Mode of Action of Dyes Flashcards
Define electrostatic (ionic) binding.
Electrostatic binding is the attraction between anionic auxochrome groups in dyes and cationic end-groups in tissue and vice versa.
What type of bonding do basic dyes use?
Basic dyes use electrostatic binding to attach themselves to tissue. Their cationic auxochrome groups bind to anionic components in tissue.
What does it mean if tissue is described as basophilic?
Basophilic means that the tissue is readily stained by basic dyes. This means the tissue will have anionic (acid) end-groups.
How do acid dyes attach themselves to tissue?
Acid dyes have an anionic auxochrome which binds electrostatically to cationic (basic) end-groups in tissue.
What is meant by the term acidophilic?
Acidophilic refers to tissue which is readily dyed by acid dyes. This tissue will have basic (cationic) end-groups which bind to anionic (acid) groups in the dye.
What is an amphoteric dye? Give an example.
An amphoteric dye contains positive and negative chargeable groups, which makes it cationic (basic) below a specific pH and anionic (acid) above that pH. This pH is called the dye’s iso-electric point. An example of an amphoteric dye is Celestin Blue B.
What is a neutral dye? Give an example.
Neutral dyes are a colloidal solution of acid and basic dyes which is soluble in methanol. Neutral dyes have an affinity for both acidophilic and basophilic tissue components. The Giemsa stain contains the acid dye, Methylene Blue, and the basic dye, Azure B.
Give an example of a dye which uses ionic binding to attach itself to tissue.
What are the types of non-ionic binding dyes can use to attach themselves to tissue?
Hydrogen bonding, Van der Waals forces and covalent bonding.
What is hydrogen bonding?
Hydrogen bonding is formed between hydrogen and a oxygen or nitrogen.
Give an example of a stain that uses hydrogen bonding.
Best’s Carmine uses hydrogen bonding to bind to glycogen.
What are Van der Waals forces?
Van der Waals forces are weak attractions between the electrons of one atom and the nucleus of another. When many Van der Waals forces occur, the binding force can become strong. This strong binding force only occurs if tissue and dye have exactly complementary surfaces to bring their atoms close enough to form the Van der Waals bonds. It is believed that Trichrome stains bind using Van der Waals forces.
What are covalent bonds?
A covalent bond forms when two non-metal atoms share a pair of electrons between them. Covalent bonds are very strong and not easily broken. Covalent bonds are not involved in most staining reactions. The PAS reaction involves covalent bonding between chromogens and tissue reaction groups.
