title: Understanding the properties of the coagel and gel phases: a 2H and 13C NMR study of amphiphilic ascorbic acid derivatives.
abstract: The coagel and gel phases formed by the d and l diastereoisomers of ascorbyl-dodecanoate (ASC12) in deuterated water were studied through solid-state NMR techniques. In particular, the dynamic properties of water and surfactant chains were investigated by (2)H and (13)C NMR static spectra, respectively. Two fractions of water with very different dynamics were found in the coagel phases, one solidlike and one liquidlike, assigned to water strongly bound to the surfactant polar heads and bulk water, respectively. Only one kind of "intermediate" water was instead detected in the gel phase suggesting that the merging of the two types of water in the interlayers between the surfactant lamellae occurs at the coagel-to-gel transition. Moreover, the surfactant chains, very rigid in the coagel phase, give rise to fast trans-gauche interconformational jumps in the gel phase, where almost isotropic reorientations of the whole aggregates also occur. A different dynamic behavior was found for the two diastereoisomers in particular for what concerns the surfactant molecules in the gel phase and the water molecules in the coagel presumably ascribable to different inter- and intramolecular interactions that involve the polar heads.
authors.affiliation: Department of Chemistry and Industrial Chemistry, University of Pisa, via Risorgimento 35, 56126 Pisa, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Borsacchi
authors.forename: Moira
authors.initials: M
authors.lastname: Ambrosi
authors.forename: Pierandrea
authors.initials: P
authors.lastname: Lo Nostro
authors.forename: Marco
authors.initials: M
authors.lastname: Geppi
mesh_terms: D001205:Ascorbic Acid / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D002247:Carbon Isotopes; D003903:Deuterium / Q000737:chemistry*; D005782:Gels / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000592:standards; D008823:Micelles; D008968:Molecular Conformation; D012015:Reference Standards; D013237:Stereoisomerism
chemical_list: D002247:Carbon Isotopes; D005782:Gels; D008823:Micelles; D003903:Deuterium; D001205:Ascorbic Acid