Contrary hydration behavior of N-isopropylacrylamide to its polymer, P(NIPAm), with a lower critical solution temperature.

The number of hydrated water molecules per N-isopropylacrylamide in homogeneous aqueous solution was determined to be a constant with a value of 5-6 below and above the lower critical solution temperature, LCST (32 degrees C), of its polymer, poly(N-isopropylacrylamide), by high-frequency dielectric relaxation techniques.

Hydration and dynamic behavior of poly(N-isopropylacrylamide)s in aqueous solution: a sharp phase transition at the lower critical solution temperature.

The number of hydrated water molecules per poly(N-isopropylacrylamide) monomer unit in homogeneous aqueous solution was determined to be 11 exactly and anew below the lower critical solution temperature of 32 degrees C employing high-frequency dielectric relaxation techniques.

Reversible micelle-vesicle conversion of oleyldimethylamine oxide by pH changes.

A preliminary study on the reversible micelle-vesicle conversion of oleyldimethylamine oxide [Kawasaki, H. et al. J. Phys. Chem. B. 2002, 106, 1524 ] is extended in the present study. In the presence of 0.01 M NaCl at a surfactant concentration of 0.05 M, a micelle-to-vesicle conversion with increasing degree of ionization alpha takes place in the following sequence: growth of fibrous micelle (alpha < 0.2), a fused network (alpha approximately 0.3), fibrous micelles + (perforated) vesicles (alpha = 0.4), and vesicles + lamellae (alpha = 0.5). Viscoelasticity correspondingly varies from the Maxwell-type behavior of the entangled network of fibrous micelles to the gel-like behavior of vesicle suspensions, via a fluid solution-like behavior of the fused network. This phase sequence is in contrast with the case of no added salt where no branching of micelles is observed, and long micelles and bilayers (vesicles + lamellae) coexist at alpha = 0.5. In water, a state of the lowest viscoelasticity occurs around alpha = 0.2 for both surfactant concentrations 0.05 and 0.15 M. Synergism between protonated and nonprotonated amine oxide headgroups is observed despite low ionic strengths. From the time course of the reversible micelle-vesicle conversion, vesicles seem to be formed from threadlike micelles within 25 h according to the shear moduli, while a longer conversion time is suggested by a flow property (viscosity). Shear thickening behavior is observed at alpha = 0.2 and 0.4 in 0.01 M NaCl but not in water.

Dielectric relaxation behavior of aqueous solutions of carbobetaines with varying intercharge distances.

The dielectric relaxation behavior of aqueous triethylammonioalkanoate (carbobetaine: Et(3)nCB) solutions was examined as a function of frequency from 1.00 x 10(6) to 2.00 x 10(10) Hz (6.28 x 10(6) to 1.26 x 10(11) rad s(-1) in angular frequency); number of intercharge methylene groups, n = 1, 3, 4, 5, and 10; and solute concentration, c. Two major relaxation modes, fast and slow, were found in all solutions examined. Et(3)nCB systems with n = 5 and 10 possessed another, medium, relaxation mode with relaxation time tau(Dh) at high c values (above the contact concentration of solutes) in addition to the fast and slow modes. The fast mode with a relaxation time, tau(w), of approximately 10 ps was attributed to the rotational motion of bulk water molecules. The slow mode with a relaxation time, tau, of 0.08-1 ns, depending on the n value, was attributed to the overall rotational motion of each carbobetaine in aqueous solution. The concentration normalized relaxation strength, Deltaepsilonc(-1), and tau value of the slow relaxation mode increased with increasing n. These findings were quantitatively explained on the basis of changes in the intercharge distance resulting in increased size and dipole moment of the carbobetaines. Above the contact concentration, collisions between solute molecules likely hindered their rotational motions, leading to an increase in tau. The middle relaxation mode found in longer Et(3)nCBs (n = 5 and 10) with a relaxation time, tau(Dh), of approximately 0.2 ns, more than 20 times as long as that of bulk water molecules, tau(w), was attributed to the dehydration of water molecules tightly bound to all Et(3)nCBs examined (including those with n < 5). This mode was not observed in the solutions of Et(3)nCBs with n < 5, since the tau values corresponding to overall rotation were close to or shorter than the tau(Dh) values.

Effects of micelle-to-vesicle transitions on the degree of counterion binding.

Effects of micelle-to-vesicle transitions on the degree of counterion binding (beta) were investigated on three systems. For the concentration-dependent micelle-to-vesicle transition in the didodecyldimethylammonium bromide (DDAB)/water system, in the region of coexistent micelles and vesicles, less than 3 mM, the beta values increased significantly with DDAB concentration: beta (0.07 mM)=0.35 and beta (3 mM)=0.93. In the coexistent region, activities of the bromide ion, a(Br), were almost independent of the DDAB concentration, suggesting the pseudo-phase nature of both micelles and vesicles. In the concentration-dependent vesicle-to-lamellar transition region above 5 mM, where multilamellar vesicles were prevailing, on the other hand, the beta values were only little affected by this transition. This suggests that the increase in the layer number of DDAB multilamellar vesicles scarcely affects the beta values. This was also supported by the fact that the destruction of multilamellar vesicles by ultrasonication did not change the beta values. These results strongly suggest that the inner and outer monolayers of DDAB multilamellar vesicles are characterized by similar beta values. The second system, cetyltrimethylammonium bromide (CTAB)/DDAB mixtures, showed composition-dependent transitions depending on the mole fraction of DDAB X(DDAB): spherical micelles (0rodlike micelles (0.2vesicles (0.6

Dielectric behavior of aqueous micellar solutions of betaine-type surfactants.

Dielectric behavior was examined for aqueous solutions of the betaine-type surfactants dodecyldimethylcarbobetaine (C(12)DCB), tetradecyldimethylcarbobetaine (C(14)DCB), cetyldimethylcarbobetaine (C(16)DCB), and oleyldimethylcarbobetaine (OleyDCB) as a function of frequency from 1.00 x 10(6) to 2.00 x 10(10) Hz (6.28 x 10(6) to 1.26 x 10(11) rad s(-1)) with changing surfactant concentration (c(D)). Rotational relaxation times (tau) of the zwitterionic headgroups of the surfactants in aqueous solutions of C(12)DCB and C(14)DCB, which form spherical micelles, are determined to be 0.26 and 0.30 ns, respectively. Values of tau for aqueous solutions of C(16)DCB and OleyDCB, which form threadlike micelles, are identical at 0.44 ns. The tau values of all micellar solutions are constant irrespective of c(D). The increase in tau with increasing alkyl chain length is assigned to an increase of molecular density at the micellar surface. The magnitude of the relaxation strength for the surfactant solutions increases in proportion to c(D) and is not so different from that of an aqueous solution of glycine betaine (GB), which has the same chemical structure as betaine-type surfactants with zwitterionic headgroups but never forms micelles. This finding suggests that the zwitterionic headgroup rotating on the micellar surface possesses a dipole moment with a magnitude essentially the same as that of GB in aqueous solutions.

Production of secretory immunoglobulin A against Shiga toxin-binding subunits in mice by mucosal immunization.

The toxicity of Shiga toxins (Stx) depends on the binding of their B subunits to carbohydrate ligands on host cells. The production of antibodies against B subunits, especially immunoglobulin A (IgA) secreted on the mucosal surface, should contribute to host defense. One of the major problems in attempts to produce IgA against Stx was the poor immunogenicity of B subunits. We were able to produce serum IgA as well as IgG against Stx1B in mice of the H-2d haplotype by means of intranasal immunization with recombinant B subunits of Stx (Stx1B) together with cholera toxin as a mucosal adjuvant. Secretory IgA (S-IgA) was detected in nasal washes but not in feces. We prepared chemically cross-linked Stx1B for use as an immunogen, and the formation of stable oligomers was revealed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and mass spectrometry. When the cross-linked Stx1B was used together with cholera toxin for the intranasal immunization of BALB/c mice, strong enhancement of the immune response was observed. The S-IgA titers in nasal washes were 16- to more than 64-fold higher than those in mice immunized with native Stx1B plus cholera toxin. Furthermore, fecal IgA was detectable when the cross-linked Stx1B was used. The use of cholera toxin was necessary for the induction of high titers of S-IgA in the nasal washes. However, the effect of cross-linking was dependent on the major histocompatibility complex haplotype; that is, no enhancement of IgA production was observed in C57BL/6 mice. The present results provide a practical means of producing IgA against Stx1B in BALB/c mice.

Restricted expression of shiga toxin binding sites on mucosal epithelium of mouse distal colon.

Shiga toxins (Stx) are some of the major virulence factors of enterohemorrhagic Escherichia coli strains such as serotype O157:H7. To explore how Stx might initially gain access to the bloodstream from sites of infection, frozen sections of mouse colon were immunohistochemically examined for binding sites for recombinant binding subunits (Stx1B). Binding sites were selectively expressed on the epithelium in the distal half of the mouse colon, whereas the proximal half did not exhibit any binding sites. In agreement with this observation, we also demonstrated the distal-part-restricted distribution of glycolipids that bind to Stx1B in the mouse colon. For comparison, the binding sites of several control lectins were also examined. Selective binding to the distal part of the colon was not seen with any other control lectins, including Griffonia simplicifolia lectin-I isolectin B4 (GS-I-B4), which shares alpha-galactose specificity with Stx1B. Partial overlapping of the specificities of Stx1B and GS-I-B4 was seen by assay with globotriose-conjugated multivalent ligands. The results indicate that Stx1B is stricter in the recognition of carbohydrate determinants than GS-I-B4 when examined with biological ligands.

Lack of Shiga-like toxin binding sites in germinal centres of mouse lymphoid tissues.

B cells in germinal centres are known to express carbohydrate antigen CD77 in human lymphoid tissues. The CD77 antigen is specifically recognized by Shiga-like toxins (SLTs) that are produced by enterohaemorrhagic Escherichia coli O157:H7. To determine whether the binding subunits of Shiga-like toxin-1 (SLT-1B) could have adverse effects on the murine immune system when used as an immunogen, we investigated whether SLT-1B could bind to germinal centres of mouse lymphoid tissues. Frozen sections of peripheral lymph nodes and Peyer's patches from immunized mice were tested for the presence of SLT-1B-binding sites by immunohistological methods. Germinal centres were not stained with SLT-1B, while they were intensely stained with peanut agglutinin (PNA), another marker of germinal centres. On the other hand, SLT-1B specifically bound to renal tubules and collecting ducts in frozen sections of mouse kidney. This is consistent with results from human tissues. We also demonstrated that B220/PNA double-positive populations in lymph nodes from immunized mice exhibited only marginal staining with SLT-1B. The present results suggest that SLTs would not impede germinal centre functions of the murine immune system.