Thermal Behavior of Anhydrous Ascorbic Acid 6‐Palmitate with Trace of Decomposition. Issue 32 (27th August 2020)

• Record Type: Journal Article
• Authors: Ogawa, Shigesaburo; Hirase, Ryuji; Ohishi, Tomoyuki; Hara, Setsuko; Takahashi, Isao
• Is Part Of: ChemistrySelect. Volume 5:Issue 32(2020)
• Page Start: 10022
• Page End: 10028
• Publication Date: 2020-08-27
• Subjects: Liquid crystals -- Phase transitions -- Surface analysis -- Vitamins -- X-ray diffraction; Chemistry -- Periodicals; 540.5
• DOI: 10.1002/slct.202002800
• Languages: English
• ISSNs: 2365-6549

Abstract

Abstract: Ascorbic acid 6‐palmitate (AsP) is an industrially utilized antioxidant and amphiphilic lipid, which forms a liquid crystalline (LC) phase. Herein, we describe the basic thermal behavior of AsP under anhydrous condition. Grazing‐incidence wide‐angle X‐ray‐diffraction (GI‐WAXD) measurements using a two‐dimensional detector (2D‐GI‐WAXD) and perpendicularly aligned AsP films, together with thermal analysis, showed that the AsP forms only a lamellar LC phase above its melting point ( T m ); however, when the LC phase was cooled to facilitate annealing and recrystallization, crystals (Cr) formed with a low degree of crystallinity. Furthermore, a composite system, consisting of the Cr phase and LC phase of AsP, was obtained upon reheating. These anomalous phenomena were likely caused by trace dimerization and decomposition of AsP at a temperature just above T m, although thermal decomposition accompanied by weight reduction occurred at a much higher temperature in the isotropic phase (IL). Thus, the basic thermal behavior of AsP, which is essential for its use, was unveiled. Abstract : Grazing‐incidence wide‐angle X‐ray diffraction using a two‐dimensional detector (2D‐GI‐WAXD) and aligning films unveiled the basic but strange thermal behavior of the representative antioxidant, ascorbic acid 6‐palmitate (AsP), which was non‐reversible. A crystal (Cr) with a low degree of crystallinity and a composite system, consisting of the Cr phase and liquid crystal phase, were obtained owing to trace dimerization and decomposition. This behavior can greatly affect the usability of AsP as the self‐assembling motif in the cosmetics and pharmaceutical industries.