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Effects of Solvation of 2-Methylpyridine and 2,6-Dimethylpyridine in Dilute Solutions in Water and Methanol οn the Limiting Partial Molar Compressibility and Volume

100%

Czech B., Marczak W.

Acta Physica Polonica A

2008

vol. 114

issue 6A

A-45-A-50

The limiting partial molar volumes and isentropic compressibilities of 2-methylpyridine and 2,6-dimethylpyridine in aqueous and methanolic solutions were calculated from the densities and speeds of sound at 293.15 and 298.15 K. All the limiting functions are smaller than the respective functions for the pure amines, due to the hydrogen bonds O-H... N between the amine molecules and those of water or methanol. The standard functions of transfer of the amines from methanol to water are negative which results from different nature of interactions in the aqueous and methanolic solutions. Most probably, the hydrophobic effect contributes to the limiting partial volumes and compressibilities of the amines diluted in water. That makes them smaller than the respective functions for the amines in methanol.

Complexes of Silver with Histidine and Imidazole Investigated by the Calorimetric and Potentiometric Methods

81%

Czoik R., Heintz A., John E., Marczak W.

Acta Physica Polonica A

2008

vol. 114

issue 6A

A-51-A-56

The stability constants and enthalpies of formation of silver (I) complexes with histidine and imidazole were determined. Two types of complexes were found: AgL⁺ and AgL⁺₂. The second is much more stable that is evidenced by the higher stability constants and enthalpies of formation. For the two systems, the respective constants and enthalpies are very close one to another that suggests similar complexation mechanisms. Most probably, the linear complexes through the N-3 pyridinic atoms are being formed. The calorimetric and potentiometric methods gave virtually the same results for the system silver + imidazole. However, the potentiometric method failed for the histidine system. The molecule of histidine has three protonation spots, two of these probably do not take part in the complexation but their protonation equilibria may shift upon joining the ions of silver and influence the pH of the system in that way.

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2 Acta Physica Polonica A

2 2008

2 Marczak W.

1 Czech B.

1 Czoik R.

1 Heintz A.

1 John E.

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Effects of Solvation of 2-Methylpyridine and 2,6-Dimethylpyridine in Dilute Solutions in Water and Methanol οn the Limiting Partial Molar Compressibility and Volume

Complexes of Silver with Histidine and Imidazole Investigated by the Calorimetric and Potentiometric Methods