Formation of calcium oxalate nanoparticles in leaves: significant role of water content and age of leaves

Abstract

Calcium oxalate monohydrate (COM) was synthesized in the presence of leaves which act as a source of oxalate ions. Three different leaves, viz. Ficus religiosa (peepal in India), Heterophragma adenophyllum (Katsagon) and Spinacia oleracea Linn. (spinach) were used for the synthesis, which led to nanoparticles of COM of size 100–300 nm, 40–70 nm and 150–200 nm respectively. The particles are highly monodisperse, spherical and uniform in size as shown by TEM studies. The amount of COM formed varied significantly (35–80%) with the type of leaf used. The yield could be inversely correlated with the water content of the leaves; though water is essential for the formation of COM (dry leaves do not yield COM). Our studies show that the secretion of oxalate ions (to form COM) from the cells occurs even in leaves which have been removed from the living plants and the ability to secrete oxalate ions increases with the age of the leaf. The young leaves of F. religiosa do not show COM formation. In the presence of chelating agents (like citric acid) which can bind to Ca²⁺ ions, COM is absent, suggesting that the secretion of oxalate ions is prevented.