The Influence of pH and Temperature on the Stability of N-[(Piperidine)methylene]daunorubicin Hydrochloride and a Comparison of the Stability of Daunorubicin and Its Four New Amidine Derivatives in Aqueous Solutions

Table 1

Kinetic and thermodynamic parameters for the degradation of PPD in aqueous solutions.

𝑇(K)	𝑘±Δ𝑘 (s^−1)	Statistical evaluation; ln 𝑘𝑖=𝑓(1/𝑇)	Thermodynamic parameters
313	(1.17±0.05)⋅10^−3	𝑟=−0.999; 𝑎=−13220±1010; 𝑏=35.5±3.1	𝐸𝑎=109.9±8.4  (kJ·mol^−1); Δ𝐻^≠=107.5±8.4  (kJ·mol^−1); Δ𝑆^≠=50.2±25.6  (J·K^−1·mol^−1)
323	(4.40±0.03)⋅10^−3
333	(1.39±0.08)⋅10^−2
343	(4.84±0.03)⋅10^−2
303	1.19⋅10^−4	𝑟=−0.850; 𝑎=−3440±9162; 𝑏=2.64±30.1	𝐸𝑎=28.6±76.2 (kJ·mol^−1); Δ𝐻^≠=26.2±76.2  (kJ·mol^−1); Δ𝑆^≠=−222.8±250.2 (J·K^−1·mol^−1)
308	2.01⋅10^−4
313	2.21⋅10^−4
303	2.66⋅10^−4	𝑟=−0.999; 𝑎=−9555±1065; 𝑏=23.8±3.5	𝐸𝑎=79.4±8.9 (kJ·mol^−1); Δ𝐻^≠=81.9±8.9 (kJ·mol^−1); Δ𝑆^≠=−45.9±29.0 (J·K^−1·mol^−1)
308	4.36⋅10^−4
313	1.23⋅10^−3
303	0.970⋅10^−3	𝑟=−0.999; 𝑎=−7509±690; 𝑏=18.3±2.3	𝐸𝑎=62.4±5.7 (kJ·mol^−1); Δ𝐻^≠=60.0±5.7  (kJ·mol^−1); Δ𝑆^≠=−92.9±18.8 (J·K^−1·mol^−1)
308	1.50⋅10^−3
313	2.26⋅10^−3
318	3.23⋅10^−3

Δ𝐻^≠and Δ𝑆^≠were calculated for 298 K. 𝐸_𝑎=−𝑎𝑅(Jmol⁻¹);Δ𝐻^≠=𝐸_𝑎−RT(Jmol⁻¹);Δ𝑆^≠=𝑅(ln𝐴−ln(𝑘_𝐵𝑇)/ℎ (J K⁻¹ mol⁻¹), where 𝑘_𝐵: Boltzmann constant (1.3807 10⁻²³ J K⁻¹); ℎ = Planck constant (6.626 10⁻³⁴ J s); 𝑅 = universal gas constant (8.314 J K⁻¹ mol⁻¹); 𝑇: temperature in K; 𝑎: vectorial coefficient of the Arrhenius relationship; 𝐴: frequency coefficient.