Mechanistic Pathways for the Molecular Step Growth of Calcium Oxalate Monohydrate Crystal Revealed by In Situ Liquid-Phase Atomic Force Microscopy

Abstract

Calcium oxalate monohydrate (COM) crystal is the most common crystalline component of human kidney stones. The molecular-scale inhibitory mechanisms of COM crystal growth by urinary biomolecules such as citrate and osteopontin adsorbed onto the crystal surface are now well understood. However, the pathways by which dissolved calcium and oxalate ions are incorporated into the molecular step of the COM crystal surface, leading to COM crystal growtha prerequisite to be elucidated for developing effective therapeutics to inhibit COM stonesremain unknown. Here, using in situ liquid-phase atomic microscopy along with a step kinetic model, we reveal the pathways of the calcium and oxalate ions into the COM molecular step via the growth speed analysis of the molecular steps with respect to their step width at the nanoscale. Our results show that, primarily, the ions are adsorbed onto the terrace of the crystal surface from the solutionthe rate-controlling stage for the molecular step growth, i.e., COM crystal growthand then diffuse over it and are eventually incorporated into the steps. This primary pathway of the ions is unaffected by the model peptide D-Asp6 adsorbed on the COM crystal surface, suggesting that urinary biomolecules will not alter the pathway. These new findings rendering an essential understanding of the fundamental growth mechanism of COM crystal at the nanoscale provide crucial insights beneficial to the development of effective therapeutics for COM kidney stones.

Classical Spiral Growth Mechanism of Azilsartan Form I Revealed by In Situ Atomic Force Microscopy

“…This indicates that the molecular exchange between terraces and steps is more rapid than that between solutions and terraces. The rate-limiting stage for AZ step growth is the adsorption of AZ molecules from solutions onto terraces . All of these parameters are summarized in Table .…”

“…The rate-limiting stage for AZ step growth is the adsorption of AZ molecules from solutions onto terraces. 65 All of these parameters are summarized in Table 1.…”

In Situ Liquid-Phase AFM Observation of the Molecular Step Spiral Generation on the (1−01) Surface of Calcium Oxalate Monohydrate Crystal

“…Many studies on COM crystals, the main mineral crystal composing the calcium stones, employing isotopic methods [6] and tools like scanning electron microscopy [7,8], fluorescence microscopy [8,9], and in situ liquid-phase atomic force microscopy (AFM) [10][11][12][13][14][15][16][17][18][19][20][21], have been conducted to understand the effect of associate ion, Mg 2+ [6,19] and biomolecules (or artificial agents [16,17,19,20]) such as citric acid [11,13,14,22] and osteopontin [11,23] on the COM formation at various supersaturation and suggested the inhibitory mechanisms such as chelation of oxalate ions leading to increased solubility of calcium oxalate [6] and face-specific binding of the biomolecules (or artificial agents) to the growing molecular steps on crystal faces [11][12][13][14][15][16][17][18][19][20][21].…”

Natural inhibitors from earthworms for the crystallization of calcium oxalate monohydrate

“…6 The regulation of the mineralization by modifiers essentially alters the thermodynamics and dynamics of the nucleation and growth of crystals, thereby affecting the chemical and physical properties of crystals and aggregates. [7][8][9][10][11][12][13] Nature provides many examples of such processes, including modifications of minerals 14 and biological crystals. 22,23 Macromolecules, especially proteins, are the main regulators of the mineralization process in organisms.…”

“…3 Macromolecular recognition directs calcium ions to coccolith mineralization sites. [10][11][12] Therefore, the synthesis of multifunctional hybrid materials often draws inspiration from nature through the use of protein, peptides and other organic molecules for modulating crystal growth. 11,24,25 In fact, exploring how modifiers affect the crystal growth kinetics and morphology and how the solution environment changes the free energy landscape of the mineral surface is vitally important for establishing a model that can fully describe the growth of biological minerals.…”