Enzymatic Synthesis Of Cephalexin-coupling With Membrane Extraction Process

Cephalexin is one of the most widely used cephalosporin antibiotics because ofits broad spectrum antimicrobial、high bioavailability and tolerance. Traditionallycephalexin is produced by chemical synthesis, causing serious pollution to theenvironment. However, enzymatic synthesis of cephalexin has the advantages ofsimple process and operation, mild reaction conditions, short cycle, no groups toprotect, clean and safe. In this paper, hollow fiber supported liquid membrane withstripping dispersion was introduced to combine the enzymatic synthesis of cephalexinwith separation process, which improves the substrate utilization and product yield.Firstly, the mechanism of HFSLM-SD extraction of cephalexin process wasintroduced, and established the overall mass transfer coefficient model of HFSLM-SDextraction of cephalexin process and got following results: under steady state, theindividual mass transfer coefficient of the feed solution(ka), membrane(km) and thestripping solution(ks) were respectively6.99×10-6m/s,1.5×10-6m/s,6.681×10-5m/s,and the total mass transfer coefficient K was3.891×10-6m/s.Secondly, the HFSLM-SD extraction experiments of cephalexin process wereconducted. Many factors investigated in detail, including the characteristics of feedand the selection of buffer solution, selection of the stripping solution, thecomposition of the organic membrane phase, and the feed concentration, volume ratio,mixing rate, stipping transmembrane pressure influence on the extraction efficiency.The optimum operating conditions obtained:0.05M carbonate buffer containing20mM cephalexin in feed phase, pH=8.0～9.0; Isopar L as organic solvent, and thevolume ratio of feed/organic=1:1; the carrier Aliquat336concentration of5wt%;stripping solution of pH=9.030mM PGME aqueous; stirring rate of400rpm;transmembrane pressure of4psi. The kinetics study of HFSLM-SD extraction ofcephalexin process was carried out.Finally, kinetic modle of enzymatic synthesis reactions of cephalexin isestablished. Calculated on the basis of experiments, the rate constant for each reactionwas as follows, k1=17.3(mM�'min)-1,2=740(min)-1, k3=174(mM�'min)-1,k-3=113(mM�'min)-1. Besides, the activity of Penicillin G acylase were investigated,discussed the choice of complexing agent, and finally enzymatic synthesis of cephalexin-coupling with membrane extraction process experiments were done toachieve a simultaneous of synthesis and separation of cephalexin. The formation ofcephalexin achieved by enzymatic synthesis reactions were determined by Fourier-Transform Infrared Spectrometer (FT-IR). The maximum yield of Cephalexin was39.7%.Enzymatic synthesis of cephalexin-coupling with membrane extraction processcan efficiently improve the yield of cephalexin and recover cephalexin from thereaction system. The method of HFSLM-SD not only simplifies operation procedures,but also improves the utilization of substrate and product yield.