A complex ion is a metal ion bonded to one or more Lewis bases. We have seen that a characteristric property of
metal ions is their ability to act as Lewis acids by attracting nonbonding electron pairs of water molecules. Some
metal ions also commonly attract the nonbonding pairs of other Lewis bases, such as ammonia molecules and
hydroxide ions, to form complex ions. The following table illustrates the formation of some common complex
ions. A rough rule of thumb that works about 75% of the time is that the number of Lewis bases (called ligands)
that a given metal ion attracts is equal to double its positive charge.
Biological Importance of Coordination Complexes
The ability of metal ions to coordinate with and release ligands and to easily undergo oxidation and reduction
makes them ideal for use in biological systems. Metal ion complexes are used in humans for the the transport and
storage of oxygen, as electron transfer agents, as catalysts and as drugs. The 1 row transition metals are essential
for human health.
Cr – assists insulin in controlling blood sugar, cholesterol
Mn – needed for several enzymatic reactions
Fe – component of hemoglobin and myoglobin, involved in electron transport chain
Co – component of vitamin B12, which is essential for the metabolism of carbohydrates, fats and proteins
Ni – component of enzymes urease and hydrogenase
Cu – component of several enzymes: assists in iron storage; involved in the production of color pigments of hair,
skin and eyes
Zn - component of insulin and many enzymes
Iron in Blood
In mammals, the principle source of energy comes from the oxidation of carbohydrates, proteins and fats.
Although oxygen is the oxidizing agent for these processes, it does not react directly with theses molecules.
Instead, electrons from the breakdown of these nutrients are passed along a complex chain of molecules, called
the respiratory chain, eventually reaching the O2 molecule. The principal electron- transfer molecules are iron-
containing cytochromes, consisting of two parts: an iron complex – heme and a protein. The iron is coordinated to
a ligand called a porphyrin. (In plants – chlorophyll is a porphyrin complex of Mg )
In addition to electron transfer, iron also plays a principle role in transport and storage of oxygen. Hemoglobin
molecule (made from heme complex and protein) can bind four O2 molecules forming a bright red complex. When
the oxygen molecule is released, water molecules occupy their coordination position around the Fe giving the
blood a bluish tint.
In some people, in the synthesis of the proteins needed for hemoglobin, an improper amino acid is inserted into
the protein in two places. This changes the polarity and the hemoglobin changes shape from a disk-shaped to a
sickle-shape. The misshapen cells can aggregate and get stuck in capillaries, causing a condition called sickle cell
CO and CN are both very good ligands toward iron and can interfere with the normal workings of iron complexes.
Carbon monoxide has about 200 times the affinity for the iron ion in hemoglobin than oxygen does. The resulting
stable complex, carboxyhemoglobin, prevents the normal uptake of O 2. Asphyxiation can result if enough carbon
monoxide is present in the air.
Cyanide coordinates to and iron containing cytochrome enzyme that catalyzes the oxidation-reduction reactions
of certain cytochromes. The coordinated cyanide prevents the electron-transfer process and rapid death results.
Cyanide is called a respiratory inhibitor.
There are many individual metals causing varying degrees of illness based on acute and chronic exposures. Heavy
metals is the term used for a group of elements that have particular weight characteristics. They are on the
"heavier" end of the periodic table of elements. Some heavy metals - such as cobalt, copper, iron, manganese,
molybdenum, vanadium, strontium, and zinc - are essential to health in trace amounts. Others are non-essential
and can be harmful to health in excessive amounts. These include cadmium, antimony, chromium, mercury, lead,
and arsenic - these last three being the most common in cases of heavy metal toxicity.
Causes & Development
Sources of toxicity can include environmental, water supply, industrial, hobbies, and others, thus a full history of
the person's work and living habits can help pinpoint potential heavy metal sources.
Causes of arsenic toxicity include ingestion of arsenic (found in insect poisons), skin contact (e.g. some linseed oils)
and even drinking water.
Signs & Symptoms
As an example of the scope of a heavy metal's toxicity, lead can affect the nervous system, gastrointestinal system,
cardiovascular system, blood production, kidneys, and reproductive system.
Symptoms of heavy metal toxicity include mental confusion, pain in muscles and joints, headaches, short-term
memory loss, gastrointestinal upsets, food intolerances/allergies, vision problems, chronic fatigue, and others. The
symptoms are so vague that it is difficult to diagnose based on symptoms alone.
Symptoms include nausea or vomiting, abdominal pain, diarrhea, garlic odor on breath, excessive salivation,
headache, vertigo, fatigue, paresthesia, paralysis, kidney failure, progressive blindness, and mental impairment.
Signs include mottled brown skin, hyperkeratosis (increased pigmentation) of palms and soles, cutis edema,
transverse striate Leukonychia, perforation of nasal septum, eyelid edema, coryza, limb paralysis and reduced
deep tendon reflexes. Mental symptoms include apathy, dementia, and anorexia.
Signs and Symptoms include combinations of gastrointestinal complaints, hypertension, fatigue, hemolytic anemia,
abdominal pain, nausea, constipation, weight loss, peripheral neuropathy, cognitive dysfunction, arthralgias,
headache, weakness, convulsions, irritability, impotence, loss of libido, depression, depression of thyroid and
adrenal function, chronic renal failure, gout. A patient with lead poisoning may have a combination of symptoms -
or no symptoms at all until the condition has progressed. Mental symptoms include restlessness, insomnia,
irritability, confusion, excitement, anxiety, delusions, and disturbing dreams.
Mercury toxicity has been linked to, among other things, mercury dental fillings, particularly when people have a
large number of them. Symptoms include a metallic taste in the mouth, excess salivation, gingivitis, tremors,
stomach and kidney troubles. Mental symptoms include shyness, irritability, apathy and depression, psychosis,
mental deterioration, and anorexia.
Treatment & Prevention
The first step in treating any heavy metal toxicity is to identify the toxic elements and begin the removal process.
The easiest screening process is a Hair Analysis. Additional testing involves the use of chelating drugs along with a
24-hour urine collection to determine levels of heavy metals. From here, treatment is based on the individual and
will usually involve the use of metal chelating drugs or intravenous EDTA chelation. For many patients, intravenous
Vitamin C and replacement mineral infusions are also recommended to support the body through the metal
removal process. Once laboratory tests indicate that the heavy metals are undetectable, treatment is considered
complete. Often many - if not all - symptoms previously experienced will have resolved, though some may linger,
indicating residual damage to organ systems. Therapies can then be targeted to these systems and any specific
Symptoms will often begin to improve within weeks or even days of commencing treatment. Therapy may last
from 6 months to 2 years.
Signs, symptoms & indicators of Heavy Metal Toxicity:
Lab Values - Cells Microcytic red cells
Lead poisoning can lead to the formation of small red blood cells.
Lab Values - Chemistries High serum iron
Elevated serum iron can occur in cases of lead poisoning.
Symptoms - Head - Vision disturbances
Symptoms - Nails Moving white lines across nails
Mees' Lines (transverse white lines) are a sign of arsenic poisoning.
Symptoms - Nervous Numb/tingling/burning extremities
Symptoms - Skeletal Joint pain/swelling/stiffness
Symptoms - Sleep Drowsiness
Chelating for removal of heavy metals
Chelation therapy using EDTA is the medically accepted treatment for lead poisoning. EDTA is injected
intravenously and once in the bloodstream, it traps lead and other metals, forming a compound that the body can
get rid of in the urine. The process generally takes between 1 - 3 hours. Other heavy metal poisonings treated with
chelation include mercury, arsenic, aluminum, chromium, cobalt, manganese, nickel, selenium, zinc, tin, and
thallium. Chelating agents other than EDTA are also used to clear several of these substances from the
Heavy metal toxicity in humans has been associated with many health conditions, including heart disease,
attention deficit/hyperactivity disorder (ADHD), Alzheimer's disease, immune system disorders, gastrointestinal
disorders (including irritable bowel syndrome or IBS), and autism