saturated with the guest compounds and were used as test media. Results obtained from dialysis experiments, dynamic light scattering and mass spectrometry revealed a positive effect of the side chain length of the parabens on aggregate formation: in presence of heptylparaben, more and larger aggregates were observed than in presence of parabens with shorter side chains such as methyl- and butylparaben. No clear connection could be demonstrated between the cyclodextrin concentration and the extent of aggregate formation in presence of the guest compound.

A study of the aggregation of cyclodextrins: Determination of the critical aggregation concentration, size of aggregates and thermodynamics using isodesmic and K2–K models

The aggregation of three different cyclodextrins (CDs): 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), 2-hydroxypropyl-γ-cyclodextrin (HP-γ-CD) and sulfobutylether-β-cyclodextrin (SBE-β-CD) was studied. The critical aggregation concentration (cac) of these three CDs is quite similar and is situated at ca. 2% (m/v). There was only a small difference in the cac values determined by DLS and 1H NMR. DLS measurements revealed that CDs in solution have three size populations wherein one of them is that of a single CD molecule. The size of aggregates determined by TEM appears to be similar to the size of the aggregates in the second size distribution determined by DLS. Isodesmic and K2–K self-assembly models were used for studying the aggregation process of HP-β-CD, HP-γ-CD and SBE-β-CD. The results showed that the aggregation process of these CDs is a cooperative one, where the first step of aggregation is less favorable than the next steps. The determined thermodynamic parameters showed that the aggregation process of all three CDs is spontaneous and exothermic and it is driven by an increase of the entropy of the environment.

Characterisation of aggregates of cyclodextrin-drug complexes using Taylor Dispersion Analysis

There is a need to understand the nature of aggregation of cyclodextrins (CDs) with guest molecules in increasingly complex formulation systems. To this end an innovative application of Taylor dispersion analysis (TDA) and comparison with dynamic light scattering (DLS) have been carried out to probe the nature of ICT01-2588 (ICT-2588), a novel tumor-targeted vascular disrupting agent, in solvents including a potential buffered formulation containing 10% hydroxypropyl-β-cyclodextrin. The two hydrodynamic sizing techniques give measurement responses are that fundamentally different for aggregated solutions containing the target molecule, and the benefits of using TDA in conjunction with DLS are that systems are characterised through measurement of both mass- and z-average hydrodynamic radii. Whereas DLS measurements primarily resolve the large aggregates of ICT01-2588 in its formulation medium, methodology for TDA is described to determine the size and notably to quantify the proportion of monomers in the presence of large aggregates, and at the same time measure the formulation viscosity. Interestingly TDA and DLS have also distinguished between aggregate profiles formed using HP-β-CD samples from different suppliers. The approach is expected to be widely applicable to this important class of drug formulations where drug solubility is enhanced by cyclodextrin and other excipients.

Molecular dynamics simulation of cyclodextrin aggregation and extraction of Anthracene from non-aqueous liquid phase

Cyclodextrin (CD) extraction is widely used for the remediation of polycyclic aromatic hydrocarbons (PAH) pollution, but it remains unclear about the influence of CD aggregation on the PAH transport from non-aqueous liquid phase to water. The atomistic adsorption and complexation of PAHs (32 anthracenes) by CD aggregates (48 β-cyclodextrins) were studied by molecular dynamics simulations at hundreds of nanoseconds time scale. Results indicated that high temperature promoted the βCD aggregation in bulk oil, which was not found in bulk water. Nevertheless, the fractions of anthracenes entrapped inside the βCDs cavity in both scenarios were significantly increased when temperature increased from 298 to 328K. Free energy calculation for the sub-steps of CD extraction demonstrated that the anthracenes could be extracted when the βCDs arrived at the water-oil interface or after the βCDs entered the bulk oil. The former was kinetic-controlled while the latter was thermodynamic-limited process. Results also highlighted the formation of porous structures by CD aggregates in water, which was able to sequestrate PAH clusters with the size obviously larger than the cavity diameter of individual CD. This provided an opportunity for the extraction of recalcitrant PAHs with molecular size larger than anthracenes by cyclodextrins.

Do Cyclodextrins Aggregate in Water? Insights from NMR Experiments.

One decade ago Bonini et al. [Langmuir 2006, 22, 1478-1484] reported the occurrence of aggregates of β-cyclodextrin in aqueous solutions with sizes in the range from 90 nm to a few micrometers. The experimental technique used was cryo-TEM. This work followed a number of previous studies involving other physical parameters, such as viscosities and activity coefficients, the results of which were interpreted in terms of self-aggregation of cyclodextrins. Since then, the ability of cyclodextrins to self-assemble were often used to explain and rationalize the supramolecular mechanisms involving cyclodextrins. Here, the question of aggregation of native cyclodextrins (α-, β-, and γ-) in aqueous solutions is addressed by using (1)H NMR techniques, including NMR diffusometry, relaxometry, and proton peak intensities. Within the detection limit of the NMR experiments, no aggregates of cyclodextrin were observed. If aggregates are present, the fraction of cyclodextrin in aggregates is quite small-less than 1%. However, we cannot exclude the presence of transient clusters involving several cyclodextrin molecules where the lifetime of the cluster is short.

Surface adsorption and bulk aggregation of cyclodextrins by computational molecular dynamics simulations as a function of temperature: α-CD vs β-CD.

The structural simplicity of native cyclodextrins (CDs) contrasts with their complex behavior in the bulk of aqueous solutions, mainly when they are combined with other cosolutes. Many scientific and industrial applications based on these molecules are supported only by empirical information. The lack of fundamental knowledge, which would allow one to rationally optimize many of these applications, is notable mainly at the solution/air interface. Basic information on phenomena such as the spontaneous adsorption of native CDs or on the structure of CD aggregates in the bulk solution is really scarce. In order to fill these gaps, a detailed computational study on the adsorption and aggregation of α- and β-CDs as a function of temperature is presented here. Our simulations reproduce, at atomic resolution, the experimentally observed much higher ability of β-CD to aggregate compared to that of α-CD at 298 K, as well as their dependence on temperature. The adsorption of both individual CDs and small CD aggregates (up to 20 molecules) to the solution/air interface is found to be negligible. 0.8 μs long trajectories of single CD molecules in aqueous solution reveal that the main differences in the behavior of both CDs are their flexibility, higher for β-CD, and the occupancy of individual intramolecular hydrogen bonds that is significantly longer for the same cyclodextrin. The aggregation pattern of α- and β-CDs is followed at the hundreds of ns time scale, allowing both the spontaneous self-assembly of cyclodextrins and their redistribution along the aggregates to be observed. This is the first attempt to study the adsorption and aggregation of native cyclodextrins by atomistic molecular dynamics simulations.

Electrospinning of nanofibers from non-polymeric systems: Electrospun nanofibers from native cyclodextrins

Electrospinning of nanofibers from non-polymeric systems is rather challenging, yet in this study, we have successfully performed electrospinning of nanofibers from two of the native cyclodextrins (CDs); α-CD and β-CD. Electrospinning was carried out for highly concentrated solutions of α-CD (120% up to 160%, w/v) and β-CD (120% up to 150%, w/v) in basic aqueous system. At optimal concentration level, the electrospinning of CD solutions yielded bead-free uniform CD nanofibers without using carrier polymeric matrix. Similar to polymeric systems, the electrospinning of CD solutions resulted in different morphologies and average fiber diameters depending on the CD type and CD concentration. The dynamic light scattering (DLS) and rheology measurements were performed in order to examine the electrospinnability of CD solutions. The existence of CD aggregates via hydrogen bonding and very high solution viscosity and viscoelastic solid-like behavior of CD solutions were found to be the key factors for obtaining bead-free nanofibers from CDs. The addition of urea disrupted CD aggregates and lowered the viscosity significantly, and therefore, the urea-added CD solutions yielded beaded fibers and/or beads. Although the as-received CDs in powder form are crystalline, the structural analyses by XRD and HR-TEM indicated that electrospun CD nanofibers have amorphous characteristic without showing any particular orientation or crystalline aggregation of CD molecules.

Host–guest system of etodolac in native and modified β-cyclodextrins: preparation and physicochemical characterization

Etodolac, being a practically insoluble candidate, exhibits certain toxic effects and a limited bioavailability. Upon chronic use, it causes gastro-intestinal injury and increases the risk of ulcer complications. The approach of this study was to improve the physicochemical properties of the drug utilizing complexation phenomenon with β-, methyl-β- and hydroxypropyl-β-cyclodextrins, which may enhance the aqueous solubility and dissolution rate of etodolac, in an effort to increase oral bioavailability. In certain instances, this approach can be used to increase drug solubility, improve organoleptic properties and maximize the gastrointestinal tolerance by reducing drug irritation after oral administration. Differential UV measurements as well as continuous variation plots revealed the formation of equimolar complex with hydroxypropyl-β-cyclodextrin and 1:2 complexes with β-cyclodextrin and its methyl derivative. Differential scanning calorimetry (DSC), X-ray and FT-IR measurements were applied to prove inclusion complex formation and characterize the complexes. These results lend support to the idea that solubilization of etodolac is mainly related to inclusion complex formation and to a lesser extent to cyclodextrin aggregates. Understanding the factors that influence the performance of etodolac, will allow us to state that molecular encapsulation of the drug and other modifications with appropriate hydroxylation or methylation of parent β-cyclodextrin is able to overcome its problems and facilitate safe and efficient delivery of the drug.

Electrospinning of nanofibers from non-polymeric systems: polymer-free nanofibers from cyclodextrin derivatives

High molecular weight polymers and high polymer concentrations are desirable for the electrospinning of nanofibers since polymer chain entanglements and overlapping are important for uniform fiber formation. Hence, the electrospinning of nanofibers from non-polymeric systems such as cyclodextrins (CDs) is quite a challenge since CDs are cyclic oligosaccharides. Nevertheless, in this study, we have successfully achieved the electrospinning of nanofibers from chemically modified CDs without using a carrier polymer matrix. Polymer-free nanofibers were electrospun from three different CD derivatives, hydroxypropyl-β-cyclodextrin (HPβCD), hydroxypropyl-γ-cyclodextrin (HPγCD) and methyl-β-cyclodextrin (MβCD) in three different solvent systems, water, dimethylformamide (DMF) and dimethylacetamide (DMAc). We observed that the electrospinning of these CDs is quite similar to polymeric systems in which the solvent type, the solution concentration and the solution conductivity are some of the key factors for obtaining uniform nanofibers. Dynamic light scattering (DLS) measurements indicated that the presence of considerable CD aggregates and the very high solution viscosity were playing a key role for attaining nanofibers from CD derivatives without the use of any polymeric carrier. The electrospinning of CD solutions containing urea yielded no fibers but only beads or splashes since urea caused a notable destruction of the self-associated CD aggregates in their concentrated solutions. The structural, thermal and mechanical characteristics of the CD nanofibers were also investigated. Although the CD derivatives are amorphous small molecules, interestingly, we observed that these electrospun CD nanofibers/nanowebs have shown some mechanical integrity by which they can be easily handled and folded as a free standing material.

Temperature-responsive inclusion complex of cationic PNIPAAM diblock copolymer and γ-cyclodextrin

Aqueous mixtures of γ-cyclodextrin (γ-CD) and the thermosensitive cationic diblock copolymer poly(N-isopropylacrylamide)-b-poly(3-acrylamidopropyl)trimethylammonium chloride (PNIPAAM24-b-PAMPTAM(+)9) or the PNIPAAM homopolymer PNIPAAM47 have been investigated using various experimental methods. Solid γ-CD–polymer inclusion complexes (pseudopolyrotaxanes) form at ambient temperatures in fairly concentrated CD solutions. The NMR measurements showed that the stoichiometry of the inclusion complexes is close to two NIPAAM units per CD molecule. The cationic block of the copolymer is not incorporated into the CD cavity. Synchrotron radiation X-ray diffraction spectra of the solid inclusion complexes indicate a compact columnar structure of CD molecules threaded onto the PNIPAAM chains. In water, square-shaped cyclodextrin aggregates were found to co-exist with single cyclodextrin molecules. In mixed solutions of γ-CD and PNIPAAM24-b-PAMPTAM(+)9 these aggregates disintegrate with time as inclusion complexes are formed and the kinetics was studied using time-resolved static and dynamic light scattering and cryo-TEM. Steady-state fluorescence spectroscopy measurements reveal that the CD molecules dethread from the PNIPAAM chains upon increasing the temperature to 40 °C, which is above the lower critical solution temperature of PNIPAAM.

Modulation of Small Molecule Induced Architecture of Cyclodextrin Aggregation by Guest Structure and Host Size

A small molecule based on bisphenylethynyl amide meta linked to 2,6-pyridine can induce cyclodextrin (CD) aggregation through a possible 1:3 guest–host motif. Most of the small molecules induce CD nanotubular bundles principally through 1:2 guest–host unit capsules and aggregate through hydrogen bonding among the hydroxyl groups present on the rims of the CD molecules. The N,N-dimethyl aminopropyl carboxamide side chain and the central pyridine ring of 6-bromo-2-phenylethylaminopyridine (BPEAP) induces nanotubular bundles with α-CD and laminar bundles with β- and γ-CDs, which, as a consequence, may result in formation of pores in the aggregates that can find wide applications in biological storage machinery. The stoichiometry of the ingredients of the unit capsules has been evidenced by Job’s plot. The size-dependent suprastructures induced by BPEAP have been studied by steady state and time-resolved fluorescence spectroscopy and atomic force microscopy.