Barium ions, blocking

Components in the invading water-based filtrate and in the formation waters may react to form insoluble precipitates which can block the pores and give rise to skin damage. The scale can be formed by interaction of calcium-based brines with carbon dioxide or sulfate ions in the formation water. Alternatively sulfate ions in the invading fluid may react with calcium or barium ions in the formation water. Analysis of the formation water can identify whether such a problem may arise. 

Barium sulfate is a radiopaque or contrast agent that blocks the transmission X-rays to help physicians see any special conditions that may exist in an organ or that part of the body where the contrast agent is localized. The areas in which radiopaque agents are located will appear white on X-ray film, creating the needed distinction, or contrast, between one organ and other tissues. How can the toxicity of the barium ion be controlled to provide this necessary radiopaque function ... 

Some metals, such as cadmium, cobalt, and lead, are selectively car-diotoxic. They depress contractivity and slow down conduction in the cardiac-system. They may also cause morphological alterations, e.g., cobalt, which was once used to prevent excessive foam formation in beers, caused cardiomyopathy among heavy beer drinkers. Some of the metals also block ion channels in myocytes. Manganese and nickel block calcium channels, whereas barium is a strong inducer of cardiac arrhythmia. 

Another pattern can be found in the charges of the ions (Fig. C.5). For elements in Groups 1 and 2, for instance, the charge of the ions is equal to the group number. Thus, cesium in Group l forms Cs+ ions barium in Group 2 forms Ba2+ ions. Why this is so will become clear in Chapter 1. Figure C.5 also shows that atoms of the d-block elements and... 

An s-block element has a low ionization energy, which means its outermost electrons can be lost easily. A Group 1 element is likely to form +1 ions, such as Li+, Na+, and K+. Group 2 elements similarly form +2 ions, such as Mg2+, Ca2+, and Ba2+. An s-block element is likely to be a reactive metal with all the features that the name metal implies (Fig. 1.48, Table 1.4). Because ionization energies are lowest at the bottom of each group, and the elements there lose their valence electrons most easily, the heavy elements cesium and barium react most vigorously of all s-block elements. They have to be kept stored out of contact with air and water. The alkali metals have few direct uses as materials but are enormously important as compounds. 

For conductance work, ions other than those resulting from the ionization of water itself must be reduced to the lowest possible concentrations. If distilled water is used, it should be triply distilled (ordinary distilled water distilled a second time from dilute acidified permanganate to oxidize organic impurities and a third time with a block-tin condenser from dilute barium hydroxide to remove volatile acids and CO2). Conductivity water should be stored in polyethylene bottles in order to prevent leaching of soluble constituents from the surface of a glass botde. Exposure to air should be minimized to prevent contamination with carbon dioxide. 

The central water cavity (basically designed to stabilize cations in the cavity) helps stabilize ions at the cavity-filter boundary, which may account for the location of the barium block site. 

The main experimental use of barium is in electrophysiology where it can be used as a charged probe for metal ion-dependent processes. The isolation and identification of individual ion fluxes which contribute to the electric currents flowing through cell membranes often requires techniques to block specific components of electrical activity. This can sometimes be achieved by the use of the soluble salts of divalent cations such as barium and manganese which may block potassium and calcium and currents in, for example, the cardiac pacemaker [4]. Barium can also be used to identify potassium-conducting channels in isolated membrane vesicles [S,6] or calcium charmels in isolated heart muscle cells, myocytes [7], and adrenal gland chromaffin cells [8]. 

Soluble salts of barium block exit channel for ions, leading to hypokalemia stimulate both cardiac and smooth muscle... 

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