Iwao Satake

Absorption and fluorescence studies of the interaction of pyrene with β-cyclodextrin in aqueous surfactant solutions

Abstract The system pyrene-cyclodextrin-sodium dodecyl sulfate (SDS) in aqueous solution was studied as a function of the concentration of SDS. The behavior of absorption and fluorescence spectra of pyrene is explained in terms of complex formation with β-cyclodextrin and SDS below the critical micelle concentration and the formation of mixed micelles containing α- or β-cyclodextrin above it.

Conformational change of poly(L-lysine) and poly(L-ornithine) and cooperative binding of sodium alkanesulfonate surfactants with different chain length

Conformations of poly(L-lysine) (PLL) and poly(L-ornithine) (PLO) were examined in aqueous solutions of sodium alkanesulfontates (CnSO3Na, n=9, 10, 11, 12) in the presence of 0.02 M NaCl by circular dichroism (CD) spectroscopy. These surfactants induce theβ-structure for PLL and theα-helix for PLO. The binding of surfactants on the polypeptides was measured potentiometrically with a surfactant ion electrode and was found to be highly cooperative. The cooperativity increases with increasing chain length of surfactant. The behavior accompanying the surfactant binding and the conformational change indicated that the conformational change requires a certain amount of bound surfactants in the case of C9SO3Na and starts immediately on binding of surfactant in the case of C12SO3Na. The clustering of bound surfactants due to the cooperative binding as well as neutralization of polypeptides contributes to their conformational change. A slow conformational change of PLO was found in the time scale of hours, sometimes days, for C9- and C10SO3Na at low concentrations, but the binding process reached the equilibrium quickly. This slow mode might occur due to the slow interaction between surfactant/polypeptide complexes.

Spectroscopy of rhodamine 6G solubilized in complexes of anionic polymers with cationic surfactant

Abstract Absorption and emission spectra of rhodamine 6G (R6G) are reported in mixed solutions of dodecyltrimethylammonium bromide (DTAB) with various polyelectrolytes, including the sodium salts of poly(acrylic acid) (PAA), poly(methacrylic acid) (PMA), poly(styrenesulfonic acid) (PSS), polygalacturonic acid (pectate), and the alternating copolymers of maleic acid with ethylene (PMA-E) and styrene (PMA-St). In the systems of PAA, PMA, PMA-E and PMA-St, in the absence of surfactant, the R6G absorption spectrum has a strong dimer band and exhibits remarkable quenching of the emission spectrum indicating self-association of R6G in the polyion domain. Upon addition of DTAB, the dimer band disappears, the monomer band increases and the emission intensity recovers at a longer wavelength than that for the monomer band in aqueous solution. These observations are explained by the self-association of R6G in the polyion solutions, followed by the solubilization of R6G in the monomeric form in polyion-DTA complexes. In the case of PSS a red-shift of the R6G monomer band is observed in the absorption spectrum of R6G in solution of PSS alone, and the dimer band is absent. In this case DTAB addition does not affect the monomer band position and induces only a small dimer band maximum at high DTAB concentration, indicating territorial site-binding of R6G and DTA. In the pectate system, only minor changes in absorption and emission spectra are observed in the solution of pectate alone, and addition of DTAB leads to full recovery of the free solution spectra, indicating a weak interaction of R6G with pectate. These results are discussed in terms of different competitive, cooperative binding processes of R6G and DTAB by the various polyions.

Adsolubilization equilibrium of rhodamine B by zeolite/surfactant complexes

Adsolubilization of the cationic dye rhodamine B (RB) into the adsorption layers of two cationic surfactants, dodecyltrimethylammonium bromide (DTAB) and tetradecyltrimethylammonium bromide (TTAB), on a high silica mordenite (HSZ-3) and a P-type zeolite (ZP) has been examined quantitatively. A critical quantity of adsorbed surfactant was required for the adsolubilization of RB by the HSZ-3/surfactant complexes, while ZP/TTAB complex adsolubilized RB even at a very small quantity of adsorbed TTAB. The adsolubilization constant and the maximum capacity were determined based on Langmuir type equation. The difference in adsolubilization mode between HSZ-3/surfactant and ZP/surfactant complexes was discussed in relation to the aggregation mode of the cationic surfactant on the zeolites.

Conformation of Poly(L-lysine) and Poly(L-ornithine) in α, ω-Type Surfactant Solutions

Circular dichroism spectra of poly(L-ornithine) and poly(L-lysine) were measured in disodium α, ω-alkanedisulfate [Na2C n H2 n (SO4)2( n = 8,10, 12,16) (RDS)] solutions in the presence and absence of NaCl at various tempera tures. The 1,16-RDS induced an α-helix in poly(L-ornithine) and a β-sheet in poly(L-lysine) at 30°C, while 1,10- and 1,8-RDS induced no conformational change in either polypeptide even at a surfactant concentration where turbid ity appears. Although 1,12-RDS induced no conformational change in poly(L- ornithine), it does induce α-helix, β-sheet or stepwise transition from coil to β-sheet and then to α-helix with increasing 1,12-RDS concentration, depending on the temperature and concentration of added NaCl. The plots of α-helix con tent against temperature at various concentrations of 1,12-RDS are quali tatively consistent with the dependence of α-helix content on the size growth of surfactant cluster bound to polypeptide.