Calcium polymorphs

A significant advantage of the PLM is in the differentiation and recognition of various forms of the same chemical substance polymorphic forms, eg, brookite, mtile, and anatase, three forms of titanium dioxide calcite, aragonite and vaterite, all forms of calcium carbonate Eorms I, II, III, and IV of HMX (a high explosive), etc. This is an important appHcation because most elements and compounds possess different crystal forms with very different physical properties. PLM is the only instmment mandated by the U.S. Environmental Protection Agency (EPA) for the detection and identification of the six forms of asbestos (qv) and other fibers in bulk samples. 

Calcium Pyrophosphates. As is typical of the pyrophosphate salts of multiple-charged or heavy-metal ions, the calcium pyrophosphates are extremely insoluble ia water. Calcium pyrophosphate exists ia three polymorphic modifications, each of which is metastable at room temperature. These are formed progressively upon thermal dehydration of calcium hydrogen phosphate dihydrate as shown below. Conversion temperatures indicated are those obtained from thermal analyses (22,23). The presence of impurities and actual processing conditions can change these values considerably, as is tme of commercial manufacture. 

Of course, freezing of a liquid - or its inverse - are themselves phase transformations, but the scientific study of freezing and melting was not developed until well into the 20th century (Section 9.1.1). Polymorphism also links with metastability thus aragonite, one polymorphic form of calcium carbonate, is under most circumstances metastable to the more familiar form, calcite. 

Thermotropic liquid-crystalline properties of different metal alkanesulfonates are studied by microscopy and X-ray diffraction [59]. Sodium soaps show smectic polymorphism of smectic A and smectic B phases. Ammonium soaps only show smectic A phases but polymorphism in the crystalline state. Calcium soaps show columnar mesophases. In Figs. 32 and 33 some textures and x-ray diffraction patterns are depicted. 

Spherical vaterite crystals were obtained with 4-mercaptobenzoic acid protected gold nanoparticles as the nucleation template by the carbonate diffusion method [51]. The crystallization of calcium carbonate in the absence of the 4-MBA capped gold nanoparticles resulted in calcite crystals. This indicates that the polymorphs of CaCOj were controlled by the acid-terminated gold nanoparticles. This result indicates that the rigid carboxylic acid structures can play a role in initiating the nucleation of vaterite as in the case of the G4.5 PAMAM dendrimer described above. 

Table 7 shows the calculated weight percent of calcium carbonate and titanium dioxide in the white-colored paint sample. These levels are based on the calcium and titanium levels shown in Table 6. Calcium carbonate was evident by the FTIR spectrum acquired from the dried paint sample, shown in Figure 13. (Flad it been available, Raman spectroscopy, which gives ready access to the low wavenumber region, could have been used to confirm the presence (and polymorphic form) of titanium dioxide [4].) Given the white color of the paint, it is likely that the titanium present was present as titanium dioxide, and this was assumed in the calculations. The calculated weight percentage of calcium carbonate in the dried paint is 21.7 wt%, and 12.6 wt% in the paint containing the solvents. The titanium dioxide levels were calculated to be 30.6 and 17.7 wt% in the dried and solvent-containing paint sample, respectively.

Fig. 6.2 Thermodynamic stability of calcium carbonates. Change in enthalpy is shown with polymorph.

Wada, N., Yamashita, K. and Umegaki, T. (1995) Effects of divalent cations upon nucleation, growth and transformation of calcium carbonate polymorphs under conditions of double diffusion. Journal of Crystal Growth, 148, 297-304. 

The packing arrangement of atoms or molecules in a crystalline solid phase is generally not unique, and for organic molecules in particular, it is common for two or more crystalline forms of the same substance to exist. The most familiar example in elemental terms is Graphite and Diamond. Both are composed entirely of the element Carbon, however their ciystal structures are very different, and so too are their physical properties. Calcium Carbonate is another common example with three polymorphic forms Calcite, Aragonite and Vaterite. 

A single substance may crystallise in more than one of seven crystal systems, all of which differ in their lattice arrangement, and exhibit not only different basic shapes but also different physical properties. A substance capable of forming more than one different crystal is said to exhibit polymorphism, and the different forms are called polymorphs. Calcium carbonate, for example, has three polymorphs — calcite (hexagonal),... 

Sverjensky DA, Shock EL, Helgeson HC (1997) Prediction of flie thermodynamic properties of aqueous metal complexes to 1000°C and 5 kb. Geochim Cosmochim Acta 61 1359-1412 Tarutani T, Clayton RN, Mayeda TK (1969) The effect of polymorphism and magnesium substitution on oxygen isotope fractionation between calcium carbonate and water. Geochim Cosmochim Acta 33 987-996... 

Fig. 7.1 Localization of some mutations and polymorphisms reported for the calcium-sensing receptor (CASK). The relationship between the CASK gene exons (II to Vll) and the modular domains of the 1078-amino acid protein are indicated. The 610-amino acid exctracellular domain (BCD) is encoded by exons II to VI. The beginning of exon VII encodes the BCD. The remainder of exon VII encodes the transmembrane domain (TMD) of approx. 250 amino acids that includes the membrane-spanning helices TM1-TM7 (indicated by the hatched boxes), the extracellular and intracellular...

There are many polymorphisms scattered across the more than 100 kb of genomic DNA that encodes the CASR protein however, the common missense SNPs (Ala986Ser, Arg990Gly, and GlnlOllGlu) are all clustered in the 3 cytoplasmic tail (13,14). The most common of these, the Ala986Ser variant, has proven to be predictive of the unbound, extracellular calcium fraction ("/5,76). Other CASR SNPs may also be important (17) in the general population. 

The S-HT variants such as H452Y have been associated with decreased calcium flux in response to clozapine that likely results from decreased Gq signaling (97,102-106). It is interesting to note that while depression has not been consistently associated with S-HT polymorphisms, such as -1348A/G in the promoter, no response to the antidepressant citralopram may be associated with in these... 

Heath, H., Odelberg, S., Jackson, C. E., et al. (1996) Clustered inactivating mutations and benign polymorphisms of the calcium receptor gene in familial benign hypocalciuric hypercalcemia suggest receptor functional domains. J. Clin. Endocrinol. Metab. 81, 1312-1317. 

Scillitani, A., Guarnieri, V., De Geronimo, S., et al. (2004) Blood ionized calcium is associated with clustered polymorphisms in the carboxyl-terminal tail of the calcium-sensing receptor. J. Clin. Endocrinol. Metab. 89, 5634—5638. 

Lorentzon, M., Lorentzon, R., Lerner, U. H., and Nordstrom, P. (2001) Calcium sensing receptor gene polymorphism, circulating calcium concentrations and bone mineral density in healthy adolescent girls. Eur. J. Endocrinol. 144, 257-261. 

Concerning calcium carbonate polymorphs calcite and aragonite, the experiments of Romanek et al. (1992) at low T (10 to 40 °C) seem to indicate that the enrichment factor of in the solid phase for CaC03-C02 partitioning is reduced by about two units in the aragonite polymorph with respect to the calcite counterpart, r being equal (e.g., at T = 10 °C, 1000 In a 13 for calcite-C02 and 11 for... 

Abrams, S. A., Griffin, I. J., Hawthorne, K. M., Chen, Z., Gunn, S. K., Wilde, M., Darlington, G., Shypailo, R. J., and Ellis, K. J. (2005a). Vitamin D receptor Fokl polymorphisms affect calcium absorption, kinetics, and bone mineralization rates during puberty. JBMR 20, 945-953. 

Ames, S., Ellis, K., Gurm, S., Copeland, K., and Abrams, S. (1999). Vitamin D receptor gene Fokl polymorphism predicts calcium absorption and bone mineral density in children. JBMR 14, 740-746. 

CYP3A4 Midazolam, triazolam, cyclosporine, erythromycin, HIV protease inhibitors, calcium channel blockers Polymorphic... 

---