Water and Buffer

• Water content varies in different body organs and tissues.
• Water content can be little as 8% in teeth to 85% in brain.
• *About 60% of humans is water.
• Water is the principal component of most cells
• The electronic structure of H2O is tetrahedral: 2 Covalent bonds with H atoms and 2 sets of unpaired electrons = Polar Molecule
• Polar - Molecule with positive and negative ends.
• • Highly cohesive (H-bonding Interactions)
  • One H2O molecule can H-bond with 4 others (depends on temperature)
  • Lifetime on the order of picoseconds, water molecules are nearly constant in motion.
• Water in a solid is less dense than liquids
• Liquid at room temperature
• Expands as it solidifies and becomes very porous and therefore ice floats.
• • High surface tension
  • Water molecules on the surface can only interact with molecules beside and below them, in order to equalize, they have stronger interactions with molecules beside them, creating surface tension.
• It has 2 different ends and depending on the environment, it can use either the negative or the positive end to interact or bind to different molecules.
• Dielectric constant

  • "dia (through) -electric"
• Dialectric constant

  Measure of a solvent's ability to decrease electrostatic attraction of ions
• Dialectric constant

  Measure of effectiveness as an insulator of charge.
• High dielectric constant of water means better solvation by water - better hydration
• Solvation - Process of surrounding solute particles with solvent molecules.
• Hydration - Process of surrounding solute particles with water molecules.
• TYPES OF BONDS: 

  1. Ionic Bonding
  2. Covalent bonding

  • Polar
  • Non-polar

  1. Non-Covalent Bonding

  • Hydrogen Bonding
  • Ionic Interactions
  • Hydrophobic Interactions
  • Van Der Waals Interactions
• 4 TYPES OF NON-COVALENT INTERACTIONS

  1. Hydrogen Bonds 2. Ionic Interactions 3. Hydrophobic Interactions 4. Van der waals interactions
• • he atoms are Dipoles - partial charges due to unequal sharing of e-
  • Dipoles can align to form H bond
  • Has some covalent character (directionality)
• 1. Hydrogen Bonds
  2. Between Neutral Groups
  3. Between Peptide bonds
• 1. Ionic Interactions 
  2. Attraction- possible when there are 2 opposite charges in ions.
  3. Repulsion- possible when there are 2 similar charges in ions.
• 1. Hydrophobic Interactions
  2. Can be seen in compounds which are mainly Hydrocarbons (consists of hydrogen and carbon.)
  3. Does not interact with water.
• 1. Van der waals interactions

  • Weakest attractions between 2 atoms in close proximity.
• 1. Ionic Interactions 
  2. Attraction- possible when there are 2 opposite charges in ions.
  3. Repulsion- possible when there are 2 similar charges in ions.
• • Weaker bonds are easily broken and reformed which are vital for molecular dynamics of life.
• • ARRHENIUS
  • Dissolving a substance on an aqueous solution (water is present)
  • Acids and Bases will be determined on what is released in the reaction.
• • Acid
  • Increase of hydronium ions (H+ / H3O+). 
  • Dissociates into anions and releases high concentrations of protons/hydronium ions in the solution.
• • BRONSTED-LOWRY
  • Water is not a required medium, it focuses on protons.
• • Bronsted–Lowry ACIDS, donates protons
• Bronsted–Lowry BASES, receives protons
• Reactant side:

  H2O = ACID, loses the proton

  NH3 = BASE, gains the proton
• Conjugate Acid-Base Pairing
• Lewis Base, donates electron pairs
• • WATER is amphoteric
  • Can act as both acid and base.
• Strong Acids

  • COMPLETELY dissociates into ions causing a significant drop in pH.
• • Weak Acids
  • PARTIALLY dissociates into ions.
  • Does not release all the H⁺ ions to the solution.
• pH (potential of Hydrogen)

  • Quantitative measure of acidity and basicity of a substance.
• Buffers resist drastic changes in pH when small amounts of strong acids or bases are added.