Water and Buffers
Water is the medium for life
• Organisms typically contain 70–90% water.
• Dissolve nutrients and easy to transport
• Chemical reactions occur in aqueous environment
• Water is a critical determinant of the structure and function of
proteins, nucleic acids, and membranes
Structure of the Water Molecule
• There are four electron pairs around an oxygen atom in water
• Two of these pairs covalently link two hydrogen atoms to a central
oxygen atom
• The two remaining pairs remain nonbonding (lone pairs)
• The water molecule is a polar molecule: the opposite ends have
opposite charges
• Polarity allows water molecules to form hydrogen bonds with each
other
• The electronegativity of the oxygen atom induces a net dipole moment
– O is more electronegative than H, shared electrons are pulled more
towards O.
– Because of the dipole moment, water can serve as both a hydrogen
bond donor and acceptor
, Hydrogen Bonding in Water
• Strong dipole-dipole or charge-dipole interaction that arises between
an acid (proton donor) and a base (proton acceptor)
• Typically involves two electronegative atoms (frequently nitrogen and
oxygen)
• Hydrogen bonds are strongest when the bonded molecules are
oriented to maximize electrostatic interaction
• Ideally the three atoms involved are in a line
Water is the medium for life
• Organisms typically contain 70–90% water.
• Dissolve nutrients and easy to transport
• Chemical reactions occur in aqueous environment
• Water is a critical determinant of the structure and function of
proteins, nucleic acids, and membranes
Structure of the Water Molecule
• There are four electron pairs around an oxygen atom in water
• Two of these pairs covalently link two hydrogen atoms to a central
oxygen atom
• The two remaining pairs remain nonbonding (lone pairs)
• The water molecule is a polar molecule: the opposite ends have
opposite charges
• Polarity allows water molecules to form hydrogen bonds with each
other
• The electronegativity of the oxygen atom induces a net dipole moment
– O is more electronegative than H, shared electrons are pulled more
towards O.
– Because of the dipole moment, water can serve as both a hydrogen
bond donor and acceptor
, Hydrogen Bonding in Water
• Strong dipole-dipole or charge-dipole interaction that arises between
an acid (proton donor) and a base (proton acceptor)
• Typically involves two electronegative atoms (frequently nitrogen and
oxygen)
• Hydrogen bonds are strongest when the bonded molecules are
oriented to maximize electrostatic interaction
• Ideally the three atoms involved are in a line
