The stability constants of the ternary M(Bic)(Bzim)+ complexes, where M2+ = Cu2+, Ni2+ or Zn2+, Bic- = the anion of N, N-bis(2-hydroxyethyl) glycine and Bzim = benzimidazole, were determined by potentiometric pH titra...The stability constants of the ternary M(Bic)(Bzim)+ complexes, where M2+ = Cu2+, Ni2+ or Zn2+, Bic- = the anion of N, N-bis(2-hydroxyethyl) glycine and Bzim = benzimidazole, were determined by potentiometric pH titration in aqueous solution. One of them (M2+ = Cu2+) was also separately determined by spectrophotometry. The results show that these ternary complexes are stabler than expected on statistical grounds. The enhanced stability of the ternary M(Bic) (Bzim)+ complexes is attributed to the πA-πB cooperative effect between Bic- and benzimidazole. Besides, compared with Cu(Bic) (Bzim)+ and Ni(Bic) (Bzim)+, the ternary Zn(Bic) (Bzim)+ complex has relatively high stability. The crystal structure of [Cu(Bic)(Bzim)]ClO4 was determined by single crystal X-ray diffraction techniques. The copper atom has a trigonal-bipyramidal geometry, the basal plane is formed by an oxygen atom of the carboxylato group and two hydroxyl oxygen atoms, the apical position is occupied by a nitrogen atom of Bic- and a nitrogen atom of benzimidazole. The molecular structure of Cu(Bic) (Bzim)+ in aqueous solution is different from that in the crystalline state. The results of ESR and electronic spectra show that the structure of this complex is octahedron in aqueous solution.展开更多
This paper reports the results for the pH of three buffer solutions free of chloride ion. The remaining six buffer solutions have saline media of the ionic strength I = 0.16 mol.kg-1, matching closely to that of the p...This paper reports the results for the pH of three buffer solutions free of chloride ion. The remaining six buffer solutions have saline media of the ionic strength I = 0.16 mol.kg-1, matching closely to that of the physiological sample. Conventional paH values for the three buffer solutions without the chloride ion and six buffer solutions with the chloride ion at I = 0.16 mol.kg-1 from 5°C to 55°C have been calculated. The operational pH values for five buffer solutions at 5°C and 55°C have been determined based on the difference in the values of the liquid junction potentials between the blood phosphate standard and the experimental buffer solutions. Five of these buffers are recommended as standards for the physiological pH range 7.5 to 8.5.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No. 29871036)the Natural Science Foundation of Guangdong Province (Grant No. 97021)the State Key Laboratory of Coordination Chemistry of Nanjing University
文摘The stability constants of the ternary M(Bic)(Bzim)+ complexes, where M2+ = Cu2+, Ni2+ or Zn2+, Bic- = the anion of N, N-bis(2-hydroxyethyl) glycine and Bzim = benzimidazole, were determined by potentiometric pH titration in aqueous solution. One of them (M2+ = Cu2+) was also separately determined by spectrophotometry. The results show that these ternary complexes are stabler than expected on statistical grounds. The enhanced stability of the ternary M(Bic) (Bzim)+ complexes is attributed to the πA-πB cooperative effect between Bic- and benzimidazole. Besides, compared with Cu(Bic) (Bzim)+ and Ni(Bic) (Bzim)+, the ternary Zn(Bic) (Bzim)+ complex has relatively high stability. The crystal structure of [Cu(Bic)(Bzim)]ClO4 was determined by single crystal X-ray diffraction techniques. The copper atom has a trigonal-bipyramidal geometry, the basal plane is formed by an oxygen atom of the carboxylato group and two hydroxyl oxygen atoms, the apical position is occupied by a nitrogen atom of Bic- and a nitrogen atom of benzimidazole. The molecular structure of Cu(Bic) (Bzim)+ in aqueous solution is different from that in the crystalline state. The results of ESR and electronic spectra show that the structure of this complex is octahedron in aqueous solution.
文摘This paper reports the results for the pH of three buffer solutions free of chloride ion. The remaining six buffer solutions have saline media of the ionic strength I = 0.16 mol.kg-1, matching closely to that of the physiological sample. Conventional paH values for the three buffer solutions without the chloride ion and six buffer solutions with the chloride ion at I = 0.16 mol.kg-1 from 5°C to 55°C have been calculated. The operational pH values for five buffer solutions at 5°C and 55°C have been determined based on the difference in the values of the liquid junction potentials between the blood phosphate standard and the experimental buffer solutions. Five of these buffers are recommended as standards for the physiological pH range 7.5 to 8.5.
