Application Of Quantum Chemistry And Electrochemistry In Determination And Toxic Investigation Of Phenols In Environment

In environmental science,the determination of the concentration and the forms of phenols,the transport of phenols in organism,molecular chemistry active of phenols and the damage to biological active molecule, are important in controlling its damage to human being.This paper deal with these questions:(1)Density-functional theory(DFT)were performed for calculation of the theoretical spectrum and chemical activity of free radicals generated by benzoquinone and hydroquinone as well as the transition states,and the calculated spectrum were used for the assignment of the frequencies observed in the experimental IR spectrum.The calculated geometrical parameters,the predicted IR spectrum and chemical activity of free radicals and transition states were also compared with those of benzoquinone and hydroquinone.The reactive mechanisms of free radicals generated by benzoquinone and hydroquinone were also discussed using ab initio Hartree-Fork(HF)methods.(2)Geometric parameters,the vibrational frequencies and thermochemical values of benzoquinone and hydroquinone were computed by both ab initio calculation(HF)and density functional theory(B3LYP) methods with the 6-31G(d)and cc-PVDZ basis sets.The calculated frequencies of benzoquinone and hydroquinone were used for the assignment of the IR frequencies observed in the experimental IR spectrum. Cyclic voltammetry with a gold electrode of hydroquinone solutions in phosphate buffers at pH 7.00 showed that standard electrode potential of half reaction for benzoquinone and hydroquinone was 0.745 V.Standard electrode potential of half reaction for benzoquinone and hydroquinone was calculated using the sum of electronic and thermal free energies,enthalpies of sublimation and energies of solvation of benzoquinone and hydroquinone. The results showed that standard electrode potential of half reaction for benzoquinone and hydroquinone is 0.639V at B3LYP/6-31G(d)level, 0.587V at HF/6-31G(d)level and 0.796V at B3LYP/cc-PVDZ level. Geometric parameters,the vibrational frequencies and thermochemical values of o-benzoquinone,p-benzoquinone,pyrocatechol and p-hydroquinone were computed using ab initio calculation(HF)and density functional theory(DFT)with the 6-31G(d)and 6-31G(d,p)basis sets, respectively.Cyclic voltammetry with a gold electrode of pyrocatechol solutions in phosphate buffers at pH 7.30 showed that the standard electrode potential of half reaction for o-benzoquinone and pyrocatechol is 0.813V. The standard electrode potential of half reaction for o-benzoquinone and pyrocatechoI with a p-benzoquinone,H⁺/p-Hydroquinone reference electrode,using the solvation energies and the sum of electronic and thermal free energies of o-benzoquinone and pyrocatechol,is 0.727V at HF/6-31G(d),0.787V at HF/6-31G(d,p),0.745V at B3LYP/6-31G(d) and 0.754V at B3LYP/6-31G(d,p),respectively,and is consistent with the experimental one.Geometric parameters,vibrational frequencies and thermochemical values of p-aquinonimine and p-aminophenol were computed by ab initio calculation(HF)and density functional theory(DFT) with the 6-31G(d,p)basis sets.Cyclic voltammetry with a gold electrode of p-aminophenol solutions in phosphate buffers at pH 7.30 showed that standard electrode potential of half reaction for p-aquinonimine and p-aminophenol is 0.728V.Standard electrode potential of half reaction for p-aquinonimine and p-aminophenol were calculated using the free energies and solvation energies of p-aquinonimine,p-aminophenol,p-benzoquinone and hydroquinone.The results show that standard electrode potential of half reaction for p-aquinonimine and p-aminophenol is 0.743V at B3LYP/6-31G (d,p)level and 0.755V at HF/6-31G(d,p)level,respectively, indicating that computed standard electrode potential at B3LYP/6-31G(d,p) and HF/6-31G(d,p)level is consonant with experimental one.The balance constant of the batteries corresponding to phenols and oxygen was calculated,and the theoretical distribution of p-aquinonimine/ p-aminophenol,p-benzoquinone/p-hydroquinone and o-benzoquinone/ pyrocatechol in water and blood of human being were also discussed.(3)Electrochemical behavior of p-aminophenol,hydroquinone and pyrocatechol at bare gold electrode in 0.05mol/L Na₂HPO₄-0.05mol/L NaH₂PO₄-0.10mol/L NaCl buffer solution(pH=7.30)was studied by cyclic voltammetric(CV),and the CV of phenols binding albumin bovine was also studied,indicating that the oxidation peak shifts posstive,the reduction peak shifts negative and their current decreases.The interaction betwwen albumin bovine among phenols ascribes to the hydrogen bond between hydroxy of phenols and residue of amino acid.This interaction could be divided into two parts:one is specific,another is non-specific. According to the saturation of phenols binding albumin bovine,the specific binding number of p-hydroquinone,p-benzoquionone, p-aminophenol,p-aminoquine,pyrocatechol and o-benzoquionone binding albumin bovine is 26:1,26:1,5:1,5:1,22:1 and 8:1, respectively,indicating that the interaction between albumin bovine among p-hydroquinone,p-benzoquionone and pyrocatechol is stronger than those between albumin bovine among p-aminophenol,p-aminoquine and o-benzoquionone.The electrochemistry behavior was also discussed using quantum chemistry.(4)The interaction between hydroquinones and deoxgribonucleic acid in pH 7.42 sodium phosphate buffer solution using ultraviolet-visble spectrophotometry,fluorescence spectrophotometry,cyclic voltammetry and opening DNA chain technology was investigated,the experimental results show that peaks and the intension of absorption and fluorescence spectra of hydroquinones and deoxgribonucleic acid change obviously in opening DNA chain process(100℃),and the absorption peaks and fluorescence peak shift to red band,indicating that new copmpound form in the interaction between hydroquinones and deoxgribonucleic acid at 100℃.To study on the interaction between p-hydroquinones and DNA the electrochemical behavior of hydroquinones at the nucleoside triphosphate and double chain DNA modified gold electrode in 0.05mol/L Na₂HPO₄ -0.05mol/L NaH₂PO₄-0.10mol/L NaCl buffer solution(pH=7.30)has been investigated.The oxidation potential of hydroquinones at at nucleoside triphosphate shifted to positive,and the reduction potential of p-benzoquionone shifted to negative,the current of both ruduction and oxidation peak decreased.The simlar results of hydroquinones at DNA modified gold electrode were found.The study of quantum chemistry indicated that the interaction between hydroquinones and DNA bases mainly ascribes to theirП-Пbonding.The oxidation peak of hydroquinones damaging adenine,cytosine and guanine were obersered. The DNA adducts were determined with cyclic voltammetry and square-wave voltammetry.(5)The geometries of phenol,hydroquinone,resorcinol,catechol, o-aminophenol,p-nitrophenol and 2,4,6-trinitrophenol were optimized using ab initio Hartree-Fock(HF)and density-functional theory(DFT) B3LYP method at 6-31G(d)level.The molecular radius and Molar volume in gas,the dipole moment in gas,water and methanol,Sum of negative Mülliken charges and Frontier Molecular Orbital(LUMO and HOMO) were also calculated at the same level.Seven phenols were separated by inversed-phase high performance liquid chromatography(HPLC).The correlation coefficient between retention time and molecular radius or Molar volume,the dipole moment,the sum of negative Mülliken charges and LUMO using multiple linear regression(MLR)are calculated.The results show that the retention time of solute in HPLC were controlled by molecular radius or Molar volume,the dipole moment,the sum of negative Mülliken charges and LUMO(the interaction between solution and solute).