To study oxazine ring formation in benzoxazine synthesis from phenol, primary amine and formaldehyde, reactions between 2-phenylaminomethylphenol (Mannich base) and formaldehyde in homogeneous dioxane/water solution are researched. Reaction orders, rate constants at different temperatures, and activation energy are calculated, the process of reaction is proposed, and the influence of acid and base is discussed. The reaction can occur at low temperature and generate the product 3,4-dihydro-2H-3-phenyl-1,3-benzoxazine. No intermediate 2-(N-hydroxymethyl-N-phenylamino)methylphenols are observed. The concentration of a Mannich base has little effect on the reaction rate, while the reaction is first-order to formaldehyde. Based on chemical properties of formaldehyde in aqueous solution, the reaction process includes the following three steps: degradation of poly(oxymethylene) glycols to methylene glycol, dehydration of methylene glycol to formaldehyde molecule, and the reaction between a Mannich base and formaldehyde molecule to benzoxazine. Dehydration of methylene glycols to formaldehyde molecules is the rate-controlling step.
Mono-(2-ethylhexyl) phthalate (MEHP), the active metabolite of di-(2-ethylhexyl) phthalate (DEHP), is a widespread environmental contaminant and has been proved to have potential adverse effects on the reproductive system, carcinogenicity, liver, kidney and developmental toxicities. However, the effect of MEHP on vascular system remains unclear. The main purpose of this study was to evaluate the cytotoxic effects of MEHP on human umbilical endothelial cells (HUVEC) and its possible molecular mechanism. HUVEC cells were treated with MEHP (0, 6.25, 12.5, 25,50 and 100 µM), and the cellular apoptosis and mitochondrial membrane potential as well as intracellular reactive oxygen species were determined. In present study, MEHP induced a dose-dependent cell injury in HUVEC cell via an apoptosis pathway as characterized by increased percentage of sub-G1, activation of caspase-3, -8and -9, and increased ratio of Bax/bcl-2 mRNA and protein expression as well as cytochrome C releasing. In addition, there was obvious oxidative stress, represented by decreased glutathione level, increased malondialdehyde level and superoxide dismutase activity. N-Acetylcysteine, as an antioxidant that is a direct reactive oxygen species scavenger, could effectively block MEHP-induced reactive oxygen species generation, mitochondrial membrane potential loss and cell apoptosis. These data indicated that MEHP induced apoptosis in HUVEC cells through a reactive oxygen species-mediated mitochondria-dependent pathway.
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