Understanding the Role of Citric Acid on the Crystallization Pathways of Calcium Oxalate Hydrates

Abstract

The precipitation of calcium oxalate can be either grown into structural support in plants or precipitated as stones in human kidneys. Previously, citrate, an effective inhibitor for oxalate stone formation, was suggested to alter the crystallization pathway of calcium oxalate and enhance the formation of less stable calcium oxalate trihydrate; however, the underlying mechanism is unknown. Herein we investigated the role of citric acid on crystallization pathways of calcium oxalate hydrates and the effect of supersaturation. It was found that the presence of citric acid can modulate the water content of amorphous nucleated precipitates by TEM and XRD and hence promote the formation of different calcium oxalate hydrates. The remaining water content in amorphous precipitates depends upon the amount of citric acid employed. FTIR and XRD analyses further reveal the extreme structural similarities between amorphous precipitates and the resultant hydrates. Additionally, the role of citric acid on crystallization pathways could be completely changed by supersaturation of calcium oxalate. High supersaturation dominated by homogeneous nucleation can diminish or even invalidate citric acid roles. The findings highlight the interplay of roles between additives and supersaturations, and could improve current understandings on the formation mechanism of oxalate stone.

Morphology of yellow passion fruit seedlings submitted to triazole induced growth inhibition

“…Calcium oxalate crystals occur naturally in many species. Functions of calcium oxalate include calcium regulation/sequestration, ion balance regulation, detoxification of high levels of heavy metals and oxalic acid, enhancement of absorption/reflection of incident radiation, protection from herbivory, and release of carbon when stomatal conductance is low (Li et al, 2019). When stomatal conductance is low, the number of druses was found to increase in the phloem of Passiflora edulis, Passiflora setacea, Passiflora gibertii and Passiflora cincinatta (Souza et al, 2018).…”

“…PBZ indirectly impacts ascorbic acid biosynthesis, thereby increasing the formation of calcium oxalate crystals (druses) in stem tissues (Soumya;Kumar;Pal, 2017). Ascorbic acid is thought to be the main precursor of calcium oxalate in idioblasts (Li et al, 2019).…”

Stabilization of Calcium Oxalate Precursors during the Pre- and Post-Nucleation Stages with Poly(acrylic acid)

“…Recent experimental evidence suggests that the nucleation of CaOx occurs via a non-classical crystallization (NCC) pathway, which involves the bonding of calcium (Ca 2+ ) and oxalate (C 2 O 4 2− ) ions into multi-ion associates known as pre-nucleation clusters (PNC), which can evolve into a condensed phase, amorphous CaOx (ACO), which later on gives rise to the different types of crystalline forms of CaOx [ 13 , 14 , 15 ]. The foregoing path involves a multi-step crystallization process, unlike classical crystallization (CC), that predicts that at a sufficiently high supersaturation, nucleation of a stable crystalline seed will occur which will continue to grow via incorporation of growth units (ions or molecules).…”

Effect of avocado (persea gratissima) leaf extract on calcium oxalate crystallization

“…The most stable form under normal atmospheric conditions is calcium oxalate monohydrate. Specific solution conditions (e.g., supersaturation) and temperatures are required for the other forms [4][5][6] . Calcium oxalate monohydrate crystals are known to be the main component of stone formation in the urinary tract and kidneys.…”