Weijie Yang

Antibacterial Activities of Flavonoids: Structure-Activity Relationship and Mechanism

Flavonoids are well known as antibacterial agents against a wide range of pathogenic microorganism. With increasing prevalence of untreatable infections induced by antibiotic resistance bacteria, flavonoids have attracted much interest because of the potential to be substitutes for antibiotics. In this review, the structure-relationship of flavonoids as antibacterial agents is summarized, and the recent advancements on the antibacterial mechanisms of flavonoids are also discussed. It is concluded that hydroxyls at special sites on the aromatic rings of flavonoids improve the activity. However, the methylation of the active hydroxyl groups generally decreases the activity. Besides, the lipopholicity of the ring A is vital for the activity of chalcones. The hydrophobic substituents such as prenyl groups, alkylamino chains, alkyl chains, and nitrogen or oxygen containing heterocyclic moieties usually enhance the activity for all the flavonoids. The proposed antibacterial mechanisms of flavonoids are as follows: inhibition of nucleic acid synthesis, inhibition of cytoplasmic membrane function, inhibition of energy metabolism, inhibition of the attachment and biofilm formation, inhibition of the porin on the cell membrane, alteration of the membrane permeability, and attenuation of the pathogenicity.

Enantioseparation of Racemic Mixtures Based on Solvent Sublation

A method of solvent sublation was developed for the enantioseparation of racemic ofloxacin (rac Oflx) and racemic tryptophan (rac Trp). In this method, dibenzoyl-L-tartaric acid (L-DBTA) and di-(2-ethylhexyl) phosphoric acid (D2EHPA) and sodium lauryl sulfate (SDS) were used as chiral coextractants and foamer, respectively. Several important parameters influencing the separation performances, such as pH in aqueous phase, concentrations of rac mixtures, L-DBTA, D2EHPA, and SDS, were investigated. Under the optimal operation conditions, the enantiomeric excess and enantioselectivity were 60.08% and 5.58 for Oflx and 65.09% and 6.31 for Trp, respectively. The yields of D-enantiomer and L-enantiomer were 34.23% and 8.54% for Oflx and 18.59% and 3.93% for Trp, respectively. The results suggest that the enantioselectivities have been enhanced compared with the traditional chiral extraction. This technique is an efficient chiral separation method, with many advantages such as low expenditures of organic solvent, low consumption of chiral extractant, and easy realization of multistage operation.

Adsorption and Removal of Sudan I, II from Organic Solutions by Oxidized Multiwalled Carbon Nanotubes

Sudan dyes are toxic or carcinogenic even at low concentrations, which are illegally used as additives in food products to maintain their red color and thus stimulate sales of these products in the market recently. A facile adsorption procedure for the removal of Sudan I and II in n-hexane using oxidized multi-walled carbon nanotubes (O-MWCNTs) is presented in this paper. The effect of absorp- tion conditions including absorption time, amount of adsorbent, initial concentration of Sudan I and II was examined. Two isotherm models were used to describe the adsorption equilibrium, while three kinetic models were applied to evaluate the adsorption process. The adsorption process and equilibrium for Sudan I and II were all proved to be fitted by the Langmuir model and second-order kinetic model. The O-MWCNTs possessed fast kinetics for Sudan I and II from n-hexane solvent with each saturation time of <30 min, and cor- respondingly the maximum adsorption capacities for Sudan I and II were 41.408 mg/g and 47.037 mg/g, respectively.

ENANTIOSELECTIVE EXTRACTION OF RACEMIC OFLOXACIN BY DI(2-ETHYLHEXYL)PHOSPHORIC ACID AND TARTARIC ACID DERIVATIVES AS MIXED COMPLEX CHIRAL SELECTORS

The distribution behavior of ofloaxcin (OFLX) enantiomers in a two-phase system was examined using a new mixed complex chiral selector consisting of di(2-ethylhexyl) phosphoric acid (D2EHPA) and two tartaric acid derivatives with n-octanol as diluents. The influence of composition of mixed complex chiral selector, initial concentration of OFLX, pH of aqueous phase and temperature was investigated. A maximum enantioselectivity of 2.43 was obtained when the molar concentration ratio of L-(-)-DBTA to L-(-)-DTTA is 2:3 L-(-)-DTTA concentration 0.18 mol/L, L-(-)-DBTA concentration 0.12mol/L) and the pH of aqueous phase is 6.86 at 25°C, with Dd and Dl up to a relative high value of 10.2 and 4.20, respectively. The results indicated a useful way of searching new efficient chiral selectors and it was proved also helpful to optimize the extraction systems and realize the large-scale production of the pure isomer of racemic mixtures with extraction methods.