Catalytic Sensing Of TACN-Based Coordination Polymers

Enzymes are extremely important to life.Many chemical reactions in human body are triggered by enzymes playing as the role of catalysts.Therefore,the related studies of enzymes have been attracted wide attentions.In analytical chemistry,there are three main ways to improve analytical sensitivity through signal amplification:(?)catalysis reactions;(?)multivalent interactions;(?)the allosteric effect of biomolecules.The first example of introducing catalysis reaction into analytical chemistry was enzyme-linked immunosorbent assay.However,due to some shortcomings of natural enzymes,such as harsh storage conditions,the drawback that the activity is easily affected by external conditions,and hardly purified,developing artificially enzymatic mimics has become to particularly important.For the cleavage reactions of phosphoesters,there are four kinds of mimics:(?)mononuclear/binuclear or polynuclears complexes;(?)dendrimers;(?)micelles/vesicles;(?)metal nanoparticles.Although the emergences of these mimics have greatly promoted the development of artificial enzymatic mimics,there are many disadvantages,for example:(?)the catalytic effect of mononuclear/binuclear or polynuclear complexes is poor due to the absence of cooperation;(?)the synthesis of dendrimers is much more challenge;(?)micelles/vesicles are instable;(?)the preparation of metal nanoparticles(1.8 nm)is troublesome and not easy to be effectively stored.Therefore,developing a novel kind of phosphate hydrolytic enzymatic mimics which are easy to be stored,stable and highly efficient in catalysis is certainly guiding significance for further establishing a catalytic sensing system with signal amplification.In this thesis,a series of thiol molecules with a 1,4,7-triazacyclononane group(TACN)with various aliphatic chain lengths were synthesized(HS-Cn-TACN;n=5,7,9,11,14,16,20).By employing Ag+ions and-SR to form…Ag-S(R)-Ag-S(R)…coordination polymers,and the coordination interaction between Zn2+ ion and terminated TACN group in side chains of the polymeric skeleton to in situ generate novel multivalent sites aggregates.The coordination polymers were constructed in situ by two steps(first mixing Ag+ ion and HS-Cn-TACN to form coordination polymers,then introducing Zn2+ion to coordinate with terminated TACN group).Further research showed that the polymer systems could effectively catalyze the hydrolysis of phosphate with the commonly used RNA analog 2-hydroxypropyl-4-nitrophenol phosphate diester(HPNP)as the substrate.Therefore,a novel kind of in-situ forming metal coordination polymeric enzymatic mimics has been successfully developed.The main researches were carried out as follows:(1)A series of thiols with various aliphatic chain lengths and terminated TACN group were synthesized by four steps,started from dibromoalkanes with various aliphatic chain lengths and TACN(HS-Cn-TACN;n=5,7,9,11,14,16,20).Then,Ag-S-Cn-TACN metal coordination polymers were formed in-situ by mixing Ag+ions and HS-Cn-TACN with molar ratio of 1:1.After that,Zn2+ions were further introduced to coordinate with the terminated TACN group in the side chain of the Ag-(S-Cn-TACN)polymeric skeleton to form Ag-(S-Cn-TACN)-Zn2+systems.It is found that,the polymeric systems have good catalytic activity for the hydrolytic reaction of HPNP,and the catalytic activity was related to the aliphatic chain lengths of thiols.Furthermore,it was also found that,Ag-(S-Cn-TACN)-Zn2+coordination polymers followed the traditional Michaelis Menten equation to catalyze the cleavage reaction of HPNP,indicated that it has enzyme-like catalytic activity,similar to phosphate hydrolase.Therefore,a novel kind of highly efficient and in-situ forming artificial enzymatic mimics towards phosphate hydrolase have been successfully developed in this work.(2)On the basis of the study of Ag-(S-Cn-TACN)-Zn2+coordination polymers,and considering that these polymers bear side chains terminated by TACN groups with various aliphatic chain lengths,tetrastyrene(TPE)was introduced to investigate the effect of side chain length on the fluorescence response.Thus,a sensing system could be employed to probe the hydrophobicity.In addition,considering the structural similarity between HPNP and organophosphates,acetylcholinesterase(AChE)was introduced to this catalytic reaction,thus a catalytic sensing platform for AChE activity could be constructed.