Association and Phase Behavior of Cholic Acid-Modified Dextran and Phosphatidylcholine Liposomes

The interaction between liposomes (1,2-dimyristoyl-<i>sn</i>-glycero-3-phosphocholine (DMPC)) and a hydrophobically modified water-soluble polymer (HMP; a bile acid-modified dextran) has been investigated by isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC), combined with turbidity measurement and cryogenic scanning electron microscopy (cryo-SEM). The thermodynamic information on the association (enthalpy of interaction, enthalpy of transition of mixed vesicles to mixed micelle-like aggregates) was obtained from ITC. Further, the phase behavior for the system could be derived from the ITC measurements, and be confirmed by turbidity and cryo-SEM. The effect of cholic acid (CA) side groups on the ordered arrangement of DMPC bilayers was studied by DSC, by following the changes they induce in the gel-to-liquid crystalline liposome phase transition. The DSC results were in excellent agreement with the interpretation proposed for the ITC results. The morphology of the aggregates, as characterized by cryo-SEM, is in line with the proposed aggregate morphologies

Conductivities of 1‑Alkyl-3-methylimidazolium Chloride Ionic Liquids in Disaccharide + Water Solutions at 298.15 K

Conductivities for ionic liquids (ILs) 1-alkyl-3-methylimidazolium chloride ([C_<i>n</i>mim]­Cl, <i>n</i> = 4, 6, 8, 10) + sucrose + water solutions and [C₄mim]­Cl + maltose + water solutions were measured at 298.15 K. Meanwhile, densities, viscosities, and relative permittivities for water + disaccharide mixtures were also measured. The Lee–Wheaton conductivity equation was used to acquire the limiting molar conductivities (Λ₀). The Walden products (Λ₀η₀) were also calculated. The interaction of ILs with disaccharide was discussed in terms of the structure of disaccharides and ILs. Furthermore, values of Λ₀ for inorganic salts (ordinary electrolyte, such as NaCl/KCl) and ILs (special electrolyte) were compared, indicating that they have approximate limiting molar conductivities, namely, they have not too much difference in electrical conductivity

Calorimetric and Theoretical Study of the Interaction between Some Saccharides and Sodium Halide in Water

Dilution enthalpies and mixing enthalpies of sodium halide and some saccharides (glucose, galactose, xylose, arabinose, fructose, and sucrose) in aqueous solution were determined by calorimetric measurements at 298.15 K. The values were used to determine enthalpic pair interaction parameters. Combined with Gibbs energy pair parameters, entropic pair interaction parameters were also obtained. Theoretical calculations at the B3LYP/6-311++G­(d,p) level were carried out to provide the information of structures and thermodynamic functions. The information reveals the thermodynamic essence of the interactions between sodium halide and saccharides in aqueous solutions. The experimental results and theoretical calculations show that the sign of enthalpic pair interaction parameter 2<i>υh</i>_ES is determined by the direct interaction between saccharides and ions, whereas the difference in value of 2<i>υh</i>_ES for different saccharides or electrolytes depends on the partial dehydration of saccharides or anions in aqueous solution. The difference in value of entropic pair interaction parameters depends partly on the different dominant interactions in the process of partial dehydration of saccharides or ions. An enthalpy–entropy compensation relationship was observed for the sodium bromide–aldopyranose–water systems. Remarkably, it can be conjectured that the hydration entropy of glucose is lower than for other monosaccharides. Perhaps it is one of the reasons why glucose plays an important role in living organisms rather than other monosaccharides

Self-Aggregation of Amphiphilic Dendrimer in Aqueous Solution: The Effect of Headgroup and Hydrocarbon Chain Length

The self-aggregation of amphiphilic dendrimers G₁QPAMC_<i>m</i> based on poly­(amidoamine) PAMAM possessing the same hydrophilic group but differing in alkyl chain length in aqueous solution was investigated. Differences in the chemical structures lead to significant specificities in the aggregate building process. A variety of physicochemical parameters presented monotonous regularity with the increase in alkyl chain length in multibranched structure, as traditional amphiphilic molecules. A significant difference, however, existed in the morphology and the microenvironment of the microdomain of the aggregates, with G₁QPAMC_<i>m</i> with an alkyl chain length of 16 intending to form vesicles. To obtain supporting information about the aggregation mechanism, the thermodynamic parameters of micellization, the free Gibbs energy Δ<i>G</i>_mic, and the entropy Δ<i>S</i>_mic were derived subsequently, of which the relationship between the hydrophobic chain length and the thermodynamic properties indicated that the self-assembly process was jointly driven by enthalpy and entropy. Other than traditional surfactants, the contribution of enthalpy has not increased identically to the increase in hydrophobic interactions, which depends on the ratio of the alkyl chain length to the radius in the headgroup. Continuous increases in the hydrophobic chain length from 12 to 16 lead to the intracohesion of the alkyl chain involved in the process of self-assembly, weakening the hydrophobic interactions, and the increase in −Δ<i>H</i>_mic, which offers an explanation of the formation of vesicular structures