kinetic and thermodynamic aspects of phosphate diester hydrolysis in alkaline solutions: the role of non-leaving groups

Alkaline hydrolysis of phosphate diester compounds with a common leaving group (lg) and varying non-leaving groups (nlg) was investigated. the nitrophenyl group was employed as a leaving group due to its favorable leaving group properties, significant absorbance for reaction monitoring, and selective cleavage of the phosphorus-oxygen bond, which is relevant for dna and rna degradation. reactions were conducted under pseudo first-order conditions in naoh solutions 70 °c. in addition, the alkaline hydrolysis was studied using a 1m naoh solution at different temperatures (50–80 °c), ph (12-14) levels, and viscosities (with 0% - 40% glycerol). reaction progress was continuously monitored by measuring the absorbance increase of the 4-nitrophenolate ion at λ = 400 nm. the rate constant (kobs) was determined by fitting the data to a first-order equation. the results demonstrate kobs increased with higher naoh concentration, temperature, ph, and solution viscosity, except for nppnpp. investigation of the effect of the non-leaving group’s pka revealed slight sensitivity of the hydrolysis reaction with βnlg = -0.12. thermodynamic parameters were determined and the values were as follows: ∆h = 48.8 kj.mol-1, ∆s = -171.6 j.mol-1.k-1, ∆g = 99.9 kj.mol-1 for bpnpp; ∆h = 64.9 kj.mol-1, ∆s = -127.1 j.mol-1.k-1, ∆g = 102.8 kj.mol-1 for pypnpp; ∆h = 86.3 kj.mol-1, ∆s = -76.7 j.mol-1.k-1, ∆g = 109.2 kj.mol-1 for mpnpp, and ∆h = 63.7 kj.mol-1, ∆s = -152 j.mol-1.k-1, and ∆g = 109 k kj.mol-1 for nppnpp. all four hydrolysis processes have positive ∆g values, which means they are non-spontaneous and require external energy to proceed.