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The complexation equilibria of L-norvaline (Nva) and ferulic acid (FA) were studied in aqueous solutions at room temperature (298 K) and in fixed ionic strength (0.15 mol 3 dm -3 NaNO 3 ) by means of potentiometry and spectrophotometry techniques. The ferric (Fe 3þ ), chromium (Cr 3þ ), and cupric (Cu 2þ ) complexing capacities of Nva and FA and their overall stability constants in aqueous solutions were obtained by the HYPERQUAD 2008 program from the potentiometric data. The concentration distributions of the various complex specia in solution were evaluated and discussed. The spectroscopic UV-visible measurements are carried out to give qualitative information about the confirmation of the complexes formed in these solutions. ' INTRODUCTIONIt is known that nonprotein amino acids, which are common in fodder plants, consumed animal feeds, and human foods, are a threat to human and animal health. 1 They possess a wide array of chemical structures and often contain functional groups not commonly present in natural products. 1,2 Some act as agonists or antagonists in the neurotransmission of higher animals. 1,2 Others influence the growth of fungi and bacteria. 1,2 Norvaline (C 5 H 11 NO 2 ) is an unusual nonproteinogenic branched-chain amino acid which has been of interest particularly in early enzymological research work. 3 Recently, it has been proved that L-norvaline (Nva) has antifungal activity as it inhibits arginase thus increasing arginine concentrations. 4 More specifically, Nva has been shown to inhibit homoserine dehydrogenase. 5 Moreover, some biological studies have indicated that Nva has antitubercular and antifungal actitvities. 6,7 Also, a lot of research has been focused on the role of antioxidant ferulic acid (FA) in several biological processes. 8 Taking into account the natural occurrence, biosynthesis, metabolism, and functions of nonprotein amino acids and phenolic acids, the study of their metal complexes gains much attention and is attracting more attention in equilibrium and biological chemistry. Hence, a study of metal-Nva-FA complexes may lead to better elucidation of the behavior of such compounds in biological systems and metal-Nva-FA interactions might be of therapeutic interest. A search in the literature shows that there has been quite a number of studies reported on the interaction between metal ions and Nva. 9-27 Most of these research works investigated the complexation equilibria of the copper(II), nickel(II), cobalt(II), manganese(II), uranyl(II), terbium(III), lanthanum(III), praseodymium(III), neodymium-(III), and trimethyltin(IV) metal ions with Nva using different electroanalytical techniques. However, there is no study conducted on the iron(III) or chromium(III) metal ion binary complexes of Nva, and any metal ion-norvaline mixed ligand complexes.Our recent publications describe the protonation equilibrium phenomena of essential amino acids, 28 hydroxamic acids, 29 phenolic compounds, 30 and nonprotein Nva, 31 L-canavanine 32 amino acids in aqueous and in aqueous-organic so...

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A novel cross-flow technique for membrane filtration of bacterial cell suspensions was established. This is an air slugs entrapped cross-flow method in which air slugs were generated by introducing air into the cross-flow stream. As air slugs moved along with cross-flow, the disturbance of cell sublayer formation on membrane surface was enhanced. As a consequence, filtration flux was improved and stabilized. The effect of air slugs on improving filtration flux was more pronounced in filtering gram-negative Escherichia coli cell than gram-positive Brevibacterium flavum cell. Moreover, air slug was about 50% more effective on reducing filtration resistance using ultrafiltration (UF) membrane of 300,000 molecular weight cutoff (MWCO) than microfiltration (MF) membrane of 0.2 microm.

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