Fluorescence Probe Technique Research Articles

In Situ Investigations on Cetyltrimethylammonium Surfactant/Silicate Systems, Precursors of Organized Mesoporous MCM-41-Type Siliceous Materials

Organized mesoporous silica (OMS) constitutes new materials with many potential applications. These materials with very well organized pores can be obtained by lowering the pH of precursor systems, i.e., highly alkaline silicate solutions containing cationic surfactants such as cetyltrimethylammonium bromide (CTAB) or chloride (CTAC). The precursor systems of OMS have been investigated prior to precipitation by in situ techniques. 29Si liquid-state NMR spectroscopy has been used to determine the type of silicate species in the investigated systems and how it is affected by the presence of the surfactant. Fluorescence probing techniques with the fluorescent probes pyrene and dipyrenylpropane have been used to study the variation of properties of the CTAB and CTAC micelles upon successive additions of a large excess of base (sodium hydroxide or tetramethylammonium hydroxide) and silicate (water glass or octameric species Si8O208-) as to generate the precursor systems that have the compositions that are used...

Drug release from thermo-responsive self-assembled polymeric micelles composed of cholic acid and poly(N-isopropylacrylamide).

Cholic acid, conjugated with amine-terminated poly(N-isopropylacrylamide) (abbreviated as CA/ATPNIPAAm), was synthesized by a N, N'-dicyclohexyl carbodiimide (DCC)-mediated coupling reaction. Self-assembled CA/ATPNIPAAm micelles were prepared by a diafiltration method in aqueous media. The CA/ATPNIPAAm micelles exhibited a lower critical solution temperature (LCST) at 31.5 degrees C. Micelle sizes measured by photon correlation spectroscopy (PCS) were approximately 31.6+/-5.8 nm. The CA/ATPNIPAAm micelles were spherical and their thermal size transition was observed by transmission electron microscope (TEM). A fluorescence probe technique was used for determining the micelle formation behavior of CA/ATPNIPAAm in aqueous solutions using pyrene as a hydrophobic probe. The critical micelle concentration (CMC) was evaluated as 8.9 x 10(-2) g/L. A drug release study was performed using indomethacin (IN) as a hydrophobic model drug. The release kinetics of IN from the CA/ATPNIPAAm micelles revealed a thermo-sensitivity by the unique character of poly(N-isopropylacrylamide) i.e. the release rate was higher at 25 degrees C than at 37 degrees C.

Clonazepam release from core-shell type nanoparticles of poly(ε-caprolactone)/poly(ethylene glycol)/poly(ε-caprolactone) triblock copolymers

The triblock copolymer based on poly(ε-caprolactone) (PCL) as hydrophobic part and poly(ethylene glycol) (PEG) as hydrophilic one was synthesized and characterized. Core-shell type nanoparticles of poly(ε-caprolactone)/poly(ethylene glycol)/poly(ε-caprolactone) (CEC) block copolymer were prepared by a dialysis technique. According to the amphiphilic characters, CEC block copolymer can self-associate at certain concentration and their critical association concentration (CAC) was determined by fluorescence probe technique. CAC value of the CEC-2 block copolymer was evaluated as 0.0030 g/l. CAC values of CEC block copolymer decreased with the increase of PCL chain length, i.e. the shorter the PCL chain length, the higher the CAC values. From the observation of transmission electron microscopy (TEM), the morphologies of CEC-2 core-shell type nanoparticles were spherical shapes. Particle size of CEC-2 nanoparticles was 32.3±17.3 nm as a monomodal and narrow distribution. Particle size, drug loading, and drug release rate of CEC-2 nanoparticles were changed by the initial solvents and the molecular weight of CEC. The degradation behavior of CEC-2 nanoparticles was observed by 1H NMR spectroscopy. It was suggested that clonazepam (CNZ) release kinetics were dominantly governed by diffusion mechanism.

Self-Association of Cholesterol-End-Capped Poly(sodium 2-(acrylamido)-2-methylpropanesulfonate) in Aqueous Solution

Poly(2-(acrylamido)-2-methylpropanesulfonic acid) sodium salt end-capped with a cholesterol moiety (Chol-PAMPS) was prepared by free radical polymerization of 2-(acrylamido)-2-methylpropanesulfonic acid (AMPS) initiated by a cholesterol-substituted azo compound, 4,4‘-azobis(4-cyano-1-cholesteryl)pentanoate, and the associative behavior of Chol-PAMPS in aqueous solution was studied by 1H NMR, size exclusion chromatography (SEC), static light scattering (SLS), quasielastic light scattering (QELS), and fluorescence probe techniques. For a reference polymer (AIBN−PAMPS), polyAMPS of a similar molecular weight with that of Chol-PAMPS was prepared in the presence of 2,2‘-azobis(2-methylpropionitrile) as an initiator. The degree of polymerization (DP) of Chol-PAMPS was estimated to be about 70 from a 1H NMR spectrum (in DMSO-d6) by assuming disproportionation for the termination. This DP value agreed fairly well with that estimated by SEC in water/acetonitrile using sodium poly(styrenesulfonate)s as standards. QELS indicated that Chol-PAMPS formed multipolymer aggregates at polymer concentrations (CP) higher than 0.5 g/L in 0.1 M NaCl. Fluorescence emission and excitation spectra for pyrene probes solubilized in the aggregates of Chol-PAMPS suggested the presence of a critical micelle concentration (cmc) around CP ≈ 0.6 g/L in water. Above this CP, the micellelike aggregates coexist with unimers over a wide range of CP. In the CP regime of 1.0−5.0 g/L, hydrodynamic radii for the aggregates were practically constant at about 50 nm. However, when CP was increased beyond this CP regime, the size increased considerably with CP. Given DP ≈ 70 for Chol-PAMPS, these sizes for the aggregates are obviously too large for a single spherical micelle with cholesterol groups in the core and extended polyAMPS chains in the corona. The structures of these multipolymer aggregates remain to be an open question, but these results are explained by considering that some polymer chains possess cholesterol groups at both chain ends and spherical micelles are bridged by these polymer chains.

Preparation and properties of chitosan-poly(N-isopropylacrylamide) semi-IPN hydrogels

Chitosan (CS), CS-poly(N-isopropylacrylamide)(PNIPAM) and their dyed (pyrene) hydrogels were prepared using glutaraldehyde (Glu) as a crosslinker. The gelation rate, swelling behaviors in ethanol/water mixtures, electricity-induced contraction and thermoresponse of the gels were investigated using fluorescence probe technique. Results showed that CS/Glu, and PNIPAM-containing CS/Glu gels exhibited similar properties in all aspects examined, except that the transparence of the CS-PNIPAM/Glu gel is very dependent upon the temperature. The CS-PNIPAM/Glu gel is transparent below 30°C, whereas opaque above 32°C. It is expected that this observation may be useful for the design and preparation of new kinds of hydrogel devices. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 474–481, 2000

Preparation and Characterization of pH-Responsive Polymeric Micelles for the Delivery of Photosensitizing Anticancer Drugs

pH‐responsive polymeric micelles (PM) consisting of random copolymers of N‐isopropylacrylamide (NIPA), methacrylic acid (MAA), and octadecyl acrylate (ODA) were prepared and characterized. The critical aggregation concentration, as determined by a fluorescence probe technique, was approximately 10 mg/L in water and phosphate‐buffered saline. Phase transition pH was estimated at 5.7. The decrease in pH was accompanied by the destruction of hydrophobic clusters. Micelle size was dependent on temperature and the nature of the aqueous medium. The micelles were successfully loaded with a substantial amount of a photoactive anticancer drug, namely, aluminum chloride phthalocyanine (AlClPc). pH‐responsive PM loaded with AlClPc were found to exhibit higher cytotoxicity against EMT‐6 mouse mammary cells in vitro than control Cremophor EL formulation. These results show the potential of poly(NIPA‐co‐MAA‐co‐ODA) for in vivo administration of water‐insoluble, photosensitizing anticancer drugs. © 2000 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 89: 52–62, 2000

A Study on Organized Assemblies in the Aqueous Systems of Alkylammonium Chlorides

Various types of organized assemblies, including micelle, planar multi-bilayer, bent multi-bilayer, fingerprint-like multi-bilayer, and multilamellar vesicles, were found in the aqueous system prepared by only one simple surfactant—alkylammonium chloride with a hydrocarbon chain length of 10 or 12. Electron microscopic images of the assemblies are provided. The properties of the system were characterized by DSC, fluorescence, and absorption probing techniques. It was found that the structure and shape of molecular assemblies in this system can be adjusted by very simple physico-chemical measures, such as pH adjustment and alcohol or salt addition. The mechanisms of formation and transformation of various molecular assemblies were discussed based on the mixing effect of the cationic amphiphile and the nonionic amphiphile which is only a hydrolysis product of the former.

Mixed micelles of triton X100: interaction, composition, stability and micro-environmental properties of the aggregates

Micellization of aqueous binary mixtures of triton X100 (TX100) in the presence of sodium dodecyl sulphate (SDS), cetyltrimethylammonium bromide (CTAB), and octaoxyethylene monodecyl ether (C12E8) has been investigated by the fluorescence probe technique. The critical micelle concentration values of the three binary combinations (TX100—SDS, TX100—CTAB and TX100—C12E8) in the whole range of compositions, obtained by using the pyrene 1:3 ratio method, were analysed in the light of the conventional regular solution theory for mixed micelles, as well as according to the formulation recently proposed by Maeda (1995, J. Colloid Interface Sci., 172, 98). This last theoretical approach was found to be very appropriate for describing the nature of the interactions involved in the formation and stability of the mixed micelles of TX100. Studies on the micropolarity of the mixed aggregates, as sensed by the probe pyrene, indicated that the incorporation of cosurfactant in the TX100 micelle induces the formation of mixed micelles with a more dehydrated structure. Data obtained from the polarized fluorescence measurements of diphenylbutadiene solubilized in the micellar phase, which were analysed according to the ‘wobling-in-cone’ model, showed the appearance of a less ordered micro-environment around the probe as cosurfactant proportion in the mixed micelle increased. The results obtained indicate that SDS is the cosurfactant which exerts a more pronounced effect on the micro-environment properties of mixed micelles.

Amphiphilic association of ibuprofen and two nonionic cellulose derivatives in aqueous solution

The aqueous interaction of the sodium salt of ibuprofen with the cellulose ethers ethyl hydroxyethyl cellulose, EHEC, and hydroxypropyl methyl cellulose, HPMC, has been investigated in the concentration range 0–500 mM ibuprofen and 0.1–1% (w/w) polymer, by cloud point, capillary viscometry, equilibrium dialysis, and fluorescence probe techniques. Ibuprofen forms micelles in pure water, with the critical micelle concentration, cmc, at 180 mM. A combination of time-resolved and static fluorescence quenching shows that micelle-like ibuprofen aggregates are formed in the solution. The average aggregation number of pure ibuprofen micelles in water is about 40. In the presence of EHEC or HPMC the aggregation numbers decrease. The interaction of ibuprofen with cellulose ethers is similar to the normally accepted model for polymer–surfactant interaction, although more complex. Ibuprofen adsorbs to the polymer in the form of mixed polymer–drug micelles, noncooperatively up to cmc and cooperatively when cmc is passed. The interaction starts below 50 mM ibuprofen as monitored by the fluorescent probes pyrene and 1,3-di(1-pyrenyl)-propane, P3P, with a maximum in microviscosity below cmc, corresponding to polymer-dense mixed micelles. The study illustrates the importance of a precise apprehension of the aggregation behavior as a background for transport studies in drug–polymer systems.

Microstructures formed in aqueous solutions of a hydrophobically modified nonionic cellulose derivative and sodium dodecyl sulfate: a fluorescence probe investigation

The association behavior of hydrophobically modified ethyl hydroxyethyl cellulose (HM-EHEC) and its interaction with the anionic surfactant sodium dodecyl sulfate (SDS) has been studied in the dilute concentration regime. Steady-state fluorescence probe techniques have been utilized to obtain microstructural information of the system properties and combined with macroscopic bulk information from equilibrium dialysis experiments in order to determine binding isotherms of SDS to HM-EHEC. HM-EHEC was found to self-associate and form polymeric micelles in semi-dilute aqueous solutions. c ∗ for the self-association process was determined to be approximately 0.4%. The microviscosity of the polymeric micelles is much higher, and the micropolarity slightly higher, than that of ordinary SDS micelles. The onset of interaction between HM-EHEC and SDS was evidenced by a simultaneous strong increase in microviscosity and decrease in micropolarity upon successive addition of SDS. There is a minor, noncooperative SDS binding to the HM-EHEC starting from low concentrations of SDS (<5 mM) followed by a highly cooperative binding region at SDS concentrations ≥5 mM. The polymer–surfactant aggregates are rigid and hydrophobic with a maximum in microviscosity in the noncooperative binding region at a very low degree of SDS-adsorption.

Stereodynamics of the vibrational channel O(1D)+H2O→OH(v′=2)+OH

The state-selected differential cross section (DCS) and rotational angular momentum polarization for the reaction O(1D)+H2O→OH+OH have been measured by utilizing the polarized Doppler-resolved laser-induced fluorescence probing technique. Stereodynamics of the reaction channel forming the newly formed OH in the specific vibrational level v′=2 is discussed on the basis of the vector properties. A nearly isotropic DCS for the product OH(2Π3/2, v′=2, j′=5.5) most probably indicates that the reaction is dominated by an insertion mechanism involving a collisional HOOH complex with a lifetime comparable to its rotational period. The extremely asymmetrical energy partitioning between the two OH fragments, therefore, suggests that the redistribution of the available energy does not occur on a time scale comparable to the rotational period of the complex. Furthermore, it has been found that the product rotational angular momentum vector j′ is predominantly perpendicular to the collision plane spanned by k and k′ (the relative velocity vectors of the reactants and products, respectively) both for the forward- and backward-scattered products. It suggests that the initially excited bending motion of the H–O–O moiety in the collisional HOOH complex primarily contributes to the product rotation.

Study of the Effect of Solubilized Gases on the Properties of Microemulsion Droplets

The effect of dissolved gas (nitrogen, argon) on the properties of the droplets in water-in-oil and oil-in-water microemulsions (surfactant aggregation number, microviscosity, and micropolarity) has been investigated by means of time-resolved fluorescence quenching and spectrofluorometry. This study extends a similar one on aqueous micellar solutions (R. G. Alargovaet al., Langmuir14, 1575, 1998). The selected microemulsions were characterized by droplets of fairly large size and high volume fraction, in order to minimize the effect of the curvature of the surfactant layer and maximize the amount of gas that can be solubilized in the system. Within the experimental error, the investigated properties (surfactant aggregation number, intradroplet quenching rate constant which is related to the droplet microviscosity, and fluorescent probe lifetime and micropolarity) were found to be independent on whether the system was degassed, nitrogen-saturated, or argon-saturated, in the temperature range between 10 and 35°C. The results confirm the conclusion reached in the above study; i.e., the effect of solubilized gases on the hydrophobic interaction which controls the formation of surfactant assemblies is extremely small and well below the sensitivity of the fluorescence probing techniques used in this investigation.

Effects of temperature on diblock copolymer micelle composed of poly( γ-benzyl L-glutamate) and poly( N-isopropylacrylamide)

Diblock copolymers composed of poly( γ-benzyl L-glutamate) and poly( N-isopropylacrylamide) (PNIPAAm) (abbreviated as GN) were prepared by the ring-opening polymerization of γ-benzyl L-glutamate N-carboxy anhydride (BLG-NCA) using amine-terminated PNIPAAm as a polymeric initiator. Polymeric micelles consisting of PBLG as the hydrophobic inner core and PNIPAAm as the hydrophilic outer shell were prepared by diafiltration method. Their critical micelle concentrations (cmc) were determined by fluorescent probe techniques with pyrene as a hydrophobic probe. The cmc of the polymeric micelle with the thermosensitive outer shell is less influenced by temperature than the ordinary polymeric micelle consisting of PBLG as the same innercore and poly(ethylene oxide) (PEO) as the hydrophilic outer shell (abbreviated as GE). Fluorescence results were used to estimate the thermodynamic data of micelle formation, such as the standard Gibbs energies (Δ G 0), the standard enthalpies (Δ H 0), and the standard entropies (Δ S 0) of micellization. For the GN/water system, Δ S 0 was found to be positive and so was favorable to micelle formation whereas Δ G 0, Δ H 0, and Δ S 0 for the GE/water system were found to be negative. The partition constant of pyrene in these micelles has a value of the order of 5 and inflection of the change of that for GN with temperature was found around the LCST of PNIPAAm.

Self-Assembling Nanospheres of Hydrophobized Pullulans in Water

In this report, we have prepared self-assembling nanospheres of hydrophobized pullulans. Pullulan acetate as a hydrophobized pullulan was synthesized by acetylation of pullulan and characterized by Fourier transform infrared (FTIR) measurement. From the results of photon correlation spectroscopy (PCS), hydrophobized pullulans could be self-assembled in water as nanospherical aggregates, and their number-average particle size was 74.3 ± 38.2 nm with a unimodal distribution. Also, morphological studies observed by transmission electron microscopy (TEM) showed that self-assembly of hydrophobized pullulans results in nice spherical shapes with a size range of about 50–100 nm, which was in accordance with PCS measurements. Their size and morphology have acceptable properties for intravenous injectable drug-targeting carriers. The fluorescence probe technique was used for self-association of hydrophobized pullulans in water using pyrene as a hydrophobic probe. From the fluorescence measurement, the fluorescence intensity of pyrene increased with increasing concentration of hydrophobized pullulans, which indicates self-assembly formation of hydrophobized pullulans in water. Also, in the fluorescence excitation spectrum, a red shift was observed with increasing concentration of hydrophobized pullulans. These results also revealed that hydrophobized pullulans could be self-assembled in water, and from the plot of I337/I334 versus log c of hydrophobized pullulans, the critical association concentration was 0.0022 g/l, which was considerably lower than that of low molecular weight surfactants or poloxamer. A drug loading study was performed using clonazepam (CNZ) as a hydrophobic model drug. We observed that the higher the feeding amount of drug was, the more the drug loading contents were, the lower the drug loading efficiency was, and the larger the particle size was. CNZ was released from nanospheres via pseudo-zero-order kinetics, and the increased drug loading contents led to slower release of the drug.

Relative Activity of Possible Initiating Species Produced from Photolysis of Tetraphenyl and Triphenylbutyl Borates As Measured by Fluorescence Probe Techniques

Fluorescence probe techniques (FPT) have been used to obtain curing profiles for the polymerization of a model monomer, triethylene glycol diacrylate (TEGDA). A number of new chromophore ammonium salt triphenylbutyl and tetraphenylborates differing only in the structure of the ammonium salt moiety have been used as photoinitiators. The borates were chosen for study so that a comparison of their initiation efficiency would reveal information about the relative activity of possible initiating species produced upon borate photodecomposition. The results support our previous postulate that an α-aminoalkyl radical formed immediately after unimolecular decomposition from the tetraphenylborates is the most effective initiating species and that α-aminoalkyl radicals significantly increase the photoinitiator efficiency of triphenylbutylborates as well. The importance of other radicals to the initiation step is also discussed.

Micropolarity and Order in the Reverse Micelles of L62 and L64 Pluronic Copolymers, As Studied by Molecular Probe Techniques

The reverse micelles of triblock copolymers poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) EO6PO36EO6 (Pluronic L62) and EO13PO30EO13 (Pluronic L64) in ternary (copolymer/o-xylene/water) and binary (copolymer/water) systems with different water contents were evidenced and investigated by fluorescence, absorption, and spin probe techniques. The spectral parameters of the polarity sensitive probes, 1-anilinonaphthalene-8-sulfonic acid (ANS), dansylhexadecylamine (Dansyl), pyrenesulfonic acid (PSA), 4-nitropyridine N-oxide (NP) and 4-(N,N‘-dimethyl-N-alkyl)ammonium 2,2‘,6,6‘-tetramethylpiperidine-1-oxyl iodide (CAT n), were related to the local hydration and polarity by comparison with a series of poly(oxyethylene)/water (TEG/water) calibration mixtures. The data were concordant and complementary, resulting in polarity profiles of the core for all systems and the relative radial positioning of the probes. The order of decreasing hydrophobic character found was Dansyl > NP > CAT 16 > CAT 11 ∼ ANS > CAT 8 > PSA > CAT 4 > CAT 1. A linear relationship was found between the RA (the intensity ratio of two absorption vibronic bands) of PSA in ethanol/water mixtures and Kosower's Z parameter (Z = −29.0RA + 177.83). Thus, by means of the calibration mixtures, converting different spectral parameters of the mentioned probes, the local polarity values were expressed in terms of Z values. The role of water as a prerequisite for micellization was evidenced and so was the minimum quantity of water required in the ternary systems (W = 0.2 for L64 and W = 0.4 for L62). Regarding the water distribution, a more advanced segregation of water is observed in the ternary systems as compared to the binary ones, pointing to the role played by the solvent in this process. Evidence was found for a considerable solvation of the poly(propylene oxide) block with xylene, leading to a looser packing in the corona and in the poly(ethylene oxide) core. In the case of ternary systems, the ordering of the polymer chains in the micelles, measured with a series of x-doxylstearic acid spin probes, indicates the progress of micellar organization with increasing water content, the order increasing and extending further from the polar core and the corona becoming less penetrable. In the corresponding binary systems, the polymer chain rotation is “frozen” at room temperature (295 K) and even at 320 K. The structural characteristics of L62 and L64 ternary systems are rather similar, a conclusion suggested especially by the information the polar probes supplied. There are differences in the microenvironment of more hydrophobic probes, which sense a higher hydrophobicity in the case of L62, the increase of microviscosity being also more marked in the L62 system.

Fluorescence Probe Techniques (FPT) for Measuring the Relative Efficiencies of Free-Radical Photoinitiators

A new method for determining the relative efficiencies of free-radical photoinitiators is reported. Called the fluorescence probe technique (FPT), the method has been used to determine the relative initiation efficiencies of several commercial photoinitiators and new phenyl glyoxylate derivatives in the photopolymerization of a model monomer, triethylene glycol diacrylate. The reactivity of each initiator was measured in reference to that of a standard commercial initiator, 2,2-dimethoxy-2-phenylacetophenone, Irgacure 651. Efficiencies differ widely among the acetophenone derivatives studied, and the phenylglyoxylate initiators are somewhat less reactive than the standard.

Microviscosity in dilute aqueous solutions of SDS and non-ionic cellulose derivatives of different hydrophobicity: fluorescence probe investigations

The microviscosity in mixed micelles formed in dilute aqueous solutions of sodium dodecyl sulphate (SDS) and a set of non-ionic cellulose ethers of different hydrophobicity has been determined by means of steady-state fluorescence probe techniques. Two hydrophobic probes have been applied in this investigation: 1,3-di(1-pyrenyl)propane (P3P) and perylene. Reference measurements of microviscosity have also been performed on SDS solutions including the uncharged polymers poly(ethyleneoxide) (PEO) or poly(vinylpyrrolidone) (PVP). All compositions investigated showed qualitatively the same general behaviour with an abrupt increase in microviscosity at the critical surfactant concentration where the polymer-surfactant interaction starts ( c 1) followed by a maximum and an asymptotically declining region as the surfactant concentration was increased further. Comparison with a recent investigation of a specific ethyl(hydroxyethyl)cellulose (EHEC fraction CST-103)/ SDS/water system (Evertsson & Nilsson (1997) Macromolecules, 30, 2377) revealed that the maximum in microviscosity generally corresponds to a low degree of SDS adsorption (≈ 0.5 mmol of SDS per gram of polymer) and consequently to a high polymer content of the mixed micelles formed in the type of systems studied herein. The hydrophobicity of the cellulose derivatives was found to correlate to the amplitude of the overall microviscosity pattern for the mixed micelles, i.e. an increased polymer hydrophobicity gave an increased rigidity of the polymersurfactant aggregates. An approximately exponential relation was demonstrated between the maxima in microviscosity of the different mixed micelles and the surface activities of the corresponding cellulose derivatives. All polymer/surfactant combinations investigated gave aggregates with a higher rigidity than ordinary SDS micelles. The microviscosity of the mixed micelles of the cellulose derivatives and SDS formed close to c 1 increased as the temperature rose from 20 to 50 °C. This effect was attributed to an increased hydrophobicity of the cellulose ethers upon temperature elevation, hence giving rise to further close-packing of the aggregate structures.

An AB block copolymer of oligo(methyl methacrylate) and poly(acrylic acid) for micellar delivery of hydrophobic drugs

An AB block copolymer of oligo(methyl methacrylate) (oMMA) and poly(acrylic acid) (PAAc) has been synthesized. The block copolymer forms micelles in an aqueous medium, as confirmed by a fluorescence probe technique using pyrene. Doxorubicin hydrochloride was incorporated into the micelle and the release profile of doxorubicin hydrochloride was investigated. Slow and prolonged release of doxorubicin hydrochloride from the micelle was observed. The AB block copolymer micelle can be useful for prolonged mucosal drug delivery of hydrophobic drugs.

Structural Determination and Interior Polarity of Self-Aggregates Prepared from Deoxycholic Acid-Modified Chitosan in Water

Hydrophobically modified chitosan derivatives containing 0.6−5.1 deoxycholic acid groups per 100 anhydroglucose units of chitosan were synthesized by an EDC-mediated coupling reaction. Self-aggregates of the chitosan derivatives in aqueous media were formed by sonication with a probe-type sonifier. The mean diameter of self-aggregates determined by dynamic light scattering decreased slightly with an increasing degree of substitution (DS) by hydrophobic groups. Photophysical and photochemical characteristics of self-aggregates were examined by fluorescence probe techniques. Measurement of the binding equilibrium constant (Kv) for pyrene and lifetime (τ) for 1,6-diphenyl-1,3,5-hexatriene (DPH) showed that the interior of self-aggregates became nonpolar as the DS was increased. Microviscosity of the interior of self-aggregates determined by measuring an anisotropy value for DPH was not significantly affected by the DS of hydrophobic groups. The aggregation number of deoxycholic acid groups per one hydrophobi...