Thermal stability of lysozyme Langmuir-Schaefer films by FTIR spectroscopy.

Fourier transform infrared spectroscopy has been applied to study the thermal stability of multilayer Langmuir-Schaefer (LS) films of lysozyme deposited on silicon substrates. The study has confirmed previous structural findings that the LS protein films have a high thermal stability that is extended in a lysozyme multilayer up to 200 degrees C. 2D infrared analysis has been used here to identify the correlated molecular species during thermal denaturation. Asynchronous 2D spectra have shown that the two components of water, fully and not fully hydrogen bonded, in the high-wavenumber range (2800-3600 cm-1) are negatively correlated with the amine stretching band at 3300 cm-1. On the grounds of the 2D spectra the FTIR spectra have been deconvoluted using three main components, two for water and one for the amine. This analysis has shown that, at the first drying stage, up to 100 degrees C, only the water that is not fully hydrogen bonded is removed. Moreover, the amine intensity band does not change up to 200 degrees C, the temperature at which the structural stability of the multilayer lysozyme films ceases.

Degradation and release profile of microcapsules made of poly[L-lactic acid-co-L-lysine(Z)].

Poly(L-lactic acid-co-L-lysine(Z)) with different Lys(Z) contents was synthesized by Sn(II) salt-catalyzed ring-opening copolymerization of 3(S)-benzyloxycarbonylaminobutyl-6(S)-methylmorpholine-2,5-dione with lactide. Microcapsules of the copolymers were prepared by solvent evaporation from w/o/w emulsion, and FITC-dextran release from the microcapsules was investigated. The FITC-dextran release was dependent on the composition and molecular weight of the copolymers. The release from the microcapsules containing Lys(Z) of 6.5 mol% was slowest among the present microcapsules, which is due to smooth surface and very small microcapsules included in a large microcapsule. On the other hand, the release from microcapsules containing Lys(Z) of 31 or 50 mol% became faster after several days of incubation. GPC measurement of the microcapsules revealed that the copolymers were degraded during the incubation. Cracks and pores were formed on the microcapsule wall. PLLA microcapsules having comparable molecular weight to the copolymers showed neither release acceleration nor degradation in short-time incubation. Therefore, the introduction of Lys(Z) units made PLLA susceptible to degradation to result in delayed acceleration of release.

Thermoresponsive release from poly(Glu(OMe))-block-poly(Sar) microcapsules with surface-grafting of poly(N-isopropylacrylamide).

Thermoresponsive microcapsules were prepared by grafting poly(N-isopropylacrylamide) (PNIPAAm) on the surface of polypeptide (poly(Glu(OMe))-block-poly(Sar) microcapsules. Naked poly(Glu(OMe)-block-poly(Sar) microcapsules were partly hydrolysed with NaOH to remove methyl groups and newly formed carboxyl groups were used to anchor polyallylamine having 4,4'-azobis(4-cyanovaleric acid) groups. Graft polymerization of N-isopropylacrylamide at the microcapsule surface was initiated by photo-cleavage of the azo groups. Microscopic examination showed that a homogeneous dense skin layer of PNIPAAm was formed on the surface of microcapsule at 40 degrees c, while the skin layer became loose when the temperature was lowered to 25 degrees C. Dextran release from the microcapsule was faster below the lower critical solution temperature (LCST) of PNIPAAm than that above it. When the temperature changed across the LCST, a reversible, thermoresponsive release from the microcapsule was observed. Notable, the transition of the release rate by changing the temperature occurs quickly in a narrow temperature range.

Amphiphilic poly(Ala)-b-poly(Sar) microspheres loaded with hydrophobic drug.

Amphiphilic block polypeptides, (Ala)m(Sar)n, were synthesized. Transmission electron microscopy showed that three kinds of block polypeptides, (Ala)42(Sar)21, (Ala)34(Sar)22, and (Ala)34(Sar)27, formed spherical aggregates in water. Dynamic light scattering measurement revealed that the average diameters of (Ala)42(Sar)21 and (Ala)34(Sar)22 aggregates were in the range of 80-90 nm, whilst that of (Ala)34(Sar)27 was about 30 nm. The polypeptides in aqueous solution took a beta-sheet structure, while they took an alpha-helical conformation in trifluoroethanol. These polypeptide aggregates took up 8-anilinonaphthalene-1-sulfonate (ANS), and the capacity of the aggregates for ANS decreased in the order of (Ala)42(Sar)21 > (Ala)34(Sar)22 > (Ala)34(Sar)27. Sumithion, which is a commercial agricultural insecticide, was also taken up by the polypeptide aggregates. When increasing amounts of Sumithion were introduced, (Ala)42(Sar)21 aggregates kept their shape, but (Ala)34(Sar)27 aggregate increased in size. These different behaviors of the polypeptide aggregates were discussed in terms of different structure of aggregates.