1

1. Why a metal ion and not a molecule?

2. Why a main group or a transition metal ion?

1. Why a metal ion and not a molecule?

demo: balloon + water

somethingpolarizable

+ H H

O

somethingpolarizable

1. Why a metal ion and not a molecule?

demo: balloon + water

somethingpolarizable

+ H H

O

somethingpolarizable

1. Why a metal ion and not a molecule?

2. Why a main group or a transition metal ion?

2

Write electron configurations for

Ca2+ in CaSOCaSOCaSO444

Al3+ in AlAlAl222OOO333

Cu2+ in CuSO4

Cr3+ in Cr2O3White SandsNatl. Mnmt.

CaSO4

Open Open vsvs closed shellclosed shell

O2- O2-

O2-

O2- O2-

Al3+

O2-

Cr2O3 AlAlAl222OOO333

[Ne]Cr3+

[Ar]3d3

Environment mattersEnvironment matters

O2- O2-

Cr3+

O2-

O2- O2-

Al3+

O2-

Cr2O3 AlAlAl222OOO333

Cr3+

Environment mattersEnvironment matters

O2- O2-

Cr3+

O2-

O2- O2-

Cr3+

O2-

Cr2O3 AlAlAl222OOO333

http://www.mineralminers.com/html/rbygems.stm

Demo: Fe3+(aq) and H+, SCN-

3

1. Why a metal ion and not a molecule?polarizing influence

2. Why a main group or a transition metal ion?open vs closed shellenvironmental control

• Why a metal ion and not a molecule?

• Why a main group or a transition metal ion?

• Polarizing ability (charge density)

• Mn+ as Lewis acids (esp. Zn2+)

• Heme: common theme, tunable environment

• Redox: (e- but sometimes not H+ transfer)

• Transport, storage

Compare radiiCompare radii

K+ Ca2+

Na+ Mg2+

Zn2+Fe2+Mn2+

Compare

K+ Ca2+

Na+ Mg2+

Zn2+Fe2+Mn2+

chargeradius

ratio

1.03.0

1.70.82.7 2.72.5

4.7

higher ratiomeans more polarizing

Fe3+

4

Compare

K+ Ca2+

Na+ Mg2+

chargeradius

ratio

1.03.0

1.70.8

outside

inside

Na+

Na+

150 mM

18 mMmaintainpotentials,osmotic pressure

K+

K+

135 mM

3 mMCl-

Cl-

120 mM

7 mMmaintainpotentials,osmotic pressure

Ca2+

1.2 mM

Ca2+

0.0001 mM

exclude topreventtriggeringinside

Signaling by CaSignaling by Ca2+2+

1. increase in concentrationoutside

inside

Ca2+

1.2 mM

Ca2+

0.0001 mM

exclude topreventtriggeringinside

Signaling by CaSignaling by Ca2+2+

1. increase in concentration

2. binding to receptor protein

calmodulin

• very common protein

• binds Ca2+ very specifically (10,000 x Mg2+)

3. alters protein structure, triggers chemistry

5

Calmodulin structure

Lippard, S. J.; Berg, J. M. Principles of Bioinorganic ChemistryUniversity Science Books, Mill Valley, CA 1994, p 189, 191.

Signaling by CaSignaling by Ca2+2+

3. alters protein structure, triggers chemistry

• vision PDE 4200 turnovers per sec!

• Ca2+ pumps, muscle contraction

R-OH + ATP R-O-P-O-

O

Okinase

+ ADP + H+

Compare

K+ Ca2+

Na+ Mg2+

Zn2+Fe2+Mn2+

chargeradius

ratio

1.03.0

1.70.82.7 2.72.5

4.7

Fe3+5.9

blood coagulationwater treatment

Al3+

• Why a metal ion and not a molecule?

• Why a main group or a transition metal ion?

• Polarizing ability (charge density)

• Mn+ as Lewis acids (esp. Zn2+)

• Heme: common theme, tunable environment

• Redox: (e- but sometimes not H+ transfer)

• Transport, storage

6

Acid

Base

Brønsted-Lowry Lewis

e- pair acceptor

CO2(g)

e- pair donor

+ H2O(l) à H2CO3(aq)

H+ donor

H2CO3(aq)

H+ acceptor

+ H2O(l)à HCO3-(aq) + H3O+(aq)

demo: CO2 + water

Metals as Lewis AcidsMetals as Lewis Acids

Acid

Base(ligand)

O=C=O

H H

O

δ+ δ-

δ+

δ-

Mn+

H H

Oδ+

δ-

Zn

OH

H

Zn

OH

Hydrolysis by ZnHydrolysis by Zn2+2+ CO2 + H2O à HCO3- + H+

demo: Zn2+ + water

50 milliontimes fasterwith enzyme

Fast Hydrolysis at very mild pH’s

CO2 + OH- W HCO3-

ROPO3-2 + H2O W ROH + HOPO3

-2

alkaline phosphatase

carbonic anhydrase

demo: Zn2+ + water

Zn

OH H+

catalyze base hydrolysis at pH 7.3

Hydrolysis by ZnHydrolysis by Zn2+2+

7

• Why a metal ion and not a molecule?

• Why a main group or a transition metal ion?

• Polarizing ability (charge density)

• Mn+ as Lewis acids (esp. Zn2+)

• Heme: common theme, tunable environment

• Redox: (e- but sometimes not H+ transfer)

• Transport, storage

Fe

HemeHeme in general, a common iron environmentin general, a common iron environment

Why is blood red?Fe Fe

Fe Fe

O2 O2

Fe2+

2.74.7

Fe3+

Hemoglobin and OHemoglobin and O22 bindingbinding

Fe

HemeHeme in general, a common iron environmentin general, a common iron environment

8

HemeHeme in general, a common iron environmentin general, a common iron environment

Fe

NHis

hemoglobinmyoglobin

Fe

NHis

H3C-SMet

cytochromesb & c

Fe3+ + e- à Fe2+

Fe

OTyr

Fe

SCys

peroxidasescatalases

H2O2 à ½O2 + H2O

cytochromeP450

R-H à R-OH

demo: H2O2 + yeast

• Why a metal ion and not a molecule?

• Why a main group or a transition metal ion?

• Polarizing ability (charge density)

• Mn+ as Lewis acids (esp. Zn2+)

• Heme: common theme, tunable environment

• Redox: (e- but sometimes not H+ transfer)

• Transport, storage

Open Open vsvs closed shellclosed shell

O2- O2-

O2-

O2- O2-

Al3+

O2-

Cr2O3 AlAlAl222OOO333

[Ne]Cr3+

[Ar]3d3

redox is possible

PorphyrinPorphyrin (and related ligands) common(and related ligands) common

Mg2+Mg2+

9

Redox (eRedox (e-- transfer) without metalstransfer) without metals

N

CONH2

H

R

N

CONH2

H

R

H

H+, 2e-

NAD+ + H+ + 2e- NADH

NAD+ + H+ + 2e- NADHniacin

FAD + 2H+ + 2e- FADHriboflavin

Redox (eRedox (e-- transfer) without metalstransfer) without metals

NAD+ + H+ + 2e- NADHniacin

FAD + 2H+ + 2e- FADHriboflavin

Cu2+ + e- Cu+

Fe3+ + e- Fe2+

Mn4+ + 2e- Mn2+

Redox (eRedox (e-- transfer) transfer) withwith metalsmetals

NitrogenNitrogen• Can we live withoutnitrogen?

• Where is it found in ourbodies?

• How do we get it?• Can we get nitrogen from

N2 molecules in our lungs? “Nitrogen fixation is as interesting a scientific problem as I have encountered in my lifetime. It has everything: complicated chemistry, enzymology, microbiology, molecular biology, and agriculture.”

R. Holm, 1998

“...more scientists are working to understand how nitrogenase converts dinitrogen to ammonia...than are involved in all efforts to fix nitrogen any other way.”C. &. E. News, 1998

“...if you get enough electrons from the metals into the bridging, end-on dinitrogen, it will break...”M. D. Fryzuk, 1998

N N

10

Nitrogen: We canNitrogen: We can’’t live without it. How to get it?t live without it. How to get it?

“...if you get enough electrons from the metals into the bridging, end-on dinitrogen, it will break...”M. D. Fryzuk, 1998

reaction

conditions

catalyst

N2 + 3H2à 2NH3 N2 + 6H+ + 6e-à 2NH3

400 oC, 200 atm 25 oC, 1 atm

promoted FeOx Fe/FeMo enzyme

NitrogenaseNitrogenase: where N: where N22 meets its end.meets its end.N2 + 6H+ + 6e-à 2NH3

Photosynthesis Photosynthesis PlastocyaninPlastocyanin (Pc)(Pc)

Cu2+ + e- Cu+

fast e- transfer by controlling environment

Cu2+ Cu+

Ene

rgy

CuPc

e-

IronIron--Sulfur ClustersSulfur Clusters

11

• Why a metal ion and not a molecule?

• Why a main group or a transition metal ion?

• Polarizing ability (charge density)

• Mn+ as Lewis acids (esp. Zn2+)

• Heme: common theme, tunable environment

• Redox: (e- but sometimes not H+ transfer)

• Transport, storage

Metal (Transport) ChaperonesMetal (Transport) Chaperonesint

estin

e

blood

vese

l

pH = 7.3 Demo: Fe+3(aq) and base

Fe3+Fe3+(aq)

Fe(OH)3(s) at pH 7.3

Metal (Transport) ChaperonesMetal (Transport) Chaperones

intes

tine

blood

vese

l

pH = 7.3 Demo: Fe+3(aq) and base

Tf[Fe]

transferrin (Tf)

Tfbind Fe2+

hold/transportTf[FeIII]

releaseTf[FeII]

Storage, combat toxicityStorage, combat toxicity

Hg S

(sulfur rich proteins)metallothioneins

Pb