Polarity

•Solubility due in large part to polarity of solvent

•Three categories:

  1-   Polar (water) acts as a solvent according to the following mechanisms:

  a) Dielectric constant:

 due to their high dielectric constant, polar solvents reduce the force of attraction between oppositely charged ions in crystals.

Example: water possessing a high dielectric constant (> = 80) can dissolve NaCl, while chloroform (> = 5) & benzene (> = 2) cannot. Ionic compounds are practically insoluble in these 2 solvents.

Expression of Solubility

•Percent solubilities:

  --%w/v  g/100 ml solution

  --%v/v  ml/100 ml solution

  --%w/w  g/100 g solution

General Rules of Solubility

•Inorganic (examples)

  1. If both the cation and anion of an ionic compound are monovalent, the solute-solute attractive forces are usually easily overcome, and therefore these compounds are generally water soluble (NaCl, LiBr, KI)

  2. If both the cation and anion are multivalent, the solute-solute interaction may be too great to be overcome by the solute-solvent interaction and the compound may have poor water solubility (CaSO4, BaSO4)

  3. Salts of alkali metals (Na, K, Li) – usually water soluble

 

Properties of Liquid Solutions

•Homogenous mixture with uniform properties throughout

•The solute cannot be isolated from the solvent

•The particle size of the solute is about the same as that of the solvent

•All of the molecules of the solute and solvent are intimately mixed

•The continuous particle motion in solution maintains the homogenous, random distribution of the solute and solvent particles

•Volumes of solute and solvent are not additive

–Adding 1 L of alcohol and 1 L of water does not equal exactly 2 L of solution.

•The volume of pure liquid is determined by the way in which the individual molecules fit together

•When two or more kinds of molecules are mixed together, the molecular interactions become more complex:

•solvent interacts with solvent

•solute interacts with solvent

•solute may interact with another solute

Normality (N)

•Frequently used for acids and bases

•A function of number of H+ per mole of acid or OH- per mole of base

•Formula:

•N = (Molarity) the number of H+ or OH-         mole

•Units: normal = N

•

Molarity (M)

•Formula:

  M = moles of solute

         liters of solution

•Units: moles per liter (mol/L); millimoles per liter (mmol/L); micromoles per liter (μmol/L)

Solvent

•The component present in largest quantity

•When water is the solvent, the homogenous mixture solution is referred as aqueous

–Latin aqua = water

Supersaturated Solution

•Excess solute may remain in solution for a time before precipitation

•Inherently unstable

•With time excess solute will precipitate and the solution will revert to a saturated solution

Solubility

•Solubility:

 Concentration of a solute in a saturated solution at a given temperature

•Saturated Solution:

 When a solvent at a certain temperature has dissolved all of the solute that it can

•Supersaturated Solution-- Crystallization

The solubility of a pure chemical substance at a given temperature and pressure is constant (USP, Merck)--However, its RATE of Solution depends on the particle size of the substance and the extent of agitation

•Solubility given usually as “1 gram in X ml” of water, alcohol, etc.

•

Echinocandins

Caspofungin از این دسته میباشد، در درمان کاندیداهای مقاوم  به وریکونازول و پوساکونازول از اکینوکاندینها استفاده میکنیم که

اثر خیلی خوبی در درمان عفونتهای کاندیدایی دارند. درمان انتخابی candidiasisInvasive اکینوکاندینها میباشند؛

Invasive candidiasis مانند: 

1 ) کاندیدمیا که در بیماران ICU رایج است.