Calcium bridging

In the case of prothrombin and related clotting factors, interruption of the vitamin K cycle leads to the production of nonfunctional, undercarboxylated proteins, which are duly exported from hepatocytes into blood (Thijssen 1995). They are nonfunctional because there is a requirement for the additional carboxyl residues in the clotting process. Ionized carboxyl groups can establish links with negatively charged sites on neighboring phospholipid molecules of cell surfaces via calcium bridges. 

It is difficult to isolate only surface hpid or only internal lipid however, it is certain that both surface and internal hpid exist in hair. Koch suggests that the external lipid may be extracted by boiling ether saturated with water followed by ethereal hydrochloric acid. The former solvent removes neutral surface lipid the latter solvent removes calcium-bridged fatty acids attached to the hair surface. He suggests that surface lipid so defined is removed under conditions that simulate the strongest shampooing conditions imaginable. ... 

Calcium-bridged fatty acid may be deposited onto hair even in shampoos containing anionic surfactant such as ammonium lauryl sulfate. It is also well known that acid rinses may be used to remove calcium-bridged fatty acid from hair, and anionic sulfate surfactants appear to remove fatty acid deposits from hair. However, copper (cupric ion) adsorbs strongly to hair and is reported to be resistant to removal by anionic surfactant [11]. 

We are just as well informed regarding the structure of calcium silicide, which was described by Bohm and Hassel as a primary valence lattice of six-membered silicon rings linked together by calcium bridges. Fig. 46 shows diagrammatically the arrangement of atoms in this lattice as elucidated by thorough x-ray structure analysis. 

Studies have shown that high molecular weight anionic polyacrylamide polymers are most effective as soil stabUisers [76]. These polymers bind primarily to calcium ions that are in themselves bound to anionic sites on the surface of the soil crumb (a process known as calcium bridging or salt linkage). The anionic nature of the soil crumb arises due to the anionic surface charge of the clay portion within the sod. 

The time-dependent irreversible adhesion of the captured cell. Surface stabilization depends on calcium bridging, hydrophobic interactions and the formation of covalent bonds with surface groups at distances of less than 0-4 nm, or the establishment of polymer bridging at distances up to 10nm. 

Anions can also be bound by calcium bridges. The cation exchange is then equimolar [56] ... 

Anionic surfactants are adsorbed by smectites in acidic medium and, at pH near neutral, when inert salts (e.g., NaCl) are added to compress the diffuse ionic layers [53]. They can also be attached to the mineral surface by calcium bridges. 

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