2 methoxycinnamaldehyde

Cinnamon phytochemicals, including cinnamic acid, cinnamyl alcohol, cinnamyl acetate, cinnamaldehyde, 2-methoxy cinnamaldehyde and α-methyl cinnamaldehyde, dimethyl sulfoxide (DMSO), phorbol 12-myristate 13-acetate (PMA), LPS (Escherichia coli O55:B5), adenosine triphosphate (ATP), 3-(4,5-dimethyldiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and trichloroacetic acid (TCA) were procured from Sigma-Aldrich (St. Louis, MO, USA). The medium and reagents for cell culture were purchased from Thermo Fisher Scientific (Grand Island, NE, USA). Chemicals of analytical grade were used.

Trans-cinnamaldehyde (99%) and 10 of its derivatives: cinnamaldehyde oxime (95%), α-methylcinnamaldehyde (95%), 2-methoxycinnamaldehyde (95%), 2-nitrocinnamaldehyde (98%), 4-bromocinnamaldehyde (95%), 4-methoxycinnamaldehyde (95%), 4-nitrocinnamaldehyde (95%), 4-dimethylaminocinnamaldehyde (98%), 4-fluorocinnamaldehyde (97%), and 4-chlorocinnamaldehyde (95%) were purchased from Sigma-Aldrich (St. Louis, MO, USA) or Combi-Blocks (San Diego, CA, USA). Their molecular weights and chemical structures are given in Table 1. Stocks of 100 mg/ml were prepared in dimethyl sulfoxide (DMSO) and kept at −20°C until required. A total of 0.1% (v/v) DMSO was used as the control for antibacterial and biofilm experiments; at this concentration DMSO did not effect on bacterial growth or biofilm formation.

Cinnamaldehyde, cinnamic acid, cinnamyl alcohol, coumarin, and 2-methoxyCinnamaldehyde were purchased from Sigma-Aldrich (purity: > 99%, St. Louis, MO). Acetonitrile, methanol, and water purcahsed from J.T. Baker (high-performance liquid chromatography (HPLC) grade, Phillipsburg, NJ). Formic acid was obtained from Merck (Darmstadt, Germany).