Supporting Information

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1 Elucidating the Effects of Polyprotic Acid Speciation in Calcium Oxalate Crystallization Jihae Chung, Ricardo Sosa, and Jeffrey D. Rimer * University of Houston, Department of Chemical and Biomolecular Engineering, Houston, TX *Correspondence sent to jrimer@central.uh.edu Supporting Information Table of Contents Page S1. Speciation Model Calculations S2 S2. Effect of ph on COM Crystal Habit S5 S3. Supporting References S6 List of Figures and Tables Figure S1. Figure S2. Figure S3. Figure S4. Table S1. Speciation model results for CA and HCA as a function of distance from COM surfaces (at ph 4 8) Changes in the relative growth rate as a function of CaOx supersaturation Length and width of COM crystals prepared in the absence and in the presence of CA and HCA at ph 4 10 Population of COM crystals obtained in the absence and in the presence of CA and HCA at ph 4 10 Hydrated radius of ions at 25ºC from literature S1

2 S1. Speciation Model Calculations Species fractions of oxalate, citrate, and hydroxycitrate presented in Figure 2 were calculated using the equations in Table 1. To highlight model calculations, we select citrate with its three dissociation constants:, (S1), and (S2). (S3) All experiments were performed in aqueous solution, thus we account for water dissociation,. (S4) The ionic strength was set to 150 mm using NaCl. The net charge of electrolytes in solution is neutral, 0 2 3, (S5) or if we simplify the equation by substituting the citrate and water dissociation constants, 0 2 Total amount of citrate in solution equals to the sum of all the species in solution, 3. (S6) (S7) where is the amount of citrate added in the experimental study. We can further simplify Equation S7 by substituting the citrate dissociation constants,. (S8) All concentrations were replaced with activity, a = C. The activity coefficients were calculated with the Davies equation, log , (S9) where z is the ion charge and is the ionic strength. The combination of Equations S1 to S9 yields two equations with two unknowns: and. For each ph (or value) we can calculate the fraction of each citrate species. A similar approach was used for other acids (OX and HCA). We also approximated the fraction of neutral and charged species as a function of distance from a COM crystal surface using a combination of the above equations and the colloidal relationships for charged interfaces (see Equations in the manuscript). Species profiles of CA and HCA are shown in Figure S1 at bulk ph values 4 8 (the profiles for OX are reported in Figure 2d f). At ph 5, the percentage of fully dissociated citrate, CA(-3), at COM crystal surfaces is less than 1 %, but it becomes the dominant species at ph 7 in which ca. 64% of CA is fully dissociated at the surface as opposed to ca. 80% in bulk solution. The difference between surface and bulk CA concentration narrows at ph 8. In the case of HCA, 20% is HCA(-3) at the crystal surface and ca. 40% in the bulk at ph 5. Concentrations of HCA(-3) at the surface and in bulk solution are similar at ph 6. S2

3 Figure S1. Fractions of citrate (CA) species (a) and hydroxycitrate (HCA) species (b) in their neutral, monovalent, divalent, and trivalent states. Calculations at ph 4 8 were made as a function of distance from a COM crystal surface. S3

4 Table S1. Hydrated radius of ions at 25ºC (used to calculate activity coefficients in the speciation model). Species α (pm) Ca C 2 O Na Cl Hydrated radii are obtained from ref.s1 1. Figure S2. Rate of calcium depletion at room temperature during COM crystallization in the absence of modifier. Data points are the average of at least five separate ISE measurements at varying CaOx concentration. The solid line is linear regression and the error bars equal two standard deviations. S4

5 S2. Effect of ph on COM Crystal Habit Figure S3. Influence of ph on bulk COM crystal habit: (a) changes in the length of crystals measured along the [001] direction, and (b) changes in the width of crystals measured along the [010] direction. Data were extracted from optical microscopy images of three separate batches of crystals prepared in the absence of modifier (control, gray) and in the presence of citrate (orange) and hydroxycitrate (blue). The concentration of modifier was fixed at 20 g/ml. Error bars equal one standard deviation. In Figure S3 we compare the distributions of COM crystal length and width (refer to Figure 1a). Crystals were prepared at ph 4 10 in the absence and presence of modifiers (20 g/ml). The relatively large standard deviation of data reflects the polydispersity of crystal size. At ph 4, the presence of modifiers leads to a marginal increase in crystal dimensions (c and b), though the aspect ratio (c/b) is unaffected (refer to Figure 6a). As the solution alkalinity is increased (ph > 6), the length of COM crystals is increased in the absence and in the presence of CA; however, HCA has little effect on the length of COM crystals, most likely because HCA is fully dissociated at ph > 6. For a similar reason, the presence of fully dissociated CA at ph > 8 leads to a more dramatic increase in the length of COM crystals. The width of COM crystals is relatively constant in the absence of modifiers, which results in a net increase in the c/b aspect ratio. HCA increases the width of COM crystals owing to its preference for binding to {12-1} and {021} surfaces, rendering growth in the [010] direction more dominant than in the [001] direction. S5

6 Figure S4. The number of COM crystals collected prior to bulk crystallization was measured absence (i.e., control, gray) and in the presence of C CA = 20 g/ml (orange) and C HCA = 20 g/ml (blue), respectively, at ph values Data were obtained from three separate batches and the error bars indicate one standard deviation. In Figure S4 we compare the number of COM crystals (N COM ) formed in the absence and presence of modifiers (20 g/ml). N COM was measured by counting the crystals collected on the glass substrate used in bulk crystallization assays. Sixteen optical micrographs (each micrograph area equals 647 m 484 m) were obtained from different regions of the substrate and three separate batches were analyzed. At ph 4, N COM is significantly reduced due to the lack of fully dissociated oxalate, OX(-2), in the growth solution. This leads to a dramatic reduction in COM nucleation. Interestingly, the presence of CA and HCA increase N COM, which is consistent with our kinetic study revealing modifiers to be growth promoters at low ph (refer to Figure 4). At ph 5, approximately 80% of OX is fully dissociated in bulk solution and there is a marked increase in N COM. At ph 5, modifiers reduce N COM relative to the control, with the exception of ph 10 where N COM is again higher for modifiers than for the control. The overall trend for N COM is consistent in the absence and presence of modifiers, i.e., N COM increases with increasing ph as the fully-dissociated species of solute and modifier become more prominent. Once the fully dissociated states are reached, N COM decreases with further increase in solution ph. For instance, CA-containing growth solutions exhibit an increase in N COM with increasing ph until reaching ph 7 where additional increases in alkalinity result in a notable reduction in N COM. A similar trend is observed for HCA where the switch to decreasing N COM occurs at ph 5. The effects of modifiers at ph 10 is not well understood. S3. Supporting References 1. Harris, D., Quantitative chemical analysis. 8th ed.; W.H. Freeman and Company: New York, S6