Adhesion Properties of Uric Acid Crystal Surfaces

Abstract

Two key steps in kidney stone formation--crystal aggregation and attachment to renal tissues--depend on the surface adhesion properties of the crystalline components. Anhydrous uric acid (UA) is the most common organic crystalline phase found in human kidney stones. Using chemical force microscopy, the adhesion force between various functional groups and the largest (100) surface of UA single crystals was measured in both aqueous solution and model urine. Adhesion trends in the two solutions were identical, but were consistently lower in the latter. Changes in the solution ionic strength and pH were also found to affect the magnitude of the adhesion. UA surfaces showed the strongest adhesion to cationic functionalities, which is consistent with ionization of some surface uric acid molecules to urate. Although hydrogen-bonding and van der Waals interactions are usually considered to be dominant forces in the association between neutral organic compounds, this work demonstrates that electrostatic interactions can be important, particularly when dealing with weak acids under certain solution conditions.

Best Practices for Real-Time in Situ Atomic Force and Chemical Force Microscopy of Crystals

“…For example, adhesion forces on the largest crystal face of calcium oxalate monohydrate (COM) crystals, measured in solution, are significantly greater than those measured on the largest face of calcium oxalate dihydrate, explaining the higher propensity of COM crystals to form stones. − CFM experiments performed on l -cystine crystals demonstrated comparable surface adhesion of different habits and polymorphs of l -cystine crystals, thereby ruling out the possibility of aggravating stone formation by a shift in crystal morphology, further illustrating the practical utility of this methodology . CFM also was used to investigate the effects of common urinary constituents in l -cystine stone formation, and others have used CFM to study cholesterol monohydrate, uric acid and monosodium urate monohydrate crystals. − …”

Pyridinic and graphitic nitrogen-rich graphene for high-performance supercapacitors and metal-free bifunctional electrocatalysts for ORR and OER

“…Uric acid has a high nitrogen content ($33 wt%), and its crystals can adhere to surfaces bearing various organic functionalities, and via multiple types of forces (electrostatic interactions, hydrogen bonding and/or van der Waals interactions), without the aid of surfactants. 57 These properties allowed the copyrolysis of graphene oxide and uric acid to produce a nitrogendoped reduced graphene oxide (rGO) with nitrogen atoms in all of the possible congurations in the graphitic lattice, a high total nitrogen content with a high ratio of pyridinic N and graphitic N and a high surface area aer pyrolysis. As a result, the N-doped graphene had both high capacitance and bifunctional electrocatalytic activity towards oxygen reduction and evolution.…”

Nanoarchitectured Nitrogen-Doped Graphene/Carbon Nanotube as High Performance Electrodes for Solid State Supercapacitors, Capacitive Deionization, Li-Ion Battery, and Metal-Free Bifunctional Electrocatalysis

“…Uric acid, because of its good adhesive properties, can form hydrogen bonds with carboxyl groups with an adhesion force of 1.62 nN. 44 During the sonication and stirring at 80 °C, because of its excellent surface attachment properties, the uric acid can be intercalated inside the graphene layers, interconnecting the graphene layers and o-CNTs by forming hydrogen bonds with the carboxyl groups. The Fourier transform infrared (FTIR) spectra (Figure 2) show a comparison of the UA, the binary mixture of graphene oxide with oxidized carbon nanotube (GO/o-CNT), and the ternary composition of (GO/UA/o-CNT).…”

“…The attachment to the graphene oxide of the oxidized carbon nanotube took place through the formation of hydrogen bonding between the amino groups of uric acid (UA) and the carboxylic groups of GO and o-CNT. Uric acid, because of its good adhesive properties, can form hydrogen bonds with carboxyl groups with an adhesion force of 1.62 nN . During the sonication and stirring at 80 °C, because of its excellent surface attachment properties, the uric acid can be intercalated inside the graphene layers, interconnecting the graphene layers and o-CNTs by forming hydrogen bonds with the carboxyl groups.…”