Designing and estimating antioxidant properties of some lubricant additives via QSPR and MD methodologies

Abstract

Quantitative structural properties relationship (QSPR) was used as an investigational tool to design new lubricant antioxidant additives with better properties that could replace the long-used multipurpose lubricant additive, Zinc dipropyl dithiophosphate (ZDDP). Also, molecular dynamics (MD) investigational technique was carried out to access the dynamic binding strengths of designed additives on simulated coated diamond-like carbon (DLC) and steel surfaces. Four new antioxidant lubricant additives with better antioxidant lubricant properties (mg KOH/g oil) were successfully designed. From the MD study, all the designed additives were found to dynamically bind to steel simulated coated sliding surface with energies of -1054.89, -1081.82, -1368.21 and -1222.8 kcal/mole, while they also show dynamic binding energies of -53.372, -51.141, -55.122 and -50.083 kcal/mole on DLC simulated coated surface at elevated temperatures. One of the four designed additives 4-(3-ammonio-4-hydroxyphenyl)-5-cyano-1,4-dihydropyrano[2,3-c]pyrazole-3,6-diaminium with lubricant antioxidant property of 0.003263 mg KOH/g oil was found to be better than other co-lubricant antioxidant additives in-term of property and was also better than the one reported by another investigator. Also, molecular dynamics (MD) investigation revealed that all the four designed antioxidant lubricant additives were bound better to the steel simulated surface than the DLC surface. This investigation successfully designed four new lubricant additives with better lubricant antioxidant properties that do not contain zinc and phosphorus and could be used by industrialists to replace the multipurpose lubricant additive, ZDDP which contain zinc that restricts the function of catalytic converter and phosphorus that produces and deposit ashes in the car exhaust pipe.