Probe-Induced Self-Aggregation of γ-Cyclodextrin: Formation of Extended Nanotubular Suprastructure (original) (raw)
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Fragmentation of molecule-induced γ-cyclodextrin nanotubular suprastructures due to drug dosage
Journal of Colloid and Interface Science, 2009
The guest-host concentration has already been proved to be a very important factor in the drug delivery process. In the present work we demonstrate the formation of compound induced c-cyclodextrin nanotubular suprastructure. The nanotubes formed are found to be highly sensitive to the concentration of the guest molecule. The increasing concentration of the compound in solution initiates a competition toward their existence inside the core of the nanotubes affecting the extent of nanotubular cluster formation. The hydrogen bonding responsible for the building of the cyclodextrin nanotubes is found to be partially disrupted because of this increasing competition. The continuous replacement of the guest molecules inside the nanochannels is supposed to be responsible for the instability in some of the hydrogen bondings that develop during the primary and the secondary interactions between the formed nanotubes resulting into fragmentation of the suprastructures. The steady state and time-resolved fluorescence experiments coupled with fluorescence anisotropy and atomic force microscopy illustrate the guest concentration dependence of the formation of the c-cyclodextrin nanotubes.
Cyclodextrin-based self-assembled nanotubes at the water/air interface
The Journal of …, 2007
Native R-cyclodextrin (R-CD) is found to spontaneously form films at aqueous solution/air interfaces. Shaperesponse measurements to volume perturbations on drops hanging from a capillary indicate that temperature and sodium dodecyl sulfate (SDS) concentration strongly modify the viscoelastic properties of such films. By using isothermal titration calorimetry (ITC), Brewster angle microscopy (BAM), atomic force microscopy (AFM), and molecular dynamics (MD) simulations, it is shown that the films consist of self-assembled nanotubes whose building blocks are cyclodextrin dimers (R-CD 2 ) and R-CD 2 -SDS 1 complexes. B J. Phys. Chem. B Letters
Journal of Photochemistry and Photobiology A-chemistry, 2009
The formation of nanotubes of -cyclodextrins (-CD) and their secondary assembly induced by trans-2-[4-(dimethylamino)styryl]benzothiazole (DMASBT) as a guest molecule has been explained using twisted intramolecular charge transfer (TICT) fluorescence, steady state fluorescence anisotropy, time-correlated single-photon counting fluorescence decay of DMASBT, atomic force microscopy and also transmission electron microscopy. It has been demonstrated that although at lower concentration of -CD, DMASBT molecules form simple adduct of 1:1 stoichiometry but they form extended nanotubes at relatively high concentration of -CD which further lead to the secondary assembly through intertubular hydrogen bondings forming rod-like structures. The changes in fluorescence properties of DMASBT yield critical aggregation concentration (CAC) of -CD very close to 2.5 mM. The extent of formation of these supramolecular structures is dependent on the concentration of guest molecule. It has been observed that perchlorate ion (ClO 4 − ) reduces the stability of supramolecular structures at higher concentration of it but at low concentration (<7 mM) it enhances the stability by providing the anchor sites for intermolecular hydrogen bonding between neighboring -CD molecules. The polarity and viscosity dependent TICT fluorescence characteristics of DMASBT are exploited to determine the micropolarity and microviscosity of environment around it inside the nanotubes.
Chemical Physics Letters, 2013
Steady state absorption, emission, and picosecond time resolved fluorescence and transmission electron microscopic (TEM) techniques have been exploited to substantiate and characterize the formation of a substrate-anchored b-cyclodextrin nanotubular suprastructure in aqueous medium. Experimental results reveal that suprastructure is originated from a purely ground state interaction between a newly developed bisindole based drug molecule namely 3,3 0-bis(indolyl)-4-chlorophenylmethane (BICPM) with b-cyclodextrin. The bound drug molecule is susceptible to be released out from the supramolecular complex in a controlled manner by the use of endogenous surfactants and is poised to serve a significant purpose in targeted drug delivery preferably at the intestinal region.
Self-assembled cyclodextrin aggregates and nanoparticles
International Journal of Pharmaceutics, 2010
a b s t r a c t Cyclodextrins (CDs) are widely used as enabling pharmaceutical excipients, mainly as solubilizing complexing agents. CDs are cyclic oligosaccharides with hydrophilic outer surface and a somewhat lipophilic central cavity. In aqueous solutions CDs are able to solubilize lipophilic drugs by taking up some lipophilic moiety of the drug molecule into the central cavity, i.e. through formation of hydrophilic inclusion complexes. Recently it has been observed that that other types of CD complexes, such as non-inclusion complexes, are also participating in the CD solubilization of poorly soluble drugs. However, in aqueous solutions CDs are also able self-assemble to form nanosized aggregates that can contribute to their solubilizing properties. At low CD concentrations (at about 1%, w/v) the fraction of CD molecules forming aggregates is insignificant but the aggregation increases rapidly with increasing CD concentration. Also, formation of CD complexes can increase the tendency of CDs to form aggregates and can lead to formation of micellar-type CD aggregates capable to solubilize poorly soluble compounds that do not readily form inclusion complexes. In this article formation of CD aggregates and CD nanoparticles is reviewed with emphasis on the physicochemical properties of self-assembled CDs and CD complexes.
Characterization and control of the aggregation behavior of cyclodextrins
Photon correlation spectroscopy has been employed for the purpose of characterizing the aggregation behavior of cyclodextrin molecules in aqueous solutions. This optical method is generally intended to study particle size distribution of colloidal particles, associates and macromolecules. Herein we report on some general methodological issues of photon correlation spectroscopy aiming to illustrate aggregated and non-aggregated state of parent cyclodextrins and cyclodextrin derivatives, such as (2-hydroxy)propyl-b-cyclodextrin and tetraamino rhodaminyl (2-hydroxypropyl)-b-cyclodextrin in different aqueous media. Based on particle size analysis data we have demonstrated that the tendency of cyclodextrin molecules to form aggregates may be controlled by temperature and by various additives, e.g. urea, citric acid and polyvinylpyrrolidone. In the case of (2-hydroxypropyl)-b-cyclodextrin the effect of degree of substitution was also studied.
Self-assembly of cyclodextrins: formation of cyclodextrin polymer based nanoparticles
2012
The design of functional cyclodextrin (CD) nanoparticles is a developing area in the field of nanomedicine. CDs can not only help in the formation of drug carriers but also increase the local concentration of drugs at the site of action. CD monomers form aggregates by self-assembly, a tendency that increases upon formation of inclusion complexes with lipophilic drugs. However, the stability of such aggregates is not sufficient for parenteral administration. In this review CD polymers and CD containing nanoparticles are categorized, with focus on self-assembled CD nanoparticles. It is described how the nanoparticles can be stabilized and tuned to have specific properties.
Journal of Colloid and Interface Science, 2010
Calorimetric titration technique using flow devices is generally used to understand the thermodynamics of nanotubular suprastructure formations, however high concentrations of the guest molecules used may disrupt the suprastructures. This report shows thermodynamic information can also be obtained by the implementation of fluorescence spectroscopy. Denaturants break nanotubular assembly created by the guest molecule leading to change in guest fluorescence on altering the denaturant concentration. This phenomenon can be monitored to get the relative change in enthalpy in the process of fragmentation of the nanotubular structures along with the change in the standard free energy. The fluorescence technique uses appropriate concentration of the guest molecules required to form nanotubular suprastructures.
Aggregation of Cyclodextrins: Fundamental Issues and Applications
Cyclodextrin - A Versatile Ingredient
The aggregation of cyclodextrins (CD) in aqueous solution is an old, yet still vastly unexplored topic that has been studied at least since the 1980s. At that time, few authors took into consideration the possibility of formation of aggregates for the interpretation of thermodynamic and thermophysical properties of CDs in aqueous solution. The aggregates appear at quite low CD concentrations and seem to encompass only a small number of CD molecules. They also occur in water in the presence of hydrophobic or amphiphilic moieties, including surfactants, assuming a preassembled state with the hydrophobic chains threading through one or two CDs. After a long period in which it has been neglected, CD aggregation is now a hot topic and one far from gathering consensus. In this chapter, a timely and critical review on the phenomenon of CD aggregation and the respective supramolecular properties, including some computational rationales, will be presented. A comprehensive summary of CD aggregates studied to date, indicating the formation conditions, characterization techniques, and applications, is also provided.
International Journal of Pharmaceutics, 2011
Recently it has been shown that aggregation of drug/cyclodextrin inclusion complexes is strongly influenced by the drug molecule in addition to self-assembling tendencies of the cyclodextrin itself in aqueous media. Whereas the mechanistic basis of cyclodextrin self-assembly is known, the driving forces for complex aggregation are still unknown. In the present study, the influence of temperature on hydrocortisone/2-hydroxypropyl--cyclodextrin complex aggregation is investigated as are influences associated with the addition of ethanol or water soluble polymers to the aqueous systems. Furthermore the effect of stirring on the aggregation is assessed. Size exclusion permeability studies were conducted to estimate complex aggregation tendencies. The results indicate that self-assembled complex aggregates are metastable and notably become smaller with increasing temperature and the addition of ethanol. Water soluble polymers also reduce the size of the complex aggregates. Specifically, hexadimethrine bromide had the greatest impact, since addition of this compound eliminated aggregates from the systems or reduced their size below the molecular weight cut-off of the sizing membrane (8 kDa). Similar observations are made when aqueous solutions of hydrocortisone and 2-hydroxypropyl--cyclodextrin are equilibrated by stirred.