BB450 Water and Hydrogen Bonds PDF

Water and Hydrogen Bonds BB450 Tetrahedral Geometry of Carbon  The electronegativity of select elements Element Electronegativity Oxygen 3.5 Nitrogen 3.0 Sulfur...

Water and Hydrogen Bonds BB450 Tetrahedral Geometry of Carbon  The electronegativity of select elements Element Electronegativity Oxygen 3.5 Nitrogen 3.0 Sulfur 2.6 Carbon 2.5 Phosphorous 2.2 Hydrogen 2.1 Electronegativity: The tendency of an atom to attract electrons to itself in a chemical bond. The higher the electronegativity, the stronger the attraction for electrons.  Water is highly polar Unequally sharing of electrons due to a difference in electronegativity of the oxygen and hydrogen atoms gives rise to partial negative and positive charges Polar nature of water largely determines its solvent properties Dissolves polar compounds; interacts strongly with self Hydrogen bonding between polar groups and water The partly positive hydrogen (H-bond donor) atom bonded to a very electronegative atom interacts with a lone pair of electrons on an electronegative (H-bond acceptor) atom Hydrogen bonding between nucleotides Hydrogen bonds are important for many biological molecules  Oxidation/Reduction Reactions Reduction - Gain of electrons Oxidation - Loss of electrons H3CHC=O + NADH + H+ H3CH2COH + NAD+ Spontaneity of life processes and free energy All biochemical processes occur “spontaneously” Determined by the Gibbs free energy change: ∆G = ∆H - T∆S If ∆G = 0 reaction is at equilibrium If ∆G < 0 reaction will occur spontaneously (forward) If ∆G > 0 reaction will not occur spontaneously  Hydrophilic & Hydrophobic Substances Hydrophilic (water-loving) compounds readily dissolve in water Hydrophobic (water-fearing) compounds readily separate from water Hydrophilic Hydrophobic Ionic compounds like NaCl Nonpolar hydrocarbons like hexane Polar organic compounds like alcohols, ketones, or Lipids like fat and cholesterol carbonyls Weak acids like phosphates and amino acids Sugars/carbohydrates Hydrophobic effects are crucial for life, including the formation of folded proteins, nucleic acids (DNA, RNA), and membranes.  Amphipathic substances Amphipathic (both feeling) or amphiphilic (both loving) compounds have distinct polar (water soluble) and non-polar portions Example: a fatty acid Soap’s amphipathic molecules form micelles in water Micelle: a spherical (clustered) arrangement of amphipathic molecules in water hydrophobic parts cluster away from water hydrophilic parts are face out and contact the water Soap micelles trap non-water soluble oils and grime in its core Phospholipid bilayers are the basis of membranes General term is phospholipid Main component is phosphoglycerides Tails 16 - 18 carbons long Compositions vary Asymmetric Self-sealing Liposomes Liposomes: artificial vesicles Water soluble drugs go in core Fat-soluble drugs go in lipid bilayer Surface sugars prevent destruction by the immune system Liposomes can be prepared with targeting proteins on surface and drug inside to deliver drug to specific cells Protein folding based on hydrophobicity  Bond energies and strength Type of Bond Bond Energy (kJ/mol) Covalent Bonds C—H 413 O—H 460 Noncovalent Bonds Hydrophobic 4-12 Interaction Hydrogen Bond 20 Ion-dipole Interaction 20