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

Abstract

Calcium oxalate monohydrate (COM) crystal is the major crystalline component of human kidney stones. Its growth event at the nanometer and micrometer scales, i.e., the growth of the COM molecular steps generated from the dislocation outcrop on the crystal surface and its inhibition by associated acidic organic molecules such as citrate, is now well understood by studies conducted using in situ liquid-phase atomic force microscopy (AFM). Yet, the detailed assessment of the evolution of the COM molecular steps at the dislocation outcrop has been poorly conducted. Herein, in situ liquid-phase AFM was used to primarily investigate how those COM molecular steps are generated on a COM broadest crystal surface (1−01) and influenced by a model acidic peptide, L-aspartic acid 6mer (L-Asp6) adsorbed onto the emerging steps and terraces on the surface. Like many other mineral crystals, a segment of the pseudo-triangle-shaped step spiral, in the process of its birth from the dislocation outcrop, starts to move after reaching the critical step length. When the budding step spiral got adsorption of L-Asp6 to it, it appeared rather with ellipse-like hexagonal morphology—which is reflected in the bulk crystal morphology—implying changes in orientation-dependent step edge energy and much-delayed spiral generation time.