The research on formation enthalpy of phenanthroline monohydrate and its influence on the growth metabolism of E. coli by microcalorimetry

A precision rotating-bomb combustion calorimeter (thermistor of which was constructed in the laboratory) was calibrated using benzoic acid with purity of 99.999 %. The combustion energy of phenanthroline monohydrate (phen·H2O) at 298.15 K was determined to be Δc U m θ = −(5,757.45 ± 2.53) kJ mol−1. Then, the standard enthalpy of combustion and the standard enthalpy of formation of phen·H2O were calculated to be Δc H m θ = −(5,759.93 ± 2.53) kJ mol−1 and Δf H m θ = −(391.34 ± 2.98) kJ mo1−1, respectively. Particularly, the effect of phen·H2O on growth and metabolism of Escherichia coli (E. coli) was also determined by a TAM air isothermal calorimeter at 37 °C. The thermokinetic parameters, including maximum heat output power (P max), growth rate constant (κ), generation times (t G), inhibitive rate (I), and half inhibition concentration (C I,50), were obtained. The results showed that phen·H2O possessed the bi-directional biological effect and Hormesis effect, which stimulated the growth of E. coli at lower concentration, but inhibited the growth at higher concentration. The half inhibition concentration C I,50 of phen·H2O was found to be 7.31 mg L−1.