Synthesis And Gelation Properties Of Tyrosine Derivatives

Low-molecular-mass organic gels (LMOG) have numerous potential practicalapplications in preparation of nano materials, environmental management, drug delivery, etc,which is due to their completely thermal reversibility, special self-assembly,stimuli-responsible and other properties. It is an important research direction in this field howto design and synthesize simple gelator molecules, easy to synthesize and available in largequantities from cheap starting materials, and study the relation between their structure and gelperformance.In this thesis, new tyrosine-based gelators were designed and synthesized. The relationbetween gelation properties and the structure of these tyrosine-based molecules, as well as themorphology and molecular packing fashion of LMOG were studied. On this basis, the BDThydrogel have been investigated in the feld of drug delivery.(1) The results from TLC,1H-NMR and FTIR analysis confirmed that new Tyrosinederivatives, namly, Boc-O-docyl-L-tyrosine (BDT), didodecyl-L-tyrosine methylester-1,6-adipamide (TEDHB), didodecyl L-tyrosine-1,6-adip-amide (TDHB),Boc-O-docyl-L-tyrosine methyl ester (BDTE) and docyl-L-tyrosine methyl ester (DTE) hadbeen synthesized from cheap and renewable Boc-L-tyrosine methyl ester at room temperature.(2) The gelation behavior of five Tyrosine derivatives, namly, BDT, TEDHB, TDHB,BDTE and DTE was systematically studied in eighteen different common solvents. Theresults showed that TEDHB could gel alkane solvents, DMSO and vegetable oil; TDHB couldgel benzene, and could gel trichloromethane under ultrasound assistance; TDHB and BDTcould form pH-sensitivity hydrogel. Though these tyrosine derivatives had a little differencein structure, their gelling behavior was significant different.(3) The minimal gelation concentration (MGC) of TEDHB in four different alkanesolvents, namely, normal hexane, cyclohexane, n-heptane, n-octane were observed and theinfluence of TEDHB concentrations on gel-solution transition temperature (TGS) were studied. The results showed that the MGC decreased with increase the number of carbon atoms inalkane solvents, and TGSof TEDHB-octane gel increased with increase TEDHBconcentration.(4) SEM observation found different morphology such as fibrous network structures,layered structures and3D helical network structures from different gel systems. Themorphology was various deponding on different geltors, solvents and concentration of geltor.FTIR analysis showed that the hydrogen bonding interaction played important role in theprocess of organogel formation. The hydrogen bonding interaction was weaker in the gel statethan that in solid state for TDHB and BDT; the ratio of different hydrogen bonding waschanged in the process of TDHB-chloroform gel formation. With combining the results fromUV and XRD analysis we proposed possible stacking mechanism of the molecules in gels.(5) The influence of CPFX on TGSand viscoelasticity of BDT hydrogel were studied.The results showed that the incorporation of CPFX had similar affect on TGSandviscoelasticity of BDT hydrogel; At low CPFX concentration, the TGSand viscoelasticity ofBDT gel steadily increased with increase of CPFX, achieved maximum at CPFX/BDT=0.3,but interestingly the TGSdecreased with increase of CPFX further. Base on the SEM analysisand the structure characteristics of CPFX and BDT, it was hypothesized that there are threedifferent existing ways in the hydrogel.(6) Release behavior of CPFX from BDT hydrogel was invested under static diffusion.The results showed that The CPFX release amount increased with increase of CPFX in BDTgel when set the BDT concentration as a constant; the CPFX release amount decreased withincrease of BDT in the gel when set CPFX concentration as a constant. BDT gel is a goodrelease material for CPFX, and their controlled-release behavior influenced by gelstabilization and microstructure.