Oxalate Monohydrate (oxalate + monohydrate)

Distribution by Scientific Domains

Kinds of Oxalate Monohydrate

  • calcium oxalate monohydrate


  • Selected Abstracts


    A study of primary nucleation of calcium oxalate monohydrate: II.

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2004
    Effect of urinary species
    Abstract Kidney stones consist of various organic and inorganic compounds. Calcium oxalate monohydrate (COM) is the main inorganic constituent of kidney stones. However, the mechanisms for the formation of calcium oxalate kidney stones are not well understood. In this regard, there are several hypotheses including nucleation, crystal growth and/or aggregation of formed COM crystals. The effect of some urinary species such as oxalate, calcium, citrate, and protein on nucleation and crystallization characteristics of COM is determined by measuring the weight of formed crystals and their size distributions under different chemical conditions, which simulate the urinary environment. Statistical experimental designs are used to determine the interaction effects among various factors. The data clearly show that oxalate and calcium promote nucleation and crystallization of COM. This is attributed to formation of a thermodynamically stable calcium oxalate monohydrate resulting from supersaturation. Citrate, however, inhibits nucleation and further crystal growth. These results are explained on the basis of the high affinity of citrate to combine with calcium to form soluble calcium citrate complexes. Thus, citrate competes with oxalate ion for binding to calcium cations. These conditions decrease the amount of free calcium ions available to form calcium oxalate crystals. In case of protein (mucin), however, the results suggest that no significant effect could be measured of mucin on nucleation and crystal growth. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Role of uric acid in different types of calcium oxalate renal calculi

    INTERNATIONAL JOURNAL OF UROLOGY, Issue 3 2006
    FÉLIX GRASES
    Aim:, The presence of uric acid in the beginning zone of different types of ,pure' calcium oxalate renal calculi was evaluated with the aim of establishing the degree of participation of uric acid crystals in the formation of such calculi. Methods:, The core or fragment of different types of ,pure' calcium oxalate renal calculi was detached, pulverized and uric acid extracted. Uric acid was determined using a high-performance liquid chromatography/mass spectrometry method. Results:, In calcium oxalate monohydrate (COM) papillary calculi with a core constituted by COM crystals and organic matter, 0.030 ± 0.007% uric acid was found in the core. In COM papillary calculi with a core constituted by hydroxyapatite, 0.031 ± 0.008% uric acid was found in the core. In COM unattached calculi (formed in renal cavities) with the core mainly formed by COM crystals and organic matter, 0.24 ± 0.09% uric acid was found in the core. In COM unattached calculi with the core formed by uric acid identifiable by scanning electron microscopy (SEM) coupled to X-ray microanalysis, 20.8 ± 7.8% uric acid was found in the core. In calcium oxalate dihydrate (COD) unattached calculi containing little amounts of organic matter, 0.012 ± 0.004% uric acid was found. In COD unattached calculi containing little amounts of organic matter and hydroxyapatite, 0.0030 ± 0.0004% of uric acid was found. Conclusions:, From these results it can be deduced that uric acid can play an important role as inducer (heterogeneous nucleant) of COM unattached calculi with the core formed by uric acid identifiable by SEM coupled to X-ray microanalysis (these calculi constitute the 1.2% of all calculi) and in COM unattached calculi with the core mainly formed by COM crystals and organic matter (these calculi constitute the 10.8% of all calculi). [source]


    Examination of whewellite kidney stones by scanning electron microscopy and powder neutron diffraction techniques

    JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2009
    Michel Daudon
    Kidney stones made of whewellite, i.e. calcium oxalate monohydrate, exhibit various morphological aspects. The crystalline structure of whewellite at the atomic scale was revisited through a single-crystal neutron study at room temperature using a four-circle automated diffractometer. The possible relationships between the various morphological types of whewellite stones and their structural characteristics were examined at the mesoscopic scale by the use of scanning electron microscopy and at the nanometric scale by powder neutron diffraction. All types of whewellite stones displayed a similar structure at the nanometric scale. However, significant differences were found at the mesoscopic scale. In particular, the crystallites in kidney stones resulting from a genetic hyperoxaluria exhibited a peculiar structure. There was a close relationship between stone morphology and crystallite organization at the mesoscopic level and the effectiveness of extracorporeal shockwave lithotripsy. [source]


    Growth and aggregation of vaterite in seeded-batch experiments

    AICHE JOURNAL, Issue 11 2004
    Jens-P.
    Abstract Seeded-batch crystallization experiments allowing study of the growth and aggregation of the Vaterite modification of calcium carbonate are reported. Results are reported for initial relative supersaturation (, = S , 1) values in the range 1.66 to 6.70, stirrer speeds in the range 400 and 1200 rpm, and at temperatures of 25 and 40°C. It is found that in all cases the linear rate of growth of the particles is size independent and depends on relative supersaturation squared. The aggregation process is apparently size independent with a rate constant that is directly proportional to the instantaneous growth rate and decreases with increasing stirrer speed. The behavior of the aggregation rate constant is very well described by the model recently proposed by Liew et al., in which the efficiency of the aggregation process is predicted to depend only on the dimensionless strength of the particles and the nature of the flow field. It is concluded that Vaterite forms aggregates with crystalline bridges having an effective strength of approximately 25% of that of calcite or calcium oxalate monohydrate. The fitted parameter L,*/M50 takes on a value of 0.18 ± 0.02. The kinetics and associated model are capable of describing the evolving particle size distributions very well. Finally, a hypothesis is advanced to describe the aggregation of small inorganic crystals in supersaturated solutions. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2772,2782, 2004 [source]


    A Micro-Mechanical Model for the Rate of Aggregation during Precipitation from Solution

    CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 3 2003
    T.L. Liew
    Abstract Our group has proposed [1,2] that the rate of aggregation between crystals in a supersaturated solution depends on the rate of collision and on the probability of that collision surviving. It has been suggested that the probability, or efficiency, depends on the strength of the newly formed neck between the crystals and the hydrodynamic force acting to pull them apart. That strength has been quantified by assuming that the crystals first touch at a point and thus the area of the neck increases with the square of time. In this paper, over 400 data points were considered for calcium oxalate monohydrate (COM), and more than 250 for calcite, relating the rate of aggregation in a stirred tank to the stirrer speed, the supersaturation and the particle size and show that the existing model cannot account for the relationship seen. It is proposed instead that the first contact between crystals lies along a line and thus the area of the neck grows linearly with time. A dimensionless strength formulated in this way is able to account for the dependence seen. [source]