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Phase Transitions of Calcium Oxalate Trihydrate and Epitaxy in the Weddellite-Whewellite System

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Phase Transitions of Calcium Oxalate Trihydrate and Epitaxy in the Weddellite-Whewellite System Scanning Electron Microscopy Volume 1986 Number 4 Article 45 8-30-1986 Phase Transitions of Calcium Oxalate Trihydrate and Epitaxy in the Weddellite-Whewellite System Sergio Deganello University of Chicago Follow this and additional works at: https://digitalcommons.usu.edu/electron Part of the Life Sciences Commons Recommended Citation Deganello, Sergio (1986) "Phase Transitions of Calcium Oxalate Trihydrate and Epitaxy in the Weddellite- Whewellite System," Scanning Electron Microscopy: Vol. 1986 : No. 4 , Article 45. Available at: https://digitalcommons.usu.edu/electron/vol1986/iss4/45 This Article is brought to you for free and open access by the Western Dairy Center at DigitalCommons@USU. It has been accepted for inclusion in Scanning Electron Microscopy by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. SCANNING ELECTRON MICROSCOPY /1986/IV (Pages 1721-1728) 0586-5581/86$1.00+0S SEM Inc., AMF O'Hare (Chicago), IL 60666-0507 USA PHASE TRANSITIONS OF CALCIUM OXALATE TRIHYDRATE AND EPITAXY IN THE WEDDELLITE-WHEWELLITESYSTEM Sergio Deganello * Nephrology Program, University of Chicago, IL and Institute of Mineralogy, University of Palermo, Italy (Received for publication April 07, 1986, and in revised form August 30, 1986) Abstract Introduction The phase changes calcium oxalate Only rarely is calcium oxalate trihydrate-weddellite, weddellite-calcium trihydrate (COT) found in urine or in oxalate monohydrate and calcium oxalate renal calculi. Nevertheless COT has trihydrate-whewellite are individually received much attention (i.e., Gardner, examined at the atomic level from a 1975) due to the possibility that it may theoretical point of view; concomitantly be a precursor to the formation of the topological requirements necessary for whewellite (COM) and weddellite (COD) in phase stability are clarified for each human kidney stones. Such uncertainty structure type. In solution a sequential stems from the failure to detect COT in series of phase transitions according to voided human urine containing calcium the steps calcium oxalate trihydrate­ oxalate crystalluria as well as from the weddellite-whewellite is not likely to be results of studies carried out in vitro. energetically favoured; direct conversion These indicate that calcium oxalate of calcium oxalate trihydrate to crystallizes as COD and/or COM from whewellite should be, instead, ordinarily solutions whose composition approaches expected. that expected to be found at physiological It is formally demonstrated that along conditions. two axial directions a set of atoms is in The hypothesis that the structural essentially identical positions in both control of one phase facilitates the weddellite and whewellite. This formation of another one is not novel in notwithstanding, it is concluded that urolithiasis. Actually it has long been epitactic catalysis cannot and should not upheld (i.e., Lonsdale, 1968) that be considered a common mechanism for the epitactic catalysis is of critical formation of whewellite from weddellite importance to the production of the (and vice versa) or of kidney stones in various kidney stone-forming salts. This general. notwithstanding, the actual relevance of epitaxy in kidney-stone formation has never been demonstrated. Furthermore recent evidence discounts its importance in a number of kidney-stone associations specifically tested for evidence of epitaxial overgrowths (e,g,,Leusmann et al,,1984; Deganello and Chou,1984), Therefore it is the purpose of this Key words: Calcium oxalate trihydrate, work to analyze at the atomic level the weddellite, whewellite, crystal requirements necessary for COT to invert, structures, calcium oxalate trihydrate­ respectively, to COD and COM. Furthermore weddellite phase change, weddellite­ the atomic constraints controlling the whewellite phase change, calcium oxalate process of epitaxy in the association COM­ trihydrate-whewellite phase change, COD will be first analyzed and then epitaxy, clinical relevance. discussed in light of their clinical significance, In an accompanying paper such approaches will be amplified to discuss the factors controlling the stability of * Address for correspondence: SCL,Box 42, COT and establish how and why selected The University of Chicago,5735 S.Ellis, inhibitors interact with its crystal Chicago, IL 60637 structure as well as those of COD and COM. Phone no.: (312) 962-7062 1721 S. Deganello Results and Discussion Structure of COT, For a detailed description of the crystal structure of COT the reader is referred to the specialized literature (Deganello et al.,1981). Here I report only enough data to clarify the ensuing discussion. Figure 1 shows that the bulk of the structure consists of dimers of calcium-centered polyhedra arranged according to triclinic symmetry (PI). These dimers are made up by two monomers, each consisting of a polyhedron defined by one calcium atom and eight oxygen ligands. Of these eight oxygen ligands, three belong to water molecules. The remaining five ligands instead, partake in forming two oxalate groups, Adjacent dimers bridge with one another to form sheets by bonding with oxalate groups (marked with OX,l in Fig. Fig, 1, Projection of the crystal 1) and oxygen and hydrogen atoms from the structure of COT down (001). Arrows water molecules, All of this results in indicate direction of open channels. Heavy large channels which delimit the hydrogen dots represent water-oxygens (W's). Dashed bond-network. Such channels are absent in lines show organization of latter ones, Ca COD and COM. Vertical continuity is stands for calcium atom. O's indicate assured by the juxtaposition of the sheets oxygen ligands while H's are hydrogen onto one another through selective bonding atoms. with another set of oxalate groups. These are perpendicular to their OX.I counter­ parts. The phase change COT-COD, If enough activation energy is available to disrupt the W(3)-W( 1), 0(2) '-W( 1) and W(3) '-W(2) bond-configurations (Fig. 1), the oxygen ligands 0(2) and W(3) 1 can coalesce onto, respectively, their W(3) and 0(2)'counter­ parts (Fig. 2a). The resemblance of the ensuing atomic arrangement to that of COD (Fig. 2b) is patent even though no cor­ rections have been made for the straiten­ ing of the structure, Adjacent dimers now share common atomic edges [the W(3)-0(2)'s in Fig. 1) with the result that the channels produced by the hydrogen bond­ network are destroyed. Most of these changes can be readily appreciated even from the standpoint of the water molecules alone (Figs. 3,2a and 2b). It is not, in fact, topologically possible to proceed from COT to COD by condensation of atomic Fig. 2a. Reconstruction of initial stages of COT-COD phase-transition. Heavy dots represent water-oxygens (W). Open circles stand for oxygen ligands. Notice that only two water molecules are availa­ ble in each polyhedron, Fig. 2b, A section of crystal structure of COD viewed down (010). Heavy dots stand for water-oxygens. Open circles stand for oxygen ligands, Dotted lines indicate hydrogen-bond configuration. Notice that oxalate group OX,I'(in bold) is perpen­ dicular to its OX.I counterpart which lays on plane of figure. Arrows indicate direction along which the calcium-centered polyhedra shift into their counterparts. 1722 Phase Transitions and Epitaxy in Oxalates Fig. 4. A more complete view of the crystal structure of COM as seen down [001) (P2 /a setting). Dots represent 1 water-oxygens; open circles show oxygen ligands; dashed lines stress architecture of water molecules; Ca stands for calcium atom. Notice that the C(3)-C(4) oxalate group (in bold) is perpendicular to its Fig. 3. Transition to COM. Two calcium­ C(l)-C(2) counterpart which lays on plane centered polyhedra (Fig. 2b) have shifted of projection. into one another. Consequenthly both share oxygens from the same oxalate group. ligands bonds to a water molecule; the Heavy dots represent water-oxygens. Open remaining seven, instead, are shared with circles stand for oxygen ligands. five different oxalate groups. All of this results in planar sheets of calcium and units already present since a significant oxygen atoms which juxtapose onto one an­ rearrangement of the entire water-molecule other along the c axis. This juxtaposition is controlled by sets of C(3)-C(4)o configuration is necessary. In COD only 4 two of the eight oxygens of the calcium­ oxalate groups. These are perpendicular to their C(l)-C(2)0 counterparts laying on centered polyhedra belong to water 4 molecules; the remaining ones, instead, the plane of the sheets. Because of these partake in making four, rather than two, changes COM gains in stability with oxalate groups as is observed in COT. respect to COD, measures higher specific Because of the above and the elimination gravity (2.21 g/cm3), and tends to resist of the voids associated with the hydrogen further dehydration. Actually, even if one bond-network, the structure of COD is more manages to dehydrate COM to anhydrous compact (specific gravity: 1.996 vs 1.887 calcium oxalate (alpha), this still g/cm 3 for COT) and more resistant to retains an exceptional propensity to phononic and chemical destabilization. reacquire its pretransition configuration. COD crystallizes in a tetragonal space Fig. 5 shows a Guinier-Lenne' photograph group (I4/m). It is likely that the of anhydrous calcium oxalate taken under process of phase transition COT-COD vacuum and at 70°C. As soon as either the affects first the W(2)-0(3) (3.031 A) and vacuum or the temperature, or both are then the W(3)-W(l) (2.983 A) bonds because released, the structure instantaneously of their longer length and thus, lower reverts to that of COM. Single-crystal bond strength (Pauling, 1960). The phase photographs (precession camera) taken of change COT-COD is discontinuous or, anhydrous calcium oxalate using a heating according to the nomenclature of Buerger device locally developed (Deganello,1982) (1961), a reconstructive one.
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