Lecture of 22 January 2020 (no lecture 20 January - MLK day)Outline of today's lecture

Statistical factors and cooperativity•Dicarboxylic acids and cooperativity •Activities•

Ka KanH2A F HA a f Eady

CHAIHut CA

Ht Ht

Gta CHA CA

Oxalic acidi correctedi figure from A02C COzHi i

lecturepka pka pka 1.23

pKa 4.19

species CHA ITA At

termini 1 Kathy Kaikaydenominator Ht

KaObs 910 oxalic acid

Kaiexpect za 4 for identical independent sites

carboxylate groups are notindependent

4 statistical factor

Useof Kafka to probe interaction betweenbinding sites

start with I E tyt2 Ya

at 2

3 examples with b

Hua Htt Ai KafkaCHA7µACAA 0 100 0 as

B 50 O 50 O

C 251 50 25 4

CA negative cooperative ETS 4

CB positive coops all or none a 41Cc stathstead behaviors K 4

caution the significanceof theratio depends on how K's are defined

Di protec vs monoprotec acid

conc 2 Co of monoprotic and with 1 carboxylgroup

in s ka dissoc constf It YET

Hw diprotic acid with 2 carboxyIs in a

singlehypotheticalmolecule identicalhw and independent non interactingConc Co

twoa E FETsttEIT.TK lgdcssoc

z constants

at E YYIthese two expressions ka 2 kafor h are equivalent if ka bag 4

check

ti i ii Idenomination for n idential independent sites

Gthft a ltnckjgxnhzDlehf.ITa r

It Effy KaikanHDL X

n n

dicarboxylic

tHAC CCHDncouH

O H oy Itami Y5

ka C C Ka foroxalica vO O andmalonicacids

Ka 2haka r n

Hoy CHIN Cont HEC Cata nKau

Hae CHIN WI E 02C CCHulu CdiCr

solvation repulsionG for firststep cdeprotonation

Gz for secondstep t Get

Ge 1389 22Ga G Tree Hml

ha Kayz ka 2 Kar

RThrkaz t RTlnkal Geta RT en Koe

4kg Get

originally analyzedby John Kirkwood

1389 GI Empiricalmodelinge CA Fitofc Coulomb's

RTenkai4km law type equationE 50

with effective dielectricconstant 50water 80

n

r 1.33n t 2 CA separation betweenchargesas a

functionof h GACS111,8238194

Activitiesnon idealeffects important for chargedmolecules

H Ac Htt Ai pKa 4.75additionof NaCl Nat Ce

shifts equilibrant rightandlowerspKaaccurate description at low concestneyk

Ht Ai concentrationKa HAC

Koi activitiesAHAc A 3 C

Ht Ai 7 2 5It t ka

non idealeffects