This study investigated polysiloxane hybrid sol-gel coatings synthesized from tetraethyl orthosilicate (TEOS), 3-(trimethoxysilyl)propyl methacrylate (MAPTMS) and two different precursors, i.e., methyl- or ethyl- methacrylate (MMA or EMA), as corrosion protection of aluminium alloy 7075-T6. The hypothesis was that the additional alkyl group might affect the chemical properties and, consequently, the corrosion properties. Synthesis of the sols proceeded in two steps, each involving either MMA or EMA in the same molar ratio. The resulting sols, siloxane-(poly(methyl methacrylate-co-MAPTMS)) or siloxane-(poly(ethyl methacrylate-co-MAPTMS)), were applied on aluminium alloy followed by characterization in terms of chemical structure and composition, topography, wettability, adhesion and corrosion resistance in 0.1 M sodium chloride solution. The chemical properties of sols, monoliths and coatings were investigated using Fourier transform infrared spectrometry, solid state nuclear magnetic resonance spectrometry, X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. Coatings were similar in terms of surface topography, while the wettability of the coating with EMA showed 6° greater water contact angle compared to the coating with MMA. Both coatings were shown, by electrochemical impedance spectroscopy in 0.1 M NaCl solution, to act as barriers to protect the underlying substrate in which coating with EMA exhibits better protection properties after 2 months of immersion. Adhesion tests confirmed the highest grade of adhesion to the substrate for both coatings. Testing in a salt-spray chamber demonstrated excellent corrosion protection, where coatings remaining intact after more than 600 h of exposure.

Liquidambar formosana (also known as maple) is a tall deciduous tree widely distributed in various regions of the South of the Qinling Mountains and Huaihe River in China, and also found in Northern Vietnam, Laos and South Korea. L. formosana is a famous ornamental plant for leaves are green in spring and summer, and red in autumn. Different plant parts of L. formosana, such as leaf, fruit, bark, and resin, are proved to be treasures as natural medicinal plant resources [1]. Among the bioactive constituents, several diterpenoid acids of the abietane family have been identified. Abietic acid (1) occurs in plants of the genus Abies and is the first member of a class of plant metabolites, the abietane-type diterpenoids. They are characterized by a tricyclic ring system and have shown a wide range of chemical diversity and biological activity.[2,3] Medicinal chemists have studied derivatives of two readily available materials such as dehydroabietic acid (2) and dehydroabietylamine (3, DHAA).[3] To date, there is only one commercial drug, Ecabet® [ecabet sodium (4)], based on abietanes, which is used for the treatment of reflux esophagitis and peptic ulcer disease. Ferruginol (5) exhibits anticancer effects in human ovarian cancer and inhibition of cancer cell migration. Recent studies of sugiol (6) demonstrated in vivo antitumor activity in DU145 prostate xenografts. These biological reports and the simultaneous isolation, (in 2014) by Hua and co-workers, of the new abietane liquiditerpenoic acid A (7), a sugiol analogue, from the resin of Liquidambar formosana [4] and from Pinus massoniana,[5] by Kuo and co-workers named independently as abietopinoic acid, prompted us to synthesize it and study its biological properties along with some analogues. References [1] Ouyang, X. L.; Yi, S.; Lu, H. Y.; Wu, S. M.; Zhao, H. Q. Eur. J. Med. Plants 2016, 17, 1-11. [2] For a review on this topic, see: González, M. A. Nat. Prod. Rep. 2015, 32, 684-704. [3] For a review on this topic, see: González, M. A. Eur. J. Med. Chem. 2014, 87, 834-842. [4] Shang, H.-J.; Li, D.-Y.; Wang, W.-J.; Li, Z.-L.; Hua, H.-M. Nat. Prod. Res. 2014, 28, 1-6. [5] Mohamed, H. A.; Hsieh, C.-L.; Hsu, C.; Kuo, C.-C.; Kuo, Y.-H. Helv. Chim. Acta 2014, 97, 1146-1151.