Essential and Nonessential Elements

Essential metals (Table 10.1) are commonly found as natural constituents in proteins where they perform a wide spectrum of specific functions associated with biological processes. Metalloproteins with catalytic properties, metalloenzymes, implement chemical transformations of certain substrate molecules, and almost half of all enzymes in the human organism depend on the presence of one or more metal ions. Obviously, these metal ions are key pharmaceutical targets for drugs.

Pharmaceuticals may control metabolism of essential elements in two ways:

1. Supply of specific drugs with target properties may enable delivery or removal of elements to/from specific sites.

2. The natural physiological pathways may be blocked by the drug.

Nonessential (or toxic) elements can be useful in medicine since they either show insignificant toxic effect in a certain limited concentration range (left-hand side of Figure 10.1) or because their pharmaceutical benefit overrules their toxic effect. Such compounds are potentially of pharmacological interest, e.g., in killing certain cell types, as cancer cells or microorganisms while only expelling minor harm to the host. The examples include drugs based on platinum, gold, antimony, and bismuth complexes, which are described in more detail in Section 10.6. Their toxicity depends on concentration, oxidation state, and ligand and thus should be administered

TABLE 10.1

Constitution of the Human Organism (Adult 70 kg)

Recommended Recommended

TABLE 10.1

Constitution of the Human Organism (Adult 70 kg)

Recommended Recommended

Element

Mass (g)

Daily Dose (mg)

Element

Mass (g)

Daily Dose (mg)

Oxygen

45,500

Copper

0.11

3-5

Carbon

12,600

Aluminum*

0.1

Hydrogen

7,000

Lead*

0.08

Nitrogen

2,100

Antimony

0.07

Calcium

1,050

800-1200

Cadmium*

0.03

Phosphorous

700

800-1200

Tin*

0.03

Sulfur

175

10

Iodine

0.03

0.15

Potassium

140

2000-5500

Manganese

0.03

2-5

Chlorine

105

3200

Vanadium*

0.02

Sodium

105

1100-3300

Selenium

0.02

0.05-0.07

Magnesium

35

300-400

Barium*

0.02

Iron

4.2

10-20

Arsenic*

0.01

Zinc

2.3

15

Boron*

0.01

Silicon

1.4

Nickel*

0.01

Rubidium*

1.1

Chromium

0.005

0.05-0.2

Fluorine

0.8

1.5-4.0

Cobalt

0.003

0.2

Bromium*

0.2

Molybdenum

<0.005

ca. 0.1

Strontium*

0.14

Note: Elements marked with * are either nonessential, or their function is unknown.

Note: Elements marked with * are either nonessential, or their function is unknown.

Beneficial

Beneficial

Harmful

FIGURE 10.1 Dose/effect diagram. Response to (A) nonessential or toxic and (B) essential elements. Note that at sufficiently small concentrations, toxic compounds are tolerated, while essential elements become toxic at elevated concentrations.

Harmful

FIGURE 10.1 Dose/effect diagram. Response to (A) nonessential or toxic and (B) essential elements. Note that at sufficiently small concentrations, toxic compounds are tolerated, while essential elements become toxic at elevated concentrations.

with utmost care. This underlines the major point: "Specific biological activity of inorganic compounds can be achieved by proper design."

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