| In recent years,endocrine-disrupting chemicals(EDCs)have attracted much attention because of their harmful effect on human health and wildlife.Bisphenol A(BPA)is regarded as a representative EDCs since it is widely used in the manufacture of polycarbonate epoxy resins and flame retardants and as an additive in plastics.Many products can release BPA into the environment,such as baby bottles,reusable water bottles,food can walls,adhesives,artificial teeth and food packaging materials.Unfortunately,even very low doses of BPA have been demonstrated to do harm to wildlife and humans,leading to problems related to the breast,prostate,neurobehavioural systems and reproductive systems.Much effort has been made to establish a simple,effective,and highly sensitive method for monitoring BPA.Traditional detecting methods for BPA include HPLC,GC-MS/MS,fluorescence analysis and electrochemical detection.However,these detection methods possess the drawbacks of low sensitivity and poor selectivity,are time consuming,and require professional operators and expensive instruments.It is still a challenge to explore new techniques to detect BPA in situ with high sensitivity,selectivity,and efficiency.The molecular imprinting technique is a method to prepare molecular imprinting polymers(MIP)with highly specific recognition of a desired template molecule.MIP has high selectivity and can recognize the template molecule from a mixture thatincludes structurally analogous species.Owing to the peculiarity of the specific identification of molecular imprinting technique,the technique has been applied to the analysis and detection field of environment pollutants including BPA.The choice of the functional monomer interaction with the template molecule is a critical factor in determining the performance of MIP.The preparation of MIP involves self-assembly,polymerization,template extraction and template rebinding four steps.Therefore,from the perspective of the experiment,good performance of MIP is obtained based on a mountain of experimental work.But experimental process is subject to many factors,such as environment,conditions,time,etc.,and the cost of experiment are frequently considered.At present,the research method of theoretical calculation has been used in the field of molecular imprinting technique.Adopting the theoretical calculation method for study of molecular imprinting technique can avoid the flaws in the process of the experiment mentioned above.More importantly,theoretical research results can reveal the mechanism of MIP formation and the relationship between the properties and structure of the MIP systems.These theoretical research results can afford valuable guidance for designing and preparing MIPs.This thesis mainly adopts theoretical calculation methods to study the structure,properties and the imprinting mechanism of BPA molecularly imprinted complexes.In addition,from the perspective of thermodynamics the external conditions for preparation of molecularly imprinted complexes including temperature and solvent medium were investigated theoretically,and the corresponding results enhance the practical application value of this theoretical work.This should be the innovativepoint of this research work.The main research work and results were summarized as follows:In this thesis,using BPA as the template,2-vinylpyridine(2-Vpy,a),4-vinylpyridine(4-Vpy,b),methacrylic acid(MAA,c)and acrylamide(AM,d)as the functional monomers,the 1:1(1a,1b,1c,1d)and 1:2(2a,2b,2c,2d)molecularly imprinted complexes were investigated by quantum chemical calculations at the DFT/B3LYP/6-311++g(d,p)level.The optimized stable geometrical structures,electrostatic potential distribution,NBO Charge,vibrational and electronic absorption spectra,interaction energies and thermodynamic property were employed to investigate the interaction strength and the mechanism between BPA and different functional monomers.Through the analysis of electrostatic potential and charge distribution,it was found that the sites of oxygen and hydrogen of hydroxyl in BPA,the N in 4-Vpy and2-Vpy,the carbonyl oxygen and hydroxyl hydrogen in MAA,the carbonyl oxygen and amino hydrogen in AM all have strong electrostatic property,acting as the active sites in the formation of molecularly imprinted complexes.The molecularly imprinted complexes were formed from BPA and corresponding functional monomer through electrostatic attraction between the active sites.The geometrical structure optimization on the molecularly imprinted complexes revealed the distances between the active sites are in the range of 1.80-2.17 ?,which accord with the data of-O…H(O),-O … H(N),-N … H(O)distances reported in literatures.Upon forming the imprinting complex,the vibration spectra of functional groups near the active siteschanged somewhat due to the intermolecular interactions whether in BPA or the corresponding functional monomers.The most remarkable variation was that the strong O–H stretching vibration at 3453 cm-1 in isolated BPA was weakened and red-shifted by ca.230-420 cm-1 in the complexes,which was due to the formation of intermolecular hydrogen bond between hydroxyl hydrogen of BPA and the corresponding active site of the functional monomer.The electronic absorption spectra of the complexes were a simple superposition of those of BPA and corresponding functional monomers.The evaluated N…H(O),O…H(O)and O…H(N)interaction energies of 32-42 k J/mol in all the complexes were equivalent to those of typical hydrogen bonding interactions.In conclusion,the interaction between BPA and corresponding functional monomer in complexes is attributed to the hydrogen bonding interaction.The calculation results showed that the strength of interaction energies of all the complexes with different functional monomers is in the order of AM > MAA >4-Vpy > 2-Vpy,and the strongest one among them,the interaction energy between BPA and AM is about ca.42.0 k J/mol.So from the perspective of the interaction strength,AM is the most suitable functional monomer.Moreover the total interaction energies of the complexes significantly increased but the interaction energies between each pair of active sites in the complex slightly decreased when the ratio between BPA and corresponding functional monomer going from the 1:1 to the 1:2.Therefore,it can be concluded that a high ratio between BPA and functional monomers can increase the total interaction energy of the complexes but cannot enhance theinteraction strength between the action sites.The geometric structure,the interaction energy and the thermodynamic property data of all the complexes with the temperature controlled in the range of 293.15 to313.15 K and in the gas phase,toluene and methanol solvent were calculated.The results showed that mildly polar solvent media and normal temperature conditions were thermodynamically favourable for preparing molecular imprinting complexes. |
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