Biomedical subjects

Yoshikiyo Moroi

Publications and source records attributed to Yoshikiyo Moroi.

14 recordsLinked to original sources

PubMed2006

Pyrene fluorescence at air/sodium dodecyl sulfate solution interface.

The dependence of pyrene fluorescence spectra on the concentration of sodium dodecyl sulfate (SDS) was observed, where the solution was prepared from water saturated with pyrene. The values of the I(1)/I(3) ratio from the bulk solution and from the upper meniscus region in an optical cell were similar but decreased rapidly around the critical micelle concentration (cmc) of SDS, indicating that pyrene molecules preferred to be solubilized in the micelles having a lower dielectric constant. The fluorescence intensity of the excimer indicated the concentration of pyrene molecules at the air/solution interface or the surface activity of pyrene molecules. In addition, the intensity from the meniscus region is much larger than that from the bulk at the concentrations below the cmc, whereas there was no difference in the intensity between the bulk and the meniscus above 8 mmol dm(-3) of SDS. The analysis of the fluorescence intensity from the excimer strongly suggests the presence of molecular aggregates that are favorable to the pyrene molecules just like the micelles in the bulk, making them less movable.

Air↗

PubMed2005

Micellization of conjugated chenodeoxy- and ursodeoxycholates and solubilization of cholesterol into their micelles: comparison with other four conjugated bile salts species.

Micelle formations of sodium glyco- and taurochenodeoxycholate (NaGCDC and NaTCDC) and sodium glyco- and tauroursodeoxycholates (NaGUDC and NaTUDC) was studied at 308.2 K for their critical micelle concentrations at various NaCl concentrations by pyrene fluorescence probe, and the degree of counterion binding to micelle was determined using the Corrin-Harkins plots. The degree of counterion binding was found to be 0.37-0.38 for chenodeoxycholate conjugates, while the determination of the degree was quite difficult for ursodeoxycholate conjugates. The change of I1/I3 values on the fluorescence spectrum with the conjugate bile salt concentration suggested two steps for their bile salt aggregation. The first step is a commencement of smaller aggregates, the first cmc, and the second one is a starting of stable aggregates, the second cmc. The aggregation number was determined at 308.2 K and 0.15 M NaCl concentration by static light scattering: 16.3 and 11.9 for sodium NaGCDC and NaTCDC, and 7.9 and 7.1 for NaGUDC and NaTUDC, respectively. The solubilization of cholesterol into the bile salt micelles in the presence of coexisting cholesterol phase and the maximum additive concentration (MAC) of cholesterol was determined against the bile salt concentration. The standard Gibbs energy change for the solubilization was evaluated, where the micelles were regarded as a chemical species. The solubilization was stabilized in the order of NaGUDC approximately = NaTUDC < NaTC < NaGC < NaTCDC < NaGCDC < NaTDC < NaGDC, where the preceding results were taken into the order.

Bile Acids and Salts↗

PubMed2005

Examination of surface adsorption of sodium chloride and sodium dodecyl sulfate by surface potential measurement at the air/solution interface.

The surface potential (DeltaV) of the air/sodium chloride solution interface was measured by using an ionizing (241)Am electrode method at 298.2 K. The surface potential steeply increased from 0 up to 15 mV with increasing concentration, then gradually increased up to 20 mV between 1 and 10 mmol dm(-3), and finally stayed almost constant at 20 mV up to the concentration of 20 mmol dm(-3). This result means that sodium ions concentrate more just near the air/solution interface, whereas chloride ions concentrate more far below the interface above the bulk region of electroneutrality. The dipole moment was derived from the surface potential value, from which the width of the interfacial layer was estimated as a function of the magnitude of electric charge. As for the sodium dodecyl sulfate solution, on the other hand, the surface potential steeply decreased from 0 down to -80 mV with increasing concentration from 0 to 0.01 mmol dm(-3), then rapidly increased up to -50 mV between 0.1 and 3 mmol dm(-3), then linearly increased up to 0 mV with increasing concentration from 3 mmol dm(-3) up to the CMC, 8 mmol dm(-3), then quite rapidly decreased again down to -82 mV from the CMC to 10 mmol dm(-3), and finally stayed almost constant at -82 mV up to the concentration of 20 mmol dm(-3). The above variations of the surface potential cannot be elucidated by the conventional surface excess, and therefore, the new concept of surface adsorption was presented for a simple salt and a typical anionic surfactant.

Adsorption↗

PubMed2005

Evaporation from water-ethylene glycol liquid mixture.

Evaporation rates were determined for water-ethylene glycol liquid mixtures with different mole fractions, where the evaporation rate expressed as mg min(-1)/area was used because of the presence of two kinds of molecular species. The rate increased with increasing temperature and decreased with increasing mole fraction of ethylene glycol, almost obeying ideal mixing of the two components, although a small positive deviation was observed over the mole fraction from 0 to 0.5 of ethylene glycol at higher temperatures. The activation energy of evaporation was determined from the temperature dependence of the evaporation rate, where the energy was an apparent one because the composition of evaporated species was not determined. The activation energy increased with decreasing temperature and with increasing mole fraction of ethylene glycol, where the energy obeyed the ideal mixing at lower temperatures while it positively deviated at higher temperatures. The evaporation rates were examined by surface tension of the liquid mixture, but any definite relation between them was not found. Both the evaporation rate and the activation energy were found to be determined mainly by the mole fraction in the surface layer from which the evaporation takes place. Finally, the new concept of surface excess was presented, where the surfactant molecules were concentrated and formed a bimolecular layer at a certain distance beneath the air/solution interface.

Chemistry↗

PubMed2005

Micelle formation of N-(1,1-dihydroperfluorooctyl)- and N-(1,1-dihydroperfluorononyl)-N,N,N-trimethylammonium chlorides.

Micelle formation of N-(1,1-dihydroperfluorooctyl)-N,N,N- and N-(1,1-dihydroperfluorononyl)-N,N,N-trimethylammonium chloride was investigated by analyzing the concentration dependence of the electric conductivity and of the activity of the counterion (Cl(-)) of the solution. The three micellization parameters for ionic surfactants, the micellization constant K(n), the micelle aggregation number n, and the number of counterions per micelle m, were determined by combination of electric conductivity and counterion concentration. The present analysis employed two slopes of the plots of specific conductivity against surfactant concentration below and above the critical micelle concentration and the mass action model of micelle formation. The aggregation numbers thus obtained were relatively small, while the degrees of counterion binding to the micelle (m/n) were found to be quite large, much larger than expected from the small aggregation numbers. Thermodynamical parameters of the micellization were evaluated from the temperature dependence of the three parameters, and the micellization of the fluorinated surfactant was found to be enthalpy-driven. A CF(2) group in the perfluorocarbon chain was found to be 1.44 times larger in hydrophobicity for micellization than a CH(2) group in the hydrocarbon chain.

Journal Article↗

PubMed2004

Solubilization of n-alkylbenzenes in aggregates of sodium dodecyl sulfate and a cationic polymer of high charge density (II).

The solubilization property of the aggregate composed of sodium dodecyl sulfate (SDS) and a cationic polymer (polydiallyldimethylammonium chloride, PDADMAC) was investigated. From the binding isotherm, the increasing free SDS concentration (Cf) above the critical aggregation concentration (cac) was clearly confirmed and used to calculate the Gibbs free energy change of solubilization. The maximum additive concentration of the alkylbenzene solubilizates remained almost constant around their aqueous solubilities below the cac and then increased with increasing SDS concentration above the cac and with decreasing alkyl chain length of the solubilizates. Also, their solubility increased with increasing temperature over the concentration range of the surfactant examined. Because the monomeric DS- concentration in the aqueous phase (Cf) increased with the SDS concentration above the cac in the SDS/PDADMAC system, Cf was evaluated from the binding isotherm to calculate the change in the Gibbs energies of transfer of the solubilizates using the phase separation model. The Gibbs energy change for the solubilizates decreased with increasing temperature and increasing alkyl chain length. The decrease in the Gibbs energy per CH2 group (DeltaGCH2 degrees) was favored by an increase of temperature, and it was larger in magnitude than that for micelles of single-surfactant systems. From the values of DeltaH degrees and TDeltaS degrees, the solubilization of alkylbenzenes into SDS/PDADMAC was found to be entropy-driven.

Journal Article↗

PubMed2004

Investigation of the interaction between sodium dodecyl sulfate and cationic polymers.

Aggregation properties of sodium dodecyl sulfate (SDS) on a cationic hydroxyethyl cellulose, Polyquaternium-10 (PQ-10), of low charge density were studied by potentiometric and pyrene fluorescence methods and compared with those of poly(diallyldimethylammomium chloride) (PDADMAC) of high charge density. The critical aggregation concentration (cac) was measured with the potentiometric method and further confirmed with the fluorescence method. The former was found to be more accurate. The value of the cac for the SDS/PQ-10 system was measured at 100, 200, and 400 ppm polymer and at 288.2,298.2, and 308.2 K. They showed almost the same cac value, 0.04 mmol dm-3. The I1/I3 value of the pyrene fluorescence spectrum in the SDS/PQ-10 system at higher SDS concentration was smaller than that in SDS/PDADMAC solution and much larger than that of water. From the binding isotherm by the potentiometric method, the free DS- concentration (Cf) and the bound DS- concentration (Cb) could be evaluated with ease over the SDS concentration range above the cac. The aggregation number of DS- aggregates for both the above polymers was evaluated from the fluorescence quenching method using the values of Cf and Cb from the potentiometric method. Because Cf in the SDS/PQ-10 system above the cac did not maintain a constant value contrary to that in the SDS/PDADMAC system but increased quite a lot, Cb should not be regarded as [SDS] - cac above the cac. The aggregation number in the SDS/PQ-10 system increased almost linearly with increasing total concentration of SDS, while that in the SDS/PDADMAC system reached a plateau. With increasing temperature, the aggregation number of the SDS/PDADMAC system decreased more rapidly than that of the SDS/PQ-10 system.

Cations↗

PubMed2004

Solubilization study for aggregates of sodium dodecyl sulfate and cationic polymer of high charge density.

Interaction of sodium dodecyl sulfate (SDS) with a cationic polymer (polydiallyldimethylammonium chloride, PDADMAC) was investigated. The surface tension of SDS/PDADMAC solution ([PDADMAC]=100 ppm) decreased from 72 to ca. 40 mN m(-1) with increasing SDS concentration at 298.2 K, where the SDS concentration, 0.6 mmol dm(-3), at 40 mN m(-1) was less than cmc/10 of SDS. From the relatively high value of I1/I3, ca. 1.5, in the pyrene fluorescence spectrum, which is larger than the value in SDS micelles, the aggregation number is suggested to be lower than that of SDS micelles. The maximum additive concentration for n-alkylbenzenes as solubilizate increased with the increase in SDS concentration and with decreasing alkyl chain length of the solubilizates. The Gibbs energy changes for their solubilization from the phase separation model were almost the same as those from the mass action model for longer chain solubilizates, due to their smaller solubilized amounts in the micelles. The Gibbs energy change for the solubilization decreased with increasing alkyl chain length of the solubilizates. The Gibbs energy decrease per CH2 group (deltaG(CH2)0) was larger in magnitude than for micelles of single-surfactant systems, which was substantiated by the absorption spectrum change of the solubilizates.

Journal Article↗

PubMed2004

Study on water evaporation through 1-alkanol monolayers by the thermogravimetry method.

The influence of 1-alkanol monolayers on the rate of water evaporation has been studied by measuring water loss per unit time using thermogravimetry. The evaporation rate of water from the surface covered by an insoluble monolayer for each of four saturated 1-alkanols (C(13)OH, C(15)OH, C(17)OH, and C(19)OH) was measured as a function of temperature and alkyl chain length, where the monolayer was under equilibrium spreading pressure. The evaporation rate decreased with increasing alkyl chain length or increasing molecular interaction among 1-alkanol molecules in the insoluble monolayer. Using the Arrhenius equation, the activation energy for the water evaporation was calculated from the temperature dependence of the evaporation rate, which showed that the activation energy decreased with increasing temperature. On the other hand, the activation energy increased with increasing alkyl chain length, which indicates that the activation energy includes the energy to cross the insoluble monolayer at the air/water interface. This energy increased almost linearly with alkyl chain length, when the length is longer than a dodecyl group. This means that water molecules need more energy to escape from the liquid to the gaseous phase across a membrane of longer 1-alkanols, which becomes more evident at lower temperatures. The temperature dependence of the activation energy was slightly larger for longer 1-alkanols than for shorter ones.

Alcohols↗

PubMed2003

Micelle formation of sodium chenodeoxycholate and solubilization into the micelles: comparison with other unconjugated bile salts.

Micellization of sodium chenodeoxycholate (NaCDC) was studied for the critical micelle concentration (CMC), the micelle aggregation number, and the degree of counterion binding to micelle at 288.2, 298.2, 308.2, and 318.2 K. They were compared with those of three other unconjugated bile salts; sodium cholate (NaC), sodium deoxycholate (NaDC), and sodium ursodeoxycholate (NaUDC). The I(1)/I(3) ratio of pyrene fluorescence and the solubility dependence of solution pH were employed to determine the CMC values. As the results, a certain concentration range for the CMC and a stepwise molecular aggregation for micellization were found reasonable. Using a stepwise association model of the bile salt anions, the mean aggregation number (n) of NaCDC micelles was found to increase with the total anion concentration, while the n values decreased with increasing temperature; 9.1, 8.1, 7.4, and 6.3 at 288.2, 298.2, 308.2, and 318.2 K, respectively, at 50 mmol dm(-3). The results from four unconjugated bile salts indicate that the number, location, and orientation of hydroxyl groups in the steroid nucleus are quite important for growth of the micelles. Activity of the counterion (Na(+)) was determined by a sodium ion selective electrode in order to confirm the low counterion binding to micelles. The solubilized amount of cholesterol into the aqueous bile salt solutions increased in the order of NaUDC<NaC<NaCDC<NaDC. The first stepwise association or solubilization constants (K(1)) between a cholesterol monomer and a vacant micelle were evaluated at different bile salt concentrations. The constants were also determined for polycyclic aromatic compounds (benzene, naphthalene, anthracene, and pyrene). The corresponding DeltaG(0) value was most negative for cholesterol among the solubilizates studied, which indicated that cholesterol was thermodynamically stabilized most by solubilization into the bile salt micelles.

Bile Acids and Salts↗

PubMed2003

Temperature effect on formation of sodium cholate micelles.

The micellization of sodium cholate (NaC) at 293.2, 298.2, 303.2, 308.2, and 313.2 K by cholate anion concentration was studied over the pH range from 6.0 to 7.2. Using a stepwise association model of cholate anions without bound sodium counterions, the aggregation number (nmacr;) of the cholate micelles was evaluated and found to increase with the total concentration, indicating that the stepwise association model is applicable. The nmacr; values go up and down with increasing temperature; 17 at 298.2 and 12 at 313.2 K and at 60 mM of the sodium cholate. The fluorescence of pyrene was measured in sodium cholate solution to determine the critical micelle concentration (CMC), indicating a narrow concentration range for CMC. A sodium-ion-specific electrode was used to determine a relatively low degree of counterion binding to micelles, supporting the validity of the present association model of cholate anions. The aggregation numbers evaluated at a constant ionic strength of 0.15 and at lower but variable ionic strengths were similar except for higher cholate concentrations.

Journal Article↗

PubMed2003

Temperature effect on solubilization of n-alkylbenzenes into sodium cholate micelles.

The solubilization of n-alkylbenzenes (benzene, toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, n-pentylbenzene, n-hexylbenzene) into an aqueous micellar solution of sodium cholate was carried out. Solubilizate concentrations at equilibrium were determined spectrophotometrically at 293.2, 298.2, 303.2, 308.2, and 313.2 K. The first stepwise association constants (K(1)) between solubilizate monomers and vacant micelles were evaluated from the equilibrium concentrations and found to increase with increasing hydrophobicity of the solubilizate molecules. From the Gibbs energy change for solubilization at different micelle aggregation numbers and from the molecular structure of the solubilizates, the function of sodium cholate micelles as solubilizer was discussed. Enthalpy and entropy changes of solubilization were calculated from the temperature dependence of the K(1) values, and the solubilization was found to be enthalpy-driven for the solubilizates with shorter alkyl chains. The results obtained were also compared with those for conventional aliphatic micelles.

Journal Article↗

PubMed2002

Micelle formation of sodium deoxycholate and sodium ursodeoxycholate (part 1).

Micellization of sodium deoxycholate (NaDC) and sodium ursodeoxycholate (NaUDC) was studied for the critical micelle concentration (CMC), the micelle aggregation number, and the degree of counterion binding to micelle, where sodium cholate (NaC) was used as a reference. The fluorescence probe technique of pyrene was employed to determine accurately the CMC values for the bile salts, which indicated that a certain concentration range of CMC and a stepwise aggregation for micellization were reasonable. The temperature dependences of micellization for NaDC and NaUDC were studied at 288.2, 298.2, 308.2, and 318.2 K by aqueous solubility change with solution pH. Aggregations of the bile salt anions were analyzed using the stepwise association model and found to grow in size with increasing concentration, which confirmed that the mass action model worked quite well. The average aggregation number was found to be 2.5 (NaUDC) and 10.5 (NaDC) at the concentration of 20 mM and at 308.2 K. The aggregation number determined by static light scattering also agreed well with those by the solubility method in the order of size: NaUDC<NaC<NaDC at 308.2 K. The results indicated that the location of the OH group at C-7 and its orientation were the most important factors from the viewpoint of chemical structure for the growth of micelles. The activity measurement for sodium ions was made by a sodium ion selective electrode in order to confirm the low counterion binding to micelles and the validity of the present association model of bile salts, but the model did not hold good for NaDC at higher concentrations.

Deoxycholic Acid↗

PubMed2002

Solubilization of cholesterol and polycyclic aromatic compounds into sodium bile salt micelles (part 2).

The aqueous solubility of cholesterol was determined over the temperature range from 288.2 to 318.2 K with intervals of 5 K by the enzymatic method. The solubility was (3.7+/-0.3)x10(-8) mol dm(-3) (average +/- S.D.) at 308.2 K. The maximum additive concentrations of cholesterol into the aqueous micellar solutions of sodium deoxycholate (NaDC), sodium ursodeoxycholate (NaUDC), and sodium cholate (NaC) were spectrophotometrically determined at different temperatures. The cholesterol solubility increased in the order of NaUDC<NaC<NaDC; for example, 0.10 for NaUDC, 0.61 for NaC, and 2.99 mmol dm(-3) for NaDC at the concentration of 60 mmol dm(-3) and at 308.2 K. The same solubilization experiments were made at 308.2 K using polycyclic aromatic compounds (benzene, naphthalene, anthracene, pyrene) as a reference. Their solubility increase for the bile salts was in the same order as above. Thermodynamic analysis was made for the solubilization, where a micelle was regarded as a chemical species. The average number of solubilizate per micelle was less than unity throughout the experiments. From the Gibbs energy change for solubilization at the different mean aggregation numbers, the function of bile salt micelles was discussed from the viewpoint of molecular structure of solubilizates. The DeltaG(0) value for cholesterol was most negative among the solubilizates studied, which reflected that solubilization of cholesterol into bile salt micelles brought about largest thermodynamic stabilization.

Anthracenes↗