L1: Water: the "universal" solvent

what makes water the “universal” solvent

1. nearly all biological molecules assume their shapes and functional properties based on their interactions w water

2. the “solvent” for most biochemical reactions is water, and metabolites depend on water for their transport in vivo

3. water is catalytically involved in many biochemical reactions

OH- acts as electron -

donor

H+ acts as an electron -

acceptor

in most biochemical reactions

• when water is a reactant, the reaction is called -

• when water is product, the reaction is called -

hydrolysis, dehydration/condensation

angular geometry results from - nature of H2O

polar

four hybrid sp3 electron orbitals of oxygen form a -

• two orbitals represent the - electrons of of oxygen

• other two orbitals represent the - electrons between O and H

tetrahedron, unshared, shared

oxygen, with its 2 pairs of -, is electronegative and the H atoms carry a net - charge

this creates an -

unshared electrons, positive, electrical dipole

water molecules orient themselves according to their - and hydrogen bonds form between a - H and - O in adjacent water molecules

electric dipole, donor, acceptor

H bonds between adjacent molecules give water its strong - and unique properties (ex. - melting, boiling, vaporizing temperatures)

internal cohesion, high

in ice, each water molecule H bonds with - other water molecules, forming -

this is the reason why water - upon freezing

four, hexagonal lattices, expands

liquid water does not possess the static hexagonal structure of ice but it is still -

strongly cohesive

theoretical and spectroscopic data suggests that liquid water forms between - membered H bonded rings

3-7

water H-bonded to what?

hydroxyl functional groups

water H-bonded to what?

carbonyl functional groups

water H-bonded to what?

carboxylate functional groups

water H-bonded to what?

amino functional group

water dipole is able to interact with both - and -

anions, cations

when water molecules surround an ion, they - the attractive forces between opposite ions and keep them -, which is why - dissolve readily in water

weaken, apart, salts

the strength of multiple water:ion bonds compensates for the energy used to break - between water molecules

hydrogen bonds

like water, carbon dioxide bonds also form dipoles and can orient themselves via weak - interactions called -

electrostatic, permanent dipoles

dipole of a polar molecule can induce a dipole in an, otherwise, neutral molecule by attracting electrons toward the dipole

higher negative exponent, the higher affinity

weakest VDW form when complementary dipole moments occur in - molecules

non-polar

strength of chemical bonds

covalent » ionic > h bond > polar VDW > non-polar VDW

non-polar/hydrophobic molecules added to water do not -

this is because they are unable to form - or - bonds with water

instead, water molecules form - bonds between themselves around the non-polar solute

dissolve

ionic, hydrogen

hydrogen

clustering of non-polar solutes is driven by the thermodynamic properties of water = -

hydrophobic effect

delta G = -

if delta G is negative, reaction/interaction can occur -

negative delta G means reaction or interaction is energetically -

free energy change

spontaneously

favourable

delta H = - change in making or breaking bonds

generally forming bonds yields - delta H and breaking bonds - delta H

negative delta H favours reaction or interaction by making delta G more -

enthalpy

negative, positive

negative

delta S = change in relative order of reactants and products = -

increase in disorder = - delta S, favours reaction or interaction

- delta S decreases delta G

entropy

positive

positive

increase in - increases delta S, lowers delta G

temperature

it is always unfavourable to have - solutes in water

non-polar

water becomes more - around the non-polar solute → - in entropy

despite reduction in entropy, clustering of non-polar solutes occurs because the same volume of solutes can be “caged” by a - surface area of water

ordered, decrease

smaller

structure of macromolecules is driven by the -

hydrophobic effect