The multiple effects of amino acids on the early stages of calcium carbonate crystallization

Abstract

Abstract. Proteins have found their way into many of Nature's structures due to their structural stability, diversity in function and composition, and ability to be regulated as well as be regulators themselves. In this study, we investigate the constitutive amino acids that make up some of these proteins which are involved in CaCO 3 mineralization -either in nucleation, crystal growth, or inhibition processes. By assaying all 20 amino acids with vapor diffusion and in situ potentiometric titration, we have found specific amino acids having multiple effects on the early stages of CaCO 3 crystallization. These same amino acids have been independently implicated as constituents in liquid-like precursors that form mineralized tissues, processes believed to be key effects of biomineralization proteins in several biological model systems.

Modulating Nucleation by Kosmotropes and Chaotropes: Testing the Waters

“…During the course of the experiment, the pH is kept constant by the counter-titration of a base. Similar experiments have been previously performed to assess the effects of diverse additives including synthetic polymers [26], biomolecules such as amino acids [56], carbohydrates, polysaccharides [57,58], proteins [59], and peptides [60] as well as inorganic species such as silica and magnesium [61][62][63][64]. By employing ion-selective electrodes and precise reaction conditions, the diverse roles of additives on different aspects of mineral nucleation including the stability of PNCs, inhibition or promotion of nucleation, and the nature of the nucleated phase are demonstrated.…”

“…At pH 9.0, this corresponds to percentage increases of about 87,44,29,26, and 20%, respectively. At higher pH (9.75), these effects are more pronounced, leading to corresponding increases of about 41,56,66,109, and 39% in the pre-nucleation slope. In this regard, trehalose and mannitol suppress ionassociation and are effective pH-dependent destabilizers of PNCs.…”

“…Dataset analyses for the time developments of free Ca 2+ ion and pH are performed as described in previous literature [28,56,57]. For titrations performed in carbonate buffer, the detected free Ca 2+ ion concentration increases linearly with time at a rate significantly lower than that of Ca 2+ ion addition to water.…”

“…The effects of the small molecules on the time required for mineral nucleation are represented in Figure 2B. As introduced in previous studies [56,57], we apply a scaling factor (F) defined as the quotient of the average nucleation time in presence of an additive and that of the corresponding reference. At pH 9.75, several additives exhibit F values close to unity viz.…”

“…In the case of glycine, this is supported by the predominance of its base form above pH 9.5 ( Figure S1). The inhibitory effects introduced by these molecules are small, in comparison to those in the presence of polymeric additives such as poly(acrylic acid), poly(aspartic acid), carboxymethyl cellulose, and heparin [25,26,56,57]. Certain small molecules promote mineral nucleation at pH 9.0.…”