L02_water_2013_462a

The hydrophobic eect hydrophobic eect the oil drop

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Unformatted text preview: Polar groups form hydrogen bonds with water •  Water is strong dipole •  Good solvent for Ions/ molecules with charged groups and polar groups The Hydrophobic Effect •  hydrophobic effect, the "oil drop" effect •  associaHon of non ­polar groups with each other in aqueous systems •  MinimizaHon of contact between water and nonpolar solutes •  hydrophobic means “water ­haHng” •  misnamed “hydrophobic interacHons“ Amphipathic Molecules •  Amphipathic molecules –  contain polar and nonpolar regions –  polar region tends to be exposed to water –  nonpolar region tends to cluster together polar nonpolar minimize solvent exposed surface Biological Importance •  Many biomolecules are amphipathic –  proteins, certain vitamins, lipids, etc. –  hydrophobic interacHon between lipids and protein determines the structure of membranes Hydrogen Bonds: Not just for water •  Between O ­H or N ­H groups and O or N •  DirecIonal: there is a preferred geometry Hydrogen Bonds in Biomolecules •  H ­bonds help determine the structures of biomolecules •  Protein secondary structure •  DNA base pairing ElectrostaHc InteracHons •  Also called Ionic InteracIons •  Coulomb’s Law: charges Force of interacHon Q1Q2 F= 2 "r distance between dielectric constant 1 for vacuum ≈2 for hexane 4–10 in proteins ≈80 for H2O F r charged atoms Q: Is the a7racHve force between two oppositely charged ions greater in water or in protein? The Hydrophobic Effect •  hydrophobic effect, the "oil drop" effect •  associaHon of non ­polar groups with each other in aqueous systems •  MinimizaHon of contact between water and nonpolar solutes •  hydrophobic means “water ­haHng” •  misnamed “hydrophobic interacHons“ Nonpolar molecules interfere with water H ­bonding •  Unfavorable interacHon •  Water reorganizes into ordered cages around the solute The hydrophobic effect is entropic More dissolved...
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