Abstract: SOLUTION CHEMISTRY FOR MODELS OF ENTEROBACTIN AND TANNIN WITH URANYL IONSHENLANGTAO；LIYUN（Chian Institute of Atomic Energy,P.O.Box 275（88）,Beijing 102413）ABSTRACT The peculiar phenomenon，in which the stability constant of Fe（Ⅲ）with enterobactin se-creted by microorganisms is as high as 10~(52)，has prompted chemists to desing and synthesize thespecific sequestering agents for ferric ion and actinide ions using biomimetic approach．These spe-cific sequestering agents play important roles in the therapy of β-thalassemia，the excretion of ac-tinide elements from animal bodies，nuclear fuel reprocessing and nuclear medicine. In order to de-velop optimum design of these chelating agents the solution chemistry for models of enterobactinsuch as Tiron4，5-dihydroxy-5-benzendisulfonate， nCat4-nitrocatechol，3，4，3-LICAMSN~1,N~5,N~(10),N~(14)-tetra（2，3-dihydroxy-5-sulfobenzoyl）-tetraazatetradecane with has beeninvestigated．Tannin，which is a polyphenol and inexpensive substance，may probably be used inseparation science of nuclear industry. Therefore，the solution chemistry of Tannin with uranylion has also been studied.In this work，the behaviour of solution chemistry ，including eight systems──Tiron andTifon-U（Ⅵ）nCat and nCat－U（Ⅵ），3，4，3-LICAMsand3，4，3－LICAMS-U（Ⅵ）as well asTannin and Tannin-U（Ⅵ），has been examined by pH-spectrophotometrc titratiOn method，Therelationships between the dissociation processes of ligands，the forming processes of complexes andelectronic spectra have been discussed．The donor sites and forming conditions of complexes aredetermined．In Tiron system，phenolic group begins to dissociate at pH＞5．82，then spectrumcurves overlap at pH＞9．90；In Tiron-U（Ⅵ）system，complexes are formed within the range ofpH＝4．31-7．36，absorbances increase markedly in the band of long wave length，the shape ofits spectrum curves is different clearly from that of Tiron system，In nCat systern，phenolic proupbegins to dissociate at pH＞4．40．There is an isoabsorptive point at λ＝280nm in the range of pH＝4．40-8．50 because of dissociation equilibrium of the ligand．It is interesting that absorbancesdecrease with increasing pH within the ragen of λ＝280-350nm. At pH＝4．18-6．60，U（Ⅵ）complexes with nCat and the absorption peak（λ＝267．0nm） intensifies obviously as complexsare formed．3，4，3-LICAMS chelate U（Ⅵ）at pH＝4．25-6．25． In Tannin systeln， phenolicgroups begin to dissociate at pH＞4．95．The ccordination reactions of U（Ⅵ）and Tannin takeplace a pH＝4．47-9．03．These experiments have established that U（Ⅵ）complexes with theseligarids via phenolic groups.This work has offered important data for the design of actinide-specific sequestering agents.Key words Sequestering agent Electronic spectrum Solution chemistry