Water buffer

Water: The Medium of Life

  • Presented by Champion Deivanayagam, Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham.

Outline for Lecture

  • Topics Covered:

    • Properties of water

    • pH and its significance

    • Buffers: Definitions and functions

    • Unique role of water in environmental fitness

Quotes about Water

  • "If there is magic on this planet, it is contained in water." - Loren Eisley

  • Key Idea: Water is essential to life, highlighting its significance in biological processes.

Essential Question

  • What properties of water make it uniquely suited for its role as the medium for life?

Unusual Properties of Water

  • Physical Properties:

    • High boiling point, melting point, and heat of vaporization.

    • High surface tension due to hydrogen bonding.

    • Water's bent structure contributes to its polarity.

    • Non-tetrahedral bond angles enhance its molecular interactions.

    • Water can form up to four hydrogen bonds per molecule.

Structure of Water

  • Geometric Considerations:

    • Tetrahedral angle is 109 degrees; in water it's about 104.3 degrees due to molecular arrangement.

    • Structural representation: Two hydrogen atoms bonded to an oxygen atom, showcasing partial charges (+ on H, - on O).

    • Covalent bond length: Oxygen-hydrogen bond ~0.095 nm; van der Waals radii measure 0.14 nm (O) and 0.12 nm (H).

Water Molecules and Hydrogen Bonds

  • In Ice:

    • Four hydrogen bonds per water molecule; bond lifetime ~10 microseconds.

  • In Liquid Water:

    • Average 2.3 hydrogen bonds per molecule; bond lifetime ~10 picoseconds.

  • Molecular Fluctuations:

    • Water has areas of ordered (tetrahedral) and disordered arrangements, affecting physical behavior.

Solvent Properties of Water

  • Ionic and Polar Solutes:

    • Water excels as a solvent due to its polarity, facilitating hydration shells around ions.

    • Highly polar nature allows it to dissolve salts, sugars, and other polar molecules.

  • Hydrophobic Interactions:

    • Nonpolar solutes induce structural changes in water, increasing its order and decreasing entropy.

    • Amphiphilic molecules, which interact with both polar and nonpolar environments, help stabilize cellular structures.

Micelle Formation and Buffer Systems

  • Amphiphilic Behavior:

    • Micelles form in aqueous solutions, crucial for biological membranes and cellular processes.

  • Osmotic Pressure and Colligative Properties:

    • Colligative properties include freezing point depression and osmotic pressure, significant for cellular function and pharmaceutical applications.

pH and Ionization of Water

  • Water Ionization:

    • Water can dissociate into H+ and OH- ions, influencing its electrical conductivity.

    • The ion product constant of water (Kw) relates H+ and OH- concentrations in solution.

  • Understanding pH:

    • pH scale introduced by Soren Sørensen allows easy reference to hydrogen ion concentration.

    • pH is defined as the negative logarithm of [H+]. For example, when [H+] = 1 x 10 -7 M, then pH = 7.

Electrolytes and Their Properties

  • Strong Electrolytes:

    • Fully dissociate in water, raising electrical conductivity (e.g., NaCl, HCl).

  • Weak Electrolytes:

    • Partially dissociate; characterized by the acid dissociation constant (Ka) and Henderson-Hasselbalch equation for pH calculations.

Buffer Systems in Biological Systems

  • Importance of Buffers:

    • Resist changes in pH crucial for maintaining cellular environment stability.

  • Major Buffer Systems:

    • Phosphate Buffer System: Operates in physiological pH, helps maintain cellular fluid pH.

    • Histidine Buffer System: As an amino acid, histidine contributes to buffering through its imidazole side group.

    • Bicarbonate Buffer System: Main buffer in blood plasma; balances acid-base changes via carbonic anhydrase.

Summary of Key Water Properties

  • Water's unique properties, predominately driven by hydrogen bonding, make it essential for biological functions.

  • Its capability to dissolve various substances and its role in maintaining pH are vital for life.

  • Buffer systems effectively mitigate pH fluctuations, supporting metabolic and enzyme functions in biological systems.