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Antibacterial activity of indigenous Dayak onion (Eleutherine palmifolia (L.) Merr) was investigated. The Dayak onion was solvent extracted with n-hexane, ethyl acetate, and ethanol 96% consecutively. Each extract was tested its antibacterial activity towards methicillin-resistant Staphylococcus aureus (MRSA), Bacillus cereus, Shigella sp., and Pseudomonas aeruginosa using disc diffusion method. The test results showed that the n-hexane, ethyl acetate, and ethanol 96% extracts positively inhibited the growth of MRSA, B. cereus, Shigella sp., and P. aeruginosa. The highest inhibition activity of each extract was obtained with 10 mg/mL of extract concentration; whereas the minimum inhibitory concentration (MIC) of each extract was 2 mg/mL. Extract with the highest inhibition activity was ethyl acetate extract against B. cereus (139.58%). TLC evaluation of ethyl acetate extract showed four spots and bioautography indicated that ethyl acetate extract contained four types of compounds with inhibition activity against B. cereus, in which two compounds have higher antibacterial activity than the other two.

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We provide evidence for CH-based nonconventional hydrogen bonds (H-bonds) for 10 Lewis antigens and two of their rhamnose analogues. We also characterize the thermodynamics and kinetics of the H-bonds in these molecules and present a plausible explanation for the presence of nonconventional H-bonds in Lewis antigens. Using an alternative method to simultaneously fit a series of temperaturedependent fast exchange nuclear magnetic resonance (NMR) spectra, we determined that the H-bonded conformation is favored by ∼1 kcal/mol over the non-H-bonded conformation. Additionally, a comparison of temperature-dependent 13 C linewidths in various Lewis antigens and the two rhamnose analogues reveals H-bonds between the carbonyl oxygen of the N-acetyl group of N-acetylglucosamine and the OH2 group of galactose/fucose. The data presented herein provide insight into the contribution of nonconventional H-bonding to molecular structure and could therefore be used for the rational design of therapeutics.

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