Influence Of Dissolved CO₂,N₂ And O₂ Gas Molecules In Aqueous Solution On The Water-Exchange Reactions Of Hydrated Aluminum Cations:A Density Functional Theory Study

Aluminum(Al)is an active component in diverse chemical reactions and biological process in environment.Investigations on different configurations and characteristics of Al have always been the priority subjects of environmental chemistry and geochemistry.The water-exchange reactions of hydrated Al cations between the first hydration sphere and the bulk water is essential for insight into the hydrolysis-polymerization behavior and complexation mechanism of hydrated Al cations in aqueous solution.There are many studies on the water-exchange reactions of hydrated Al cations in the aqueous solution.However,it is still difficult to completely and accurately describe the formation and water-exchange reactions of hydrated Al cations at the molecular level experimentally.Quantum chemical calculations offer a new route for solving the problems encountered in experiments.The problems existing in the theoretical investigations on the water-exchange reactions of hydration Al cations are as follows:(1)the H-bonds between the first and the second hydration spheres of Al3+ are non-negligible,as well as the solvent-solvent interactions.How to simulate the solvent effect for the water-exchange reaction of hydrated Al cations is still a matter of lively debate;(2)gases are widely dissolved in the natural water,soil and blood,having significant effects on the metabolism of animals and plants.However,researches have ignored the influence of dissolved gas molecules in aqueous solution when conducted the investigations on the water-exchange reaction of hydration Al cations in the past;(3)access to the computational steps taken to process data is important,however,reporting of and access to such information is not routine in the scholarly literature.In this dissertation,the water-exchange reactions of hydrated Al cations in aqueous solution are studied systematically.The configuration characteristics and water-exchange reactions of Al-maltolate complexes are also studies to investigate their toxicity mechanism.There are four chapters as follows:1.Investigation of the solvent effects for Water-exchange reactions of Al(H2O)63+ by quantum chemical cluster models-density functional theory method.Based on the four models(gas phase(GP),polarizable continuum model(GP-PCM),supermolecule model(GP-SM)and supermolecule-polarizable continuum model(GP-SM-PCM)),we systematically conducted the following investigations using quantum chemical cluster models-density functional theory.The water-exchange reaction of Al(H2O)63+ was simulated at the level of B3LYP/6-311+G(d,p),and the single-point energies were calculated using MP2 method.Taking zero-point energies,thermal corrections and entropies into consideration,the activation energy barries and water-exchange rate constant(kex)were calculated.The log kex for water-exchange reactions of Al(H2O)63+ with GP-SM//MP2-PCM and GP-SM-PCM//MP2-PCM models were similar and consistent with available literature values.This indicates that the GP-SM//MP2-PCM model could simulate the water-exchange reaction of Al(H2O)63+satisfactorily.2.Influence of dissolved CO2,N2 and O2 gas molecules in aqueous solution on the water-exchange reactions of hydrated Al cations:a density functional theory study.The influences of dissolved CO2,N2 and O2 gas molecules in aqueous solution on the water-exchange reactions of hydrated Al cations were investigated using quantum chemical calculation method of the combination of density functional theory-cluster models.The following studies were carried out at the level of B3LYP/6-311+G(d,p):(1)The reactants,transition states and products for water-exchange reactions of hydrated Al cations with CO2,N2,and O2 molecules in the inner sphere of A13+ were optimized and the thermodynamic parameters were calculated.The results indicate that CO2 and N2 in the inner sphere increase the activation Gibbs free energies for the water-exchange reactions of the cis and trans water molecules,while the 1O2 labilize the cis H2O and stabilize the trans H2O;(2)The impacts of CO2,N2,and O2 gas molecules in the outer sphere of A13+ on the water-exchange reactions of Al(H2O)63+ were explored,and the activation Gibbs free energies were found to increase upon replacing the surrounding solvent water molecule with a gas molecule;(3)The water-exchange reactions of Al(H2O)63+with CO2,N2,and O2 gas molecule dimers and trimers in the outer sphere were examined,and the results show that the differences among the activation Gibbs free energies for systems of gas molecule monomers,dimers and trimers could be ignored.However,the surface charges of gas clusters were found to change significantly due to the inductive effect of Al(H2O)63+.3.Investigation of the configuration characteristics and water-exchange reactions of aluminium(?)-maltolate complexes by density functional theory.The following studies were investigated using density functional theory:(1)The structures of 1:1/1:2/1:3 Al-maltolate complexes were optimized at the level of B3LYP/6-311+G(d,p).The microscopic properties,NPA charges and energies were obtained.The 1H and 27Al NMR chemical shifts,ultraviolet spectral data and infrared absorption of four isomers of Al(ma)3 were calculated.The calculation results showed that the values obtained with the GP-SM-PCM models were in good agreement with the experimental data available in the literatures,indicating that the models we employed were appropriate for Al-maltolate complexes;(2)The water-exchange reactions of Al-maltolate complexes were simulated at the same computational level.The logarithm of water-exchange rate constants(log kex)of three sites predicted using the "log kex-?Ga?" correlation were 2.4(Al(ma)(H2O)42+(cis to ma)),2.6(cis-Al(ma)2(H2O)2+(?))and 3.0(trans-Al(ma)2(H2O)2+(?))respectively.The results were consistent with available experimental values,indicating that the corresponding sites were active sites for water-exchange reactions;(3)The relationship between toxicity and speciation of Al-maltolate complexes was discussed.4.The introduction of density functional theory-cluster model and solutions to the calculation errors.Definitions of density functional theory,cluster model and four models(gas phase model,polarizable continuum model,supermolecule model and supermolecule-polarizable continuum model)are summarized.This chapter also gives the procedures for the calculations of thermodynamic parameters.The solutions to errors encountered in the calculations are summarized to provide the useful references for future research.