3:00 PM - 3:15 PM
[AAS11-23] Inherent ultraviolet absorption of unsaturated fatty acid: oleic acid as a case study
Keywords:photochemistry, ultraviolet absorption
Fatty acids are common chemical compounds found in the lipids of animals and plants. Especially, oleic acid [CH3(CH2)7CH=CH(CH2)7C(O)OH] is a representative unsaturated fatty acid and thus one of the essential chemical substances for life. Sampling observation studies show that oleic acid is also present in the sea surface micro layer [1]. Considering its hydrophobic nature, oleic acid should preferentially be located at the air-water interface. For example, Kawamura and Gagosian reported the predominant presence of the C9 carboxylic acid (i.e., nonanoic acid) in marine aerosols, and proposed that the photo-oxidative production of unsaturated fatty acids, such as oleic acid [2]. Studying photochemical reactions of oleic acid is thus important to understand the chemical composition of the atmosphere. However, our understanding of photochemistry of unsaturated fatty acid is still at an early stage [3]. In 2023, our group revealed that impurities intrinsically in nonanoic acid reagents significantly contribute to their ultraviolet (UV) absorption of wavelength >250 nm [4]. This study suggests that the contribution of impurities to the UV absorption of unsaturated fatty acids, containing oleic acid, should be reevaluated with care [5].
This study experimentally demonstrates that the UV absorption ranging from 210 nm to 380 nm of oleic acid reagents are severely affected by races of impurities in the reagents. In this study, oleic acid reagent (99.7%: BLDpharm) was purified by recrystallization at -27℃ under anaerobic atmosphere [4], and the UV spectrum is compared with those of acetic acid and nonanoic acid for a quantitative evaluation of the impurity contribution. The present results strongly suggest that there is no universal purification method for fatty acids and thus the development of a specific purification method is required. In addition, theoretical approach is also desirable for understanding the physical origin of the UV absorption of unsaturated fatty acids. In the presentation, qualitative results of quantum chemical calculations will be presented to understand the essential role of carboxylic group in UV absorption.
[1] G. G. Kattner et al., Marine Chemistry., 6, 233 (1978)
[2] K. Kawamura et al., Nature., 325, 330 (1987)
[3] S. Enami et al., J. Phys. Chem. A., 128, 5419 (2024)
[4] Saito et al., Sci. Adv., 9, 38, eadj6438 (2023).
[5] R. L. Arudi et al., J. Lipid Res., 24, 485 (1983)
This study experimentally demonstrates that the UV absorption ranging from 210 nm to 380 nm of oleic acid reagents are severely affected by races of impurities in the reagents. In this study, oleic acid reagent (99.7%: BLDpharm) was purified by recrystallization at -27℃ under anaerobic atmosphere [4], and the UV spectrum is compared with those of acetic acid and nonanoic acid for a quantitative evaluation of the impurity contribution. The present results strongly suggest that there is no universal purification method for fatty acids and thus the development of a specific purification method is required. In addition, theoretical approach is also desirable for understanding the physical origin of the UV absorption of unsaturated fatty acids. In the presentation, qualitative results of quantum chemical calculations will be presented to understand the essential role of carboxylic group in UV absorption.
[1] G. G. Kattner et al., Marine Chemistry., 6, 233 (1978)
[2] K. Kawamura et al., Nature., 325, 330 (1987)
[3] S. Enami et al., J. Phys. Chem. A., 128, 5419 (2024)
[4] Saito et al., Sci. Adv., 9, 38, eadj6438 (2023).
[5] R. L. Arudi et al., J. Lipid Res., 24, 485 (1983)