INVESTIGADORES
PALMA Santiago Daniel
artículos
Título:
Water of Hydration in Coagels
Autor/es:
AMBROSI, M.; LO NOSTRO, PIERANDREA; LAURA FRATONI,; DEI, L.; NINHAM, B.; SANTIAGO DANIEL PALMA; ALBERTO ALLEMANDI, DANIEL; BAGLIONI, P.
Revista:
Physical Chemistry Chemical Physics
Referencias:
Año: 2004 vol. 6 p. 1401 - 1407
ISSN:
1463-9076
Resumen:
Vitamin C-based alkanoyl-6-O-ascorbic acid esters, ASCn, are a class of surfactants, interesting both on
account of their phase behaviour, and of the properties of the supramolecular assemblies they form. When
dispersed in water at room, or lower, temperatures above ca. 5% w/w concentration, they form coagels. At
higher temperatures, the microstructure changes to micellar solutions for surfactants of low hydrocarbon
chain length n. The longer chained systems form gel phases. The transition enthalpy change is dominated by
rearrangements in hydrophobic chain packing. On the other hand the Krafft point seems instead to be
dictated mainly by interactions between the polar headgroups and the solvent. The coagel phase is usually
thought of as formed of surfactant lamellae separated by thin interlayers of strongly bound, essentially
frozen, water molecules. In this work, DSC measurements were performed to explore the interactions
between water and the surfactant molecules. Two kinds of water were detected: interlayer hydration water
and bulk water. The number of hydration water molecules per polar headgroup was inferred from the
experimental results. Further insights into the coagel structure were gained from X-ray diffraction and optical
microscopy. The effects of glycerin (GLY), propylene glycol (PG), and poly(ethylene glycol) (PEG), as
co-solvents were investigated by conductivity and DSC experiments. Glycerin seems to stabilize the coagel,
probably through the formation of hydrogen bonds that compete for the polar headgroups with the strongly
bound water molecules. By contrast, PG and PEG decrease the compactness of the lamellar structure. This is
most likely because these compounds can penetrate into the lipid portion of the lamellae, and reduce the
hydrophobic interactions that hold the compact assemblies together.O-ascorbic acid esters, ASCn, are a class of surfactants, interesting both on
account of their phase behaviour, and of the properties of the supramolecular assemblies they form. When
dispersed in water at room, or lower, temperatures above ca. 5% w/w concentration, they form coagels. At
higher temperatures, the microstructure changes to micellar solutions for surfactants of low hydrocarbon
chain length n. The longer chained systems form gel phases. The transition enthalpy change is dominated by
rearrangements in hydrophobic chain packing. On the other hand the Krafft point seems instead to be
dictated mainly by interactions between the polar headgroups and the solvent. The coagel phase is usually
thought of as formed of surfactant lamellae separated by thin interlayers of strongly bound, essentially
frozen, water molecules. In this work, DSC measurements were performed to explore the interactions
between water and the surfactant molecules. Two kinds of water were detected: interlayer hydration water
and bulk water. The number of hydration water molecules per polar headgroup was inferred from the
experimental results. Further insights into the coagel structure were gained from X-ray diffraction and optical
microscopy. The effects of glycerin (GLY), propylene glycol (PG), and poly(ethylene glycol) (PEG), as
co-solvents were investigated by conductivity and DSC experiments. Glycerin seems to stabilize the coagel,
probably through the formation of hydrogen bonds that compete for the polar headgroups with the strongly
bound water molecules. By contrast, PG and PEG decrease the compactness of the lamellar structure. This is
most likely because these compounds can penetrate into the lipid portion of the lamellae, and reduce the
hydrophobic interactions that hold the compact assemblies together.ca. 5% w/w concentration, they form coagels. At
higher temperatures, the microstructure changes to micellar solutions for surfactants of low hydrocarbon
chain length n. The longer chained systems form gel phases. The transition enthalpy change is dominated by
rearrangements in hydrophobic chain packing. On the other hand the Krafft point seems instead to be
dictated mainly by interactions between the polar headgroups and the solvent. The coagel phase is usually
thought of as formed of surfactant lamellae separated by thin interlayers of strongly bound, essentially
frozen, water molecules. In this work, DSC measurements were performed to explore the interactions
between water and the surfactant molecules. Two kinds of water were detected: interlayer hydration water
and bulk water. The number of hydration water molecules per polar headgroup was inferred from the
experimental results. Further insights into the coagel structure were gained from X-ray diffraction and optical
microscopy. The effects of glycerin (GLY), propylene glycol (PG), and poly(ethylene glycol) (PEG), as
co-solvents were investigated by conductivity and DSC experiments. Glycerin seems to stabilize the coagel,
probably through the formation of hydrogen bonds that compete for the polar headgroups with the strongly
bound water molecules. By contrast, PG and PEG decrease the compactness of the lamellar structure. This is
most likely because these compounds can penetrate into the lipid portion of the lamellae, and reduce the
hydrophobic interactions that hold the compact assemblies together.n. The longer chained systems form gel phases. The transition enthalpy change is dominated by
rearrangements in hydrophobic chain packing. On the other hand the Krafft point seems instead to be
dictated mainly by interactions between the polar headgroups and the solvent. The coagel phase is usually
thought of as formed of surfactant lamellae separated by thin interlayers of strongly bound, essentially
frozen, water molecules. In this work, DSC measurements were performed to explore the interactions
between water and the surfactant molecules. Two kinds of water were detected: interlayer hydration water
and bulk water. The number of hydration water molecules per polar headgroup was inferred from the
experimental results. Further insights into the coagel structure were gained from X-ray diffraction and optical
microscopy. The effects of glycerin (GLY), propylene glycol (PG), and poly(ethylene glycol) (PEG), as
co-solvents were investigated by conductivity and DSC experiments. Glycerin seems to stabilize the coagel,
probably through the formation of hydrogen bonds that compete for the polar headgroups with the strongly
bound water molecules. By contrast, PG and PEG decrease the compactness of the lamellar structure. This is
most likely because these compounds can penetrate into the lipid portion of the lamellae, and reduce the
hydrophobic interactions that hold the compact assemblies together.