| Magnetic resonance imaging (MRI) is one of the most important medical diagnostic techniques in clinical. Therefore MRI plays an important role in diagnosis and localization of tumor. However, the sensitivity of MRI is low so Contrast agent (CA) is necessary to be used to improve contrast by changing the relaxation time of proton. The clinical used MRI contrast agents are of high osmotic pressure, low imaging efficiency and poor selectivity. Therefore, in order to obtain high relaxation, low toxicity with tissue selective MRI contrast agents, researchers have prepared a lot of DTPA derivatives by introducing special funtional group, which becomes the mainstream in the field of micromolecule paramagnetic MRI contrast agents.In this thesis, we evaluated the stability by fluorescence spctra and aimed to investigate the properties, such as toxicity, relaxation and antibacterial activity, of ethylenediamine-N,N-di (4-amino salicylic acid)-diacetic acid(L1) and diethylenetriamine-N,N-di(4-amino salicylic acid)-triacetic acid(L2) with their corresponding gadolinium chelates through tests. Based on the performance evaluation of ligands and chelates, we discussed the relationship between structures and properties as follow:(1) We tested the fluorescence properties of ligands(4-ASA, EDTA, DTPA, L1, L2) and interactions between ligands(L1, L2) and metal ions by fluorescence spectra. The results showed that the fluorescence emission intensity of ligands(L1, L2) were from4-ASA and higher than4-ASA. Interaction between L1, L2and metal ions was investigated by fluorescence titration. According to the Benesi-Hildebrand and Job’s plot, we could confirm that L1and L2chelated with Gd3+, Cu2+and Ca2+in1:1molar ratio. The relative order of the chelating ability for GdⅢ, CuⅡ and CaⅡ at pH7.4of L1and L2was as follows:KL-CuⅡ(KL1-CuⅡ=1.267×105,KL2-CuⅡ=4.484×104)>K L-GdⅢ(KL1-GdⅢ=4.339x104, KL2-GdⅢ=2.819x104)>KL-CaⅡ (KL1-Ca1=7.219x103KL2-CaⅡ=7.619×103). What’s more, endogenous ions had barely effect on the stability of Li-Gd and L2-Gd. Finally it is reasonable to select pH7.4as the optimal pH in fluorescence spectra study.(2) We evaluated the cytotoxicity of chelates on Hela and MG-63cell lines by MTT test initially. Compared with DTPA-Gd and free gadolinium, the cytotoxicity for ligands and chelates were ranked as follows:IC50(mmol-L-1) for Hela cell lines,/C50(DTPA-Gd)=0.4665<IC5o(L2-Gd)=0.5856</C50(L1-Gd)-0.7900and for MG-63cell lines,/C50(DTPA-Gd)=0.3532</C50(L2-Gd)=0.4147</C50(L1-Gd)=0.4790. The results indicated that the cytotoxicity of L1-Gd and L2-Gd were lower than DTPA-Gd and L2-Gd exhibited higer toxic than L1-Gd. According to the stability in second part(KL1-GdⅢ==4.339x104> KL2-GdⅢ=2.819x104), we found that the cytotoxicity of L1-Gd and L2-Gd may be related to their stability.(3) The longitudinal relaxation times T1of five different concentrations of L2-Gd and DTPA-Gd was confirmed by inversion recovery. From the fitted equation in plot of1/T1against concentration, the relaxivity R1of L2-Gd was7.139mmol-1·L·S-1, which was more greater than the small molecular weight DTPA-Gd(4.371mmol-1·L·S-1). In vivo relaxation imaging of L2-Gd was tested by weighted spin echo imaging. Resulted showed that the imaging of mice was clear but without tissue selective.(4) The vitro antibacterial activities of L1, L2, L1-Gd, L2-Gd on Salmonella, E.Coli, S.Aureus and L.Monocytogenes were tested by filter paper method and broth microdilution method. The experiment results demonstrated that both ligands(L1, L2) and chelates(L1-Gd, L2-Gd) showed definite antibacterial activity. In additon, chelates exhibited either comparable or increased antimicrobial effect than ligands. Last but not the least, ligands and chelates proved to be more active against Gram-negative bacterial than Gram-positive bacterial. |
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