title: Encapsulation of a hydrophobic drug into a polymer-micelle core explored with synchrotron SAXS.
abstract: Synchrotron small-angle X-ray scattering (SAXS) at the SPring-8 40B2 and 45XU beamlines was carried out on aqueous solutions of (PEG-P(Asp(Bzl))): partially benzyl-esterified poly(ethylene glycol)-block-poly(aspartic acid) with LE540 loaded up to 8.3 wt %, where LE540 is a very hydrophobic retinoid antagonist drug. The scattering profiles showed characteristic features for core-shell spherical micelles, confirming that P(Asp(Bzl)) forms a hydrophobic core and PEG forms a hydrophilic shell. Before the addition of LE540, a diffraction peak was observed around q = 4 nm(-1), where q is the magnitude of the scattering vector. This peak can be attributed to ordering between alpha-helices made of P(Asp(Bzl)), the so-called nonspecific hexatic arrangement. The P(Asp(Bzl)) helices disappeared as LE540 was added. This result can be interpreted by assuming a uniform distribution of LE540 in the core. By use of a core-shell spherical micelle model, the SAXS data could be well fitted for all of the samples. The analysis indicated that the core radius increases sigmoidally from 5.9 to 6.9 nm upon addition of LE540 whereas the shell radius stayed at 12.5-12.8 nm. The aggregation number that is the average number of PEG-P(Asp(Bzl))'s consisting of one micelle slightly increased from 145 to 182.
authors.affiliation: Department of Chemistry and Biochemistry, The University of Kitakyushu, 1-1 Hibikino, Kitakyushu 808-0135, Japan. akiba@env.kitakyu-u.ac.jp
authors.forename: Isamu
authors.initials: I
authors.lastname: Akiba
authors.forename: Naotaka
authors.initials: N
authors.lastname: Terada
authors.forename: Satoshi
authors.initials: S
authors.lastname: Hashida
authors.forename: Kazuo
authors.initials: K
authors.lastname: Sakurai
authors.forename: Taku
authors.initials: T
authors.lastname: Sato
authors.forename: Kouichi
authors.initials: K
authors.lastname: Shiraishi
authors.forename: Masayuki
authors.initials: M
authors.lastname: Yokoyama
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Masunaga
authors.forename: Hiroki
authors.initials: H
authors.lastname: Ogawa
authors.forename: Kazuki
authors.initials: K
authors.lastname: Ito
authors.forename: Naoto
authors.initials: N
authors.lastname: Yagi
mesh_terms: D003984:Dibenzazepines / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D008823:Micelles; D015394:Molecular Structure; D011092:Polyethylene Glycols / Q000737:chemistry*; D053838:Scattering, Small Angle; D013499:Surface Properties; D017356:Synchrotrons; D014961:X-Ray Diffraction
chemical_list: D003984:Dibenzazepines; C104183:LE 540; D008823:Micelles; C493635:polyethylene glycol-block-polyaspartic acid; D011092:Polyethylene Glycols