SciCombinator

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Concept: Calcium carbonate

335

To determine whether increasing calcium intake from dietary sources affects bone mineral density (BMD) and, if so, whether the effects are similar to those of calcium supplements.

Concepts: Osteoporosis, Bone, Vitamin D, Apatite, Water, Magnesium, Calcium, Calcium carbonate

177

Biological materials are often based on simple constituents and grown by the principle of self-assembly under ambient conditions. In particular, biomineralization approaches exploit efficient pathways of inorganic material synthesis. There is still a large gap between the complexity of natural systems and the practical utilization of bioinspired formation mechanisms. Here we describe a simple self-assembly route leading to a CaCO(3) microlens array, somewhat reminiscent of the brittlestars' microlenses, with uniform size and focal length, by using a minimum number of components and equipment at ambient conditions. The formation mechanism of the amorphous CaCO(3) microlens arrays was elucidated by confocal Raman spectroscopic imaging to be a two-step growth process mediated by the organic surfactant. CaCO(3) microlens arrays are easy to fabricate, biocompatible and functional in amorphous or more stable crystalline forms. This shows that advanced optical materials can be generated by a simple mineral precipitation.

Concepts: Optics, Mineral, Solid, Calcium carbonate, Metaphysics, Lens, Glass, Microlens

176

Carbonated hydroxyapatite is the mineral found in vertebrate bones and teeth, whereas invertebrates utilize calcium carbonate in their mineralized organs. In particular, stable amorphous calcium carbonate is found in many crustaceans. Here we report on an unusual, crystalline enamel-like apatite layer found in the mandibles of the arthropod Cherax quadricarinatus (freshwater crayfish). Despite their very different thermodynamic stabilities, amorphous calcium carbonate, amorphous calcium phosphate, calcite and fluorapatite coexist in well-defined functional layers in close proximity within the mandible. The softer amorphous minerals are found primarily in the bulk of the mandible whereas apatite, the harder and less soluble mineral, forms a wear-resistant, enamel-like coating of the molar tooth. Our findings suggest a unique case of convergent evolution, where similar functional challenges of mastication led to independent developments of structurally and mechanically similar, apatite-based layers in the teeth of genetically remote phyla: vertebrates and crustaceans.

Concepts: Arthropod, Calcium, Crustacean, Mineral, Calcium carbonate, Teeth, Crayfish, Aragonite

171

Highly dispersive strontium carbonate (SrCO3) nanostructures with uniform dumbbell, ellipsoid, and rod-like morphologies were synthesized in methanol solution without any additives. These SrCO3 were characterized by X-ray diffraction, field emission scanning electron microscopy, and N2 adsorption-desorption. The results showed that the reaction temperature and the methanol/water ratio had important effects on the morphologies of SrCO3 particles. The dumbbell-like SrCO3 exhibited a Broader-Emmett-Teller surface area of 14.9 m2 g-1 and an average pore size of about 32 nm with narrow pore size distribution. The formation mechanism of the SrCO3 crystal was preliminary presented.

Concepts: Electron, Electron microscope, Strontium, X-ray, Chemical reaction, Calcium carbonate, Scanning electron microscope, Strontianite

165

Chronic renal failure (CRF) is associated with the development of secondary hyperparathyroidism and vascular calcifications. We evaluated the efficacy of PA21, a new iron-based non-calcium phosphate binder, in controlling phosphocalcic disorders and preventing vascular calcifications in uremic rats. Rats with adenine-diet-induced CRF were randomized to receive either PA21 0.5%, 1.5% or 5% or calcium carbonate (CaCO3) 3% in the diet, for 4 weeks and were compared with uremic and non-uremic control groups. After 4 weeks' phosphate binder treatment, serum calcium, creatinine and body weight were similar between all CRF groups. Serum phosphorus was reduced with CaCO3 3% (2.06 mmol/l, P≤0.001), PA21 1.5% (2.29 mmol/l, P<0.05) and PA21 5% (2.21 mmol/l, P≤0.001) versus CRF controls (2.91 mmol/l). Intact parathyroid hormone was strongly reduced in the PA21 5% and CaCO3 3% CRF groups to a similar extent (1138 and 1299 pg/ml, respectively) versus CRF controls (3261 pg/ml, both P≤0.001). A lower serum fibroblast growth factor 23 concentration was observed in the PA21 5%, compared with CaCO3 3% and CRF, control groups. PA21 5% CRF rats had a lower vascular calcification score compared with CaCO3 3% CRF rats and CRF controls. In conclusion, PA21 was as effective as CaCO3 at controlling phosphocalcic disorders but superior in preventing the development of vascular calcifications in uremic rats. Thus, PA21 represents a possible alternative to calcium-based phosphate binders in CRF patients.

Concepts: Renal failure, Nephrology, Carbon dioxide, Parathyroid hormone, Calcium carbonate, Hyperparathyroidism, Organ failure, Phosphate binders

155

Fish otoliths, biominerals composed of calcium carbonate with a small amount of organic matrix, are involved in the functioning of the inner ear. Starmaker (Stm) from zebrafish (Danio rerio) was the first protein found to be capable of controlling the formation of otoliths. Recently, a gene was identified encoding the Starmaker-like (Stm-l) protein from medaka (Oryzias latipes), a putative homologue of Stm and human dentine sialophosphoprotein. Although there is no sequence similarity between Stm-l and Stm, Stm-l was suggested to be involved in the biomineralization of otoliths, as had been observed for Stm even before. The molecular properties and functioning of Stm-l as a putative regulatory protein in otolith formation have not been characterized yet. A comprehensive biochemical and biophysical analysis of recombinant Stm-l, along with in silico examinations, indicated that Stm-l exhibits properties of a coil-like intrinsically disordered protein. Stm-l possesses an elongated and pliable structure that is able to adopt a more ordered and rigid conformation under the influence of different factors. An in vitro assay of the biomineralization activity of Stm-l indicated that Stm-l affected the size, shape and number of calcium carbonate crystals. The functional significance of intrinsically disordered properties of Stm-l and the possible role of this protein in controlling the formation of calcium carbonate crystals is discussed.

Concepts: DNA, Molecular biology, Model organism, Biochemistry, Calcium carbonate, Inner ear, Oryzias latipes, Oryzias

147

A chemiluminescence (CL) amplification platform based on HCC/Lucigenin&GOx (HLG) film was developed. Hollow structural calcium carbonate (HCC) particles were used as alternative materials for carrying both enzyme and CL reagent. The model enzyme (GOx), immobilized in confined space of HCC particles, exhibited an improved biocatalysis. The Michaelis constant (Km) and the enzymatic rate constant (kcat) were determined to be 0.209 μM and 2.21 s(-1), respectively, which are much better than those of either free GOx in aqueous solution or the GOx immobilized on common nanomaterials. Based on the HLG platform, CL signal was effectively amplified and visualized after adding trace glucose, which could be attributed to the HCC particles' high biocompatibility, large specific surface area, attractive interfacial properties and efficient interaction with analyses. The visual CL bioplatform showed an excellent performance with high selectivity, wide linear range and low detection limit for sensing trace glucose. Because it eliminates the need of complicated assembly procedure and enables visualization by the naked eye, the sensitive and selective CL bioplatform would provide wide potential applications in disease diagnosis and food safety.

Concepts: Signal transduction, Enzyme, Glucose, Catalysis, Calcium carbonate, Chemical kinetics, Glucose meter, Specific surface area

144

Ferric citrate (FC) has demonstrated efficacy as a phosphate binder and reduces the requirements for erythropoiesis-stimulating agents (ESAs) and intravenous (IV) iron in dialysis patients. We developed a net budgetary impact model to evaluate FC vs. other phosphate binders from the vantage of a large dialysis provider. We used a Markov microsimulation model to simulate mutually referential longitudinal effects between serum phosphate and phosphate binder dose; categories of these defined health states. Health states probabilistically determined treatment attendance and utilization of ESA and IV iron. We derived model inputs from a retrospective analysis of incident phosphate binder users from a large dialysis organization (January 2011-June 2013) and incorporated treatment effects of FC from a phase III trial. The model was run over a 1-year time horizon. We considered fixed costs of providing dialysis; costs of administering ESA and IV iron; and payment rates for dialysis, ESAs, and IV iron. In the base-case model, FC had a net budgetary impact (savings) of +US$213,223/year per 100 patients treated vs. standard of care. One-way sensitivity analyses showed a net budgetary impact of up to +US$316,296/year per 100 patients treated when higher hemoglobin levels observed with FC translated into a 30% additional ESA dose reduction, and up to +US$223,281/year per 100 patients treated when effects on missed treatment rates were varied. Two-way sensitivity analyses in which acquisition costs for ESA and IV iron were varied showed a net budgetary impact of +US$104,840 to +US$213,223/year per 100 patients treated. FC as a first-line phosphate binder would likely yield substantive savings vs. standard of care under current reimbursement.

Concepts: Nephrology, Iron, Retrospective, Calcium carbonate, Das Model, Renal osteodystrophy, Phosphate binders, Hyperphosphatemia

67

Anthropogenic emissions of carbon dioxide (CO2) are causing ocean acidification, lowering seawater aragonite (CaCO3) saturation state (Ωarag), with potentially substantial impacts on marine ecosystems over the 21(st) Century. Calcifying organisms have exhibited reduced calcification under lower saturation state conditions in aquaria. However, the in situ sensitivity of calcifying ecosystems to future ocean acidification remains unknown. Here we assess the community level sensitivity of calcification to local CO2-induced acidification caused by natural respiration in an unperturbed, biodiverse, temperate intertidal ecosystem. We find that on hourly timescales nighttime community calcification is strongly influenced by Ωarag, with greater net calcium carbonate dissolution under more acidic conditions. Daytime calcification however, is not detectably affected by Ωarag. If the short-term sensitivity of community calcification to Ωarag is representative of the long-term sensitivity to ocean acidification, nighttime dissolution in these intertidal ecosystems could more than double by 2050, with significant ecological and economic consequences.

Concepts: Oxygen, Carbon dioxide, Calcium, Ecosystem, Carbon, Calcium carbonate, Calcite, Aragonite

35

Coralline algae are a significant component of the benthic ecosystem. Their ability to withstand physical stresses in high energy environments relies on their skeletal structure which is composed of high Mg-calcite. High Mg-calcite is, however, the most soluble form of calcium carbonate and therefore potentially vulnerable to the change in carbonate chemistry resulting from the absorption of anthropogenic CO2 by the ocean. We examine the geochemistry of the cold water coralline alga Lithothamnion glaciale grown under predicted future (year 2050) high pCO2 (589 μatm) using Electron microprobe and NanoSIMS analysis. In the natural and control material, higher Mg calcite forms clear concentric bands around the algal cells. As expected, summer growth has a higher Mg content compared to the winter growth. In contrast, under elevated CO2 no banding of Mg is recognisable and overall Mg concentrations are lower. This reduction in Mg in the carbonate undermines the accuracy of the Mg/Ca ratio as proxy for past temperatures in time intervals with significantly different carbonate chemistry. Fundamentally, the loss of Mg in the calcite may reduce elasticity thereby changing the structural properties, which may affect the ability of L. glaciale to efficiently function as a habitat former in the future ocean.

Concepts: Algae, Cyanobacteria, Photosynthesis, Carbon dioxide, Coral reef, Calcium carbonate, Red algae, Coralline algae