Step kinetics on monosodium urate monohydrate single crystal surfaces: an in situAFM study

Abstract

The deposition of monosodium urate (MSU) crystals in synovial fluid is a classic clinical symptom of the joint disease gout. In previous work (CrystEngComm, 2011, 13, 1111–1117), it was reported that crystal growth occurs by an island deposition mechanism in 2–10 mM urate solutions under simulated physiologic conditions (150 mM NaCl, 37 °C, pH = 7.4). The present work examines in greater detail the molecular-level growth occurring in the areas between deposited islands on two types of single crystal surfaces – (100) and (1–10) using in situ atomic force microscopy. The surface topography on both types of faces consisted of elementary (unit cell) steps and macrosteps (>45 nm) which showed significant quantifiable differences in their in-plane growth kinetics. All growing steps exhibited orientations corresponding to high Miller Index directions and showed a non-linear increase in lateral velocity over the supersaturation range σ = 2.5–3.4. Topographical imaging was additionally used to establish the preferred relative orientation of domains in these frequently twinned crystals.