Complexed calcium

Calcium—Silicon. Calcium—silicon and calcium—barium—siUcon are made in the submerged-arc electric furnace by carbon reduction of lime, sihca rock, and barites. Commercial calcium—silicon contains 28—32% calcium, 60—65% siUcon, and 3% iron (max). Barium-bearing alloys contains 16—20% calcium, 9—12% barium, and 53—59% sihcon. Calcium can also be added as an ahoy containing 10—13% calcium, 14—18% barium, 19—21% aluminum, and 38—40% shicon These ahoys are used to deoxidize and degasify steel. They produce complex calcium shicate inclusions that are minimally harm fill to physical properties and prevent the formation of alumina-type inclusions, a principal source of fatigue failure in highly stressed ahoy steels. As a sulfide former, they promote random distribution of sulfides, thereby minimizing chain-type inclusions. In cast iron, they are used as an inoculant. 

S. Schuster, M. Marhl, and T. Hofer, Modelling of simple and complex calcium oscillations. From single-cell responses to intercellular signalling. Eur. J. Biochem. 269, 1333-1355 (2002). 

Glass-ionomers have been used in various areas of restorative dentistry since the mid 1970s. They were invented and originally described by Wilson and Kent [208], and consist of a basic glass powder and a water-soluble acidic polymer. The most widely used polymer is poly(acrylic acid), but acrylic/maleic acid copolymer is also widely used [209]. The glass powder is a complex calcium (or strontium) aluminofluorosilicate [210] that is typically at least partially phase separated. 

The main features of hypocalcemia are neuromuscular—tetany, paresthesias, laryngospasm, muscle cramps, and convulsions. The major causes of hypocalcemia in the adult are hypoparathyroidism, vitamin D deficiency, chronic kidney disease, and malabsorption. Neonatal hypocalcemia is a common disorder that usually resolves without therapy. The roles of PTH, vitamin D, and calcitonin in the neonatal syndrome are under active investigation. Large infusions of citrated blood can produce hypocalcemia by the formation of citrate-calcium complexes. Calcium and vitamin D (or its metabolites) form the mainstay of treatment of hypocalcemia. 

The major location of calcium in the body is in the skeleton, which contains more than 90% of the body calcium as phosphate and carbonate. Bone resorption and formation keeps this calcium in dynamic equilibrium with ionized and complexed calcium in blood, cellular fluids and membranes. Homeostasis is mainly regulated by the parathyroid hormone and vitamin D which lead to increased blood calcium levels, and by a thyroid hormone, calcitonin, which controls the plasma calcium concentration J5 Increasing the concentration of calcitonin decreases the blood calcium level, hence injections of calcitonin are used to treat severe hyperalcaemia arising from hyperparathyroidism, vitamin D intoxication or the injection of too high a level of parathyroid extract. High levels of calcitonin also decrease resorption of calcium from bone. Hypocalcaemia stimulates parathyroid activity, leading to increased release of calcium from bone, reduction in urinary excretion of calcium and increased absorption of calcium from the intestine. Urinary excretion of phosphate is enhanced. 

Heterocyclic mono(ring) complexes, calcium, strontium, barium metal halides, 2, 116... 

Vitamin B12 can be absorbed when present in physiological amounts only if it is first bound to a specific protein—the so-called intrinsic factor—that tightly binds to the vitamin. The complex then passes through the jejunum to the ileum, which contains receptor sites for the vitamin B12/intrinsic factor complex. Calcium ions are required for the reaction between ileal receptors and the intrinsic factor/vitamin B12 complex. The reaction is inhibited by EDTA and reduced by a pH below 5.4. The vitamin appears to be separated from intrinsic factor at the ileal receptor sites and is then bound to another protein carrier, transcobalamin II, which transports the vitamin and permits its uptake by a number of tissues. The subject has been well reviewed by Jacob and her colleagues (Jl). Removal of 60 cm of ileum may impair vitamin B12 absorption and with the loss of 180 cm absorption is almost always affected. 

Interest in detergent products derived from renewable resources and with better biodegradability has driven evaluation of oxidized sugars and starches as builders or co-builders in detergents.113 Builders and co-builders complex calcium and magnesium ions in hard water to prevent sealing or deposits due to precipitation of insoluble carbonate salts. In current powder detergents, the builders are usually zeolites used in combination with polycarboxylate polymers derived from synthetic acrylic-maleic acid copolymers.114... 

Vesuvian (Idocrase) Complex calcium aluminum silicate Opaque to translucent green or brown (a.k.a. Happy Camp jade ) 1.49-1.69 3 2.7... 

Oxalic acid is capable of combining with minerals to form salt complexes. Calcium and zinc form the least soluble salts with oxalic acid (, ). Spinach contains more oxalic acid than most foods (approximately 700 mg/100 g), and its effect on calcium availability has been studied rather extensively. Other green leafy vegetables also contain considerable amounts of oxalic acid, and the oxalic acid is concentrated more in the leaves than in the stalks (7 ). Rhubarb, some nuts, tea, and cocoa have also been found to contain oxalic acid in amounts greater than 200 mg/100 g food (7-jJJ. 

A recent potentiometric study supports the view of Siegfried and Howw-janz that, in solution at least, a complex calcium sucrose carbonate can exist. 

Chelating agent for complexing calcium and iron during high alkaline/temperature bleaching. Prevents silicate buildup on equipment. 

Hydrated Silicates of uranium occur in nature as gummite and allied minerals (see p. 273) uranophane or uranotil is a complex calcium uranyl silicate. 

At least part of the reason for these observations must be that precipitation is severely inhibited by organics such as humic acids (Berner et ai, 1978). Mitterer and co-authors (e.g., Mitterer and Cunningham, 1985) have explored the possible role of organic matter in cement formation. These authors suggested that, whereas some types of organic matter inhibit precipitation, other types, particularly those rich in aspartic acid, favor precipitation by complexing calcium. Inhibition of precipitation, coupled with slow transfer of fresh supersaturated seawater into sediment pores, seems to account for the lack of extensive early cementation. 

Oxo-anions can be considered as complexes. Calcium carbonate, for example, can be made from two stable, saturated compounds, CaO+COg- CaCOg, and its crystals contain COg " ions in which one carbon atom is attached to three oxygen atoms. Potassium perchlorate, KCIO4, and potassium fluoroborate, KBF, both have the same structure with discrete complex ions. The compounds K2SO4 and Cs2HgBr4 have not only the same rhombic form but the same crystallographic axial ratios in which a b c = = 1 0.74 0.57. 

In the presence of moisture, calcium salts may be incompatible with amines, amino acids, peptides, and proteins, which may form complexes. Calcium salts will interfere with the bioavailability of tetracycline antibiotics. It is also anticipated that calcium sulfate would be incompatible with indomethacin, aspirin, aspartame, ampicillin, cephalexin, and eryth-romycin " " since these materials are incompatible with other calcium salts. 

Complexed calcium, about 10%, is complexed with small diffusible morganic and organic anions, including bicarbonate, lactate, phosphate, and citrate. 

Free calcium Complexed calcium I— Free calcium —I... 

ISEs for the measurement of total calcium were introduced more recently than photometric methods. The specimen is acidified to convert protein-bound and complexed calcium to free calcium before measurement of calcium by ISE. Calcium ISEs are discussed later in this chapter. 

Three forms of calcium are in equilibrium in serum nondiffusible calcium bound primarily to albumin diffusible complexes of calcium with lactate, bicarbonate, phosphate, sulfate, citrate, and other anions and diffusible ionized calcium (Ca " ). Ionized calcium accounts for approximately half of total serum calcium, and nondiffusible and complexed calcium account for 45% and 5%, respectively. Ionized calcium is the physiological active form its concentration is regulated by the parathyroid gland. A decrease in serum ionized calcium can cause tetany (involuntary muscle contraction) and related neurological symptoms, regardless of the total serum calcium concentration. 

During the extraction, the colour of the CCI4-TBP phase changes from the orange-red of the Azo-azoxy BN to the red of the calcium Azo-azoxy BN complex. Calcium is stripped from the organic phase with water or dilute HCl. After this stripping, the CCI4 solution of Azo-azoxy BN may be reused. 

---