"The many Wonders of FeEDTA: Room
Temperature Incineration of Pollutants, and
The Detection of Peroxide Based Explosives
Frank Cheng
Associate Professor of Chemistry
University of Idaho
Moscow, ID 83844-2343
Email: ifcheng@uidaho.edu
Tel.: 208-885-6387
Fax: 208-885-6173
Homepage:
http://www.chem.uidaho.edu/faculty/ifcheng/
10 September 2007
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1
Outline

Background and History of EDTA

I] Room Temperature and Pressure Combustion of
Organic Pollutants and Nerve Agent Surrogates –
The Search for a Green Oxidant

II] A Detector for Peroxide-Based Explosives

III] A Model for the Role of Calcium and Zinc in
Biological Oxidations
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EDTA – A brief history

Ethylenediaminetetraacetic acid

1930’s Ferdinand Munz first
synthesizes EDTA as a substitute
for amino acids in textile
processing.
COOH
N
COOH
COOH

Annual Production 100,000 metric
tons.
http://www.chm.bris.ac.uk/motm/edta/edtah.ht
m
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N
COOH
3
EDTA
CH2COOH
HOOCH2C
N
N
CH2COOH
HOOCH2C
•Finds widespread use in food, cosmetic and
pharmaceutical preparations
•Newer uses – manufacture of textiles and in paper-pulp
bleaching
Swedish pulping industry where the use of EDTA has increased from
2,000 metric tons to about 8,000 metric tons per year from 1990 to
2000.

Ekland, B; Bruno, E; Lithner, G.; Hans, B.; “Use of Etheylenediaminetetraacetic
acid in Pulp Mills and Effects on Metal Mobility and Primary Products”; Environ.
Toxicol. Chem.; 2002; 21(5), 1040-1051.
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EDTA – Modern Uses
http://en.wikipedia.org/wiki/EDTA






Industrial cleaning: complexation of Ca and Mg ions, binding of
heavy metals.
Detergents: complexation of Ca and Mg (reduction of water
hardness).
Pulp and paper industry: complexation of heavy metals during
chlorine-free bleaching, stabilization of hydrogen peroxide.
Textile industry: complexation of heavy metals, bleach stabilizer.
Food: added as preservative to prevent catalytic oxidation by
metal ions or stabilizer and for iron fortification.
Personal care: added to cosmetics to work in synergy with
preservatives and to improve product stability.
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EDTA – Modern Uses -http://en.wikipedia.org/wiki/EDTA






Oil production: added into the borehole to inhibit mineral
precipitation.
Dairy and beverage industry: cleaning of bottles from milk stains.
Flue gas cleaning: removal of NOx.
Medicine: used in chelation therapy (brand name Endrate®,
marketed by Hospira; generic product is also on the market) for
acute hypercalcemia and mercury and has been used for lead
poisoning.
Added to many soft drinks containing ascorbic acid and sodium
benzoate, to reduce the formation of benzene (a carcinogen).
Can be used in the recovery of used lead acid batteries.
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EDTA – Modern Uses http://www.dow.com/productsafety/images/edtachart.jpg
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EDTA – Modern Uses

Used in dentistry
as a root canal
irrigant to remove
compounds of
organic and
inorganic debris
(smearlayer).
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Metal Complexes http://en.wikipedia.org/wiki/EDTA

Agrochemicals: Fe, Zn and Cu
fertilizer, especially in calcareous
soils.

Photography: use of Fe(III)EDTA
as oxidizing agent.

Scavenging metal ions: in
biochemistry and molecular
biology, ion depletion is commonly
used to inactivate enzymes which
could damage DNA or proteins
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Complexation of Fe(II/III) with EDTA

pKa1-6 = 0.0, 1.5, 2.0, 2.66,
6.16, 10.24

Kf(FeII) = 1014.32

Kf(FeIII) = 1025.1
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Cyclic voltammetry - http://en.wikipedia.org/wiki/Cyclic_voltammetry
red
0.7 volts
ox

Applied potential waveform to electrode

ox + e- = red
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E0 = 0.7 volts
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The Cyclic Voltammogram
ox + e-  red
Start E
End E
ox + e- <-- red
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Cyclic Voltammetry of Fe(II/III)EDTA
8.00E-06

1.0 mM FeIIIEDTA
FeIIIEDTA + e-  FeIIEDTA
6.00E-06

pH 7.40, 0.1 M
HEPES buffer
10 mV/sec
4.00E-06
2.00E-06
Current (A)

0.00E+00
300
100
-100
-300
-500
-700
-2.00E-06

C disk electrode
-4.00E-06
FeIIIEDTA + e-  FeIIEDTA
-6.00E-06
Potential (mV)
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CV of Fe(II/III)EDTA in the presence of
O2

Electrocatalytic (EC’) Voltammetry
2
Figure 1. Cyclic
voltammetric curves on
a pH =3 sample
A
1.5
A) 0.1 mM FeIIIEDTA
and O2 saturated,
B) 0.1 mM FeIIIEDTA
only,
uA
1
0.5
B
B
0
-0.5 0.3
scan rate = 5 mV/s.
10 September 2007
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
V
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The reducing current is amplified and
oxidizing current is absent in EC’ mechanism

Electrochemical reduction coupled with a
homogeneous reaction

Fe EDTA  e 
 Fe EDTA
III
k'
II

2
Fe EDTA  O2  Fe EDTA  O
II
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k"
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III
15
Kinetic Realities
e-
FeIIIEDTA
fast
FeIIEDTA
Electrode
e-
O2
slow
O2.-
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Mediated Electron Transfer
Catalytic Current
Electrode
e-
FeIIIEDTA
O2
fast
FeIIEDTA
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fast
O2.-
17
The Fenton Reaction

FeIIIEDTA + e- = FeIIEDTA

FeIIEDTA + H2O2 = FeIIIEDTA + HO- + HO∙
(fast)

H2O2 + e- = HO- + HO∙ (slow)
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EC’ Voltammetry with the Fenton
Reaction Mechanism
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Summary of Voltammetry

EC’ mechanisms of

Fenton Reaction



FeIIIEDTA + e- = FeIIEDTA
FeIIEDTA + H2O2 = FeIIIEDTA + HO- + HO∙
Oxygen Reduction


FeIIIEDTA + e- = FeIIEDTA
FeIIEDTA + O2 = FeIIIEDTA + O2.-
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Outline of Investigation

I] Room Temperature and Pressure
Combustion of Organic Pollutants and Nerve
Agent Surrogates – The Search for a Green
Oxidant

II] A Detector for Peroxide-Based Explosives

III] A Model for the Role of Calcium and Zinc
in Biological Oxidations
10 September 2007
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The search for a “green” oxidant

Problems with chlorine based bleaching
methods.

Prefer low temperature and pressures,
energy savings

Oxygen is the ultimate green oxidant.

Oxygen is kinetically stable
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Overall Goals of Our Green Oxidation
Program
 The destruction or neutralization of xenobiotics,
including nerve agents and chlorinated pesticides
using green oxidation chemistry.
 Focus on non-biological oxygen activation to
eliminate the need for tricky enzyme based systems
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Molecular Oxygen

O2 is kinetically stable

Oxygen’s two unpaired
electrons make it difficult
to accept a bonding pair

Partially reduced oxygen
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Reactive Oxygen Forms
•O=O• b.o. = 2
 120 kcal/mol
+e-
•O-O• b.o. = 1.5
 80 kcal/mol
G
+4e+4H+
+2e+2H+
HO-OH b.o. = 1
 50 kcal/mol
2H2O
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Molecular Oxygen as a Facile Oxidant
superoxide
radical
+ e-
hydrogen
peroxide
•- + eO2
H2O2
hydroxyl
radical
+ e-
HO
+ e-
O2
H2O
- e-
- e-
•-
O2
H2O2
- e-
- e-
HO
•Diagram showing reaction oxygen intermediates between O2 and H2O.
•H+ left out for simplicity.
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The Fenton Reaction
H2O2 + e-  HO• + HOFe(II)  Fe(III) + eFe(II) + H2O2  Fe(III) + HO• + HO-
H.J.H. Fenton. J. Chem. Soc. 1894, 65, 889.
F. Haber and J.J. Weiss. Proc. Roy. Soc. London, Ser. A. 1934, 147, 332.
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Oxygen Activation

Biological

cytochrome P450
enzymes,
monooxygenase
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Fe°, EDTA, Air (ZEA) system
Fe(0),
EDTA, & air
The
only nonbiological system known to date that can
activate O2 under RTP and produce a facile oxidizing
species capable of extensively degrading xenobiotics
Organophosphorous
agents
Halocarbons
Organics
IF Cheng, et al, Ind. & Eng. Chem. Res. 2003, 42(21), 5024-5030.
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Zero-Valent Iron Remediation of
Halocarbons

Iron as a reducing agent for halogenated
organics

Fe(0) + R-X + H2O  Fe2+ + R-H + OH- + XCl x
Cl
CCl 3
Cly
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Cl
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Appearance of oxidation products

Fe(0) + R-X + H2O  Fe2+ + R-H + OH- + X-

Oxidized Hydrocarbons/LMW carboxylates
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Fe°, EDTA, Air (ZEA) system
III
Fe EDTA
Fe
0
O2
-
e
.-
.-
O2 + O2 + 2H+
II
Fe EDTA
2+
Fe + EDTA
II
Fe EDTA
10 September 2007
+
H2O2
III
-
Fe EDTA + HO
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+ HO·
32
Outline of ZEA Research

Introduction



General Reaction Scheme


Environmental Impact of EDTA
The RTP Dioxygen Activation
Zero-valent iron/EDTA/air (ZEA) system
Degradation Kinetics and Reaction Products

EDTA



Mechanisms


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Chlorinated phenols
Organophosphorus and UXO compounds
Rate-limiting Step
Conclusions
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Concerns about EDTA

Many industrial chelating agents are not degradable by methods
currently found in wastewater treatment facilities

Not readily biodegradable

Considerable quantities of EDTA pass through wastewater
treatment facilities in the form of FeIIIEDTA, as high as 18µM.
Sillanpaa, Mika; Orma, Marjatt; Ramo, Jaakko; Oikair; “The importance of ligand speciation in
environmental research: a case study”; The Science of the Total Environment; 2001; 267, 2331.
Sillanpaa, M; Pirkanniemi, K.; “Recent Developments in Chelate Degradation”; Environmental
Technology, 2001, 22, 791.
Kari, F. G.; Giger W; Modeling the Photochemical Degradation of Ethylenediaminetetraacetate in
the River Glatt; Environmental Science and Technology; 1995, 29, 2814.
Nirel, P. et. al.; Method for EDTA Speciation Deteremination: Application to Sewage Treatment
Plant Effluents; Wat. Res; 1998; 32, 3615.
Kari, F. G. and Giger W.; Speciation and fate of EDTA in municipal wasterwater treatment. Wat.
Res., 1996, 30, 122-134.
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Concerns about EDTA

Questions regarding the ability to mobilize
metals in the environment.




Currently not being monitored or treated at waste
water treatment facilities
Concern for heavy metal mobility and longer
bioavailability of metals to aquatic plants and animals
Stable in aquatic environment
EDTA is anthropogenic and long-lived.
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Goals
•The destruction or neutralization of EDTA (xenobiotics)
•Search for in situ conditions that will aid in the reduction
in the release of EDTA in emerging green chemistries.
Inexpensive & Safe Processes.
•Room Temperature and Pressure Conditions (RTP)
•Common Reagents – Long Term Storage
•No Specialized Catalysts
•System that may be incorporated into existing water
treatment systems
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Experimental Setup
1 mM EDTA (Total Vol. 50mL)
2.5g Fe° 30-40 mesh Aldrich
Open to the Atmosphere
125 ml round
bottom flask
Aliquots were taken directly from
reaction vessel, diluted, filtered and
injected into HPLC
stir bar
2.5 g Fe°
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Bioanalytical
Systems – RPM
controlled stir
plate
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Visual Detection of H2O2 Produced by
ZEA System

[HCl] = 0.04 M
[ammonium molybdate] = 0.08 mM
[KI] = 80 mM
[EDTA] = 0 or 1.2 mM
Agar (Starch)

Proposed




2FeIIEDTA + O2 + 2H+  2FeIIIEDTA + H2O2
H2O2 + 3I- +2H+  I3- + 2H2O
I3- + starch  blue-violet complex
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Iron wire: EDTA Absent & starch reagents
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Iron wire: EDTA Present
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EDTA required for the ZEA reaction
Qualitative Results
Fe(0) + O2 + 2H+  Fe2+ + H2O2
Slow
2FeIIEDTA + O2 + 2H+  2FeIIIEDTA + H2O2
Fast
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Evidence for Production of Reactive
Oxygen Species
I: Heterogeneous O2 Activation
O2
e-
Fe

ROS


O2.-
0
+ O2.- + 2H+
Fe2++ EDTA
FeIIEDTA
O2-•, H2O2, HO., FeIV=O, etc.
+
FeIIIEDTA
H2O 2
-
+ HO + HO
Two Analyses were performed


Thiobarbituric acid-reactive
substances (TBARS) assay
Addition of known radical
scavenger, 1-butanol
II: Homogeneous O2 Activation
FeIIIEDTA
Fe0
O2
eFeIIEDTA
O2.-
H 2O 2
FeIIIEDTA
+
O2.-
+
2H+
Fe2++ EDTA
FeIIEDTA
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+
-
+ HO +
HO
42
Suppression of EDTA degradation with the addition
of Radical Scavenger
1-butanol is a •OH radical scavenger
-6.5
(■) kobs = -1.11 M-1hr-1
ln [Fe III EDTA]
-7
-7.5
-8
Control (no Fe)
-8.5
EDTA, Air
-9
-9.5
5 mM 1-butanol
-10
Linear ( EDTA,
4 Air) 5
6
Linear (5 mM 1butanol)
0
1
2
3
Time (hrs)
(▲)kobs = -0.08 M-1hr-1
with 5mM 1-butanol
(2.5 g ZVI g, 1.00mM
EDTA, open to air)
Mantzavinos D; Water Res. 2004University
Jul;38(13):3110-8.
J Hazard
of Idaho - Washington
StateMater. 2004 Apr 30;108(1-2):95-102.
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Summary of ZEA system and O2



Both TBARS and butanol tests indicate that
ZEA system is able to produce facile oxidant
from air at RTP
Rare form of abiotic O2 activation at RTP
Identity of oxidant isn’t clear


HO·
FeIV=O
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Degradation of EDTA by ZEA reaction
COOH
HN
COOH
HOOC
N
HOOC
COOH
N
COOH
1 mM EDTA
(50mL, aqueous)
2.5g Fe° + air
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COOH
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HOOC COOH
CO2/HCO3-
45
Carbon Balance - Total Organic Carbon*, ESI-MS**, HPLC#
Table 1 : Carbon Balance 1mM EDTA, 2.5g ZVI, air, reaction volume 50mL, 6hrs
%C
CO2
35% (± 5)*
Iminodiacetic Acid
28% (± 3)**
Oxalic acid
17% (± 2)**
Propionic Acid
14 % (± 2)**
EDTA
2% (± 2)#
Total
96%
Trapping of the volatile gases using Tenax® showed no volatile organic carbon of molecular weight C4 and above
released from the system during the course of the reaction
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Products of ZEA System

None of the products of EDTA are significant metal
chelation agents.

All are more easily biodegraded.

The ZEA system has proven successful at the
degradation of other organic xenobiotics.



10 September 2007
Halocarbons
Organophosphorus
Organics
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Organophosphorous Nerve Agents and Nitrated
Explosive Surrogates
TNT surrogate, nitrobenzene (985 ppm) was decomposed in 24 hours.
VX surrogate, malathion (49 ppm) was consumed in 4 hours, to give
diethyl succinate. Malathion was the only pollutant to give a byproduct detectable by GC-FID.
H3C
O
CH3
O
+
+
H3C
O
O
H3C
H3C
CH3
N
N
O
O
O-
O-
-O
+
O
N
CH3
O
P
N
CH3
+
S
S
N
S
O
-O
VX
O
P
CH3
TNT
O
H3C
O
CH3
nitrobenzene
malathion
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Malathion Degradation
DES
H3C
malathion
O
O
H3C
H3C
O
CH3
O
O
max: 4-6 hrs
O
O
O
CH3
S
O
S
P
O
O
H3C
O
CH3
CH3
S
O
P
O
O
H3C
O
O
PO43- + SO42H3C
SO42-
:0.0593mM (14% yield) (24hrs)
PO42-
: 0.0825 mM (19 % yield) (24hrs)
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malaoxon
Max: 7 hrs
49
Kinetics of Malathion Degradation
Malathion
Diethyl Succinate (DES)
GC/FID chromatograph: each data point indicates an individual reaction vial
extracted using 50/50 hexane/ethyl acetate, error bars indicate the standard deviation
between three measurements of each sample vial.
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Kinetically stable organic products from ZEA
degradation.
iminodiacetic acid
(degrades after
12 hrs)
propionic acid
Degradation products for
10 September 2007
bicarbonate
succinic acid
Oxalic
acid
-EDTA
-Malathion
-4-chlorophenol
-pentachlorophenol
-phenol
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Overall Scheme (simplified)
This study
Beenackers
Ing. Eng. Chem.
Res. 1992, 32,
2580
Van Eldik
Inorg. Chem, 1997,
36, 4115-4120
25.5
kJ/mol
27.2
kJ/mol
33.9
kJ/mol
Metal dissolution:

Fe(0)  Fe2+ + 2e-
(1)
Complex formation

Fe2+ + EDTA  FeIIEDTA
(2)
Homogeneous O2 activation:

2FeIIEDTA + O2 + 2H+  2FeIIIEDTA + H2O2 (3)
Fenton Reaction

FeIIEDTA + H2O2  FeIIIEDTA + OH• + OH- (4)
EDTA degradation:

OH• + FeEDTA Fe2+/3+ + EDTA*
(5)

EDTA* = damaged EDTA
Redox Cycling:

FeIIIEDTA + e- FeIIEDTA
(6)
•Step 3 is Rate-Limiting
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Voltammetric Studies




ZEA reaction rate is dependent on pH
2.5 < pH < 4.5
LMW Acids Self Buffers the ZEA reaction at
3.5
Oxygen Activation Rates Measured By Cyclic
Voltammetry
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CV of Fe(II/III)EDTA in the presence of
O2

Electrocatalytic (EC’) Voltammetry
2
Figure 1. Cyclic
voltammetric curves on
a pH =3 sample
A
1.5
A) 0.1 mM FeIIIEDTA
and O2 saturated,
B) 0.1 mM FeIIIEDTA
only,
uA
1
0.5
B
B
0
-0.5 0.3
scan rate = 5 mV/s.
10 September 2007
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
V
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Electrocatalytic currents at -200mV at
5mV/s.
Current vs pH
Current(uA)
1.2000
1.0000
0.8000
0.6000
0.4000
0.2000
0.0000
0
2
4
6
8
10
12
pH
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2.5 < pH < 4.5
Current vs pH
Current(uA)
1.2000
1.0000
0.8000
0.6000
0.4000
0.2000
0.0000
0
2
4
6
8
10
12
pH
molar fraction
b
Free Fe2+
1.00
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00
FeIIEDTA
FeII(OH)2EDTA
FeII(OH)EDTA
FeIIH
0
FeIIHEDTA
(MLH)
2EDTA
2
4
6
8
10
12
14
pH
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Fe(II)HEDTA or MLH is responsible for
oxygen activation
N
N
N Fe
N Fe
I
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II
COOH
N
N Fe
COOH HOOC
O2
COOH
N
HOOC
N
COOH
III
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ZEA Reaction - Conclusions

This system is a viable option for the destruction of a variety of pollutants
and has a strong possibility for scale up.

The only system known to date that can obtain non-biological Oxygen
Activation at room temperature and pressure to produce reactive oxygen
species that are capable of fully degrading pollutants to LMW carboxylates
and inorganic forms

Due to the duality of EDTA acting as both a pro-oxidant and antioxidant,
controlling the [EDTA] is imperative to the success of the process.

Rate-limiting steps is (are) oxygen activation

FeIIEDTA may provide insights into biological oxygen activation
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Detector for Triacetone Triperoxide

Wikipedia http://en.wikipedia.org/wiki/Acetone_peroxide

Acetone peroxide (triacetone triperoxide, peroxyacetone,
TATP, TCAP) is an organic peroxide and a primary high
explosive.
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TATP Detector Outline

Background



Need for Detection Systems




Dangers
Recent News
Fast
Field Portable (handheld)
Selective and LOD
Electrochemical Detection Via Fenton Rxn
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TATP – the threat
• Due to the cost and ease
with which the precursors
can be obtained, acetone
peroxide is commonly
manufactured by those without the
resources needed to manufacture
or buy more sophisticated
explosives. When the reaction is
carried out without proper
equipment the risk of an accident
is significant.
•
http://en.wikipedia.org/wiki/Acetone_peroxide
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TATP – Ease of Synthesis

3H2O2 + 3CH3COCH3= ((CH3)2COO)3 + 3H2O

Ice Bath
3% H2O2 (30% or more preferable)
Acetone (paint thinner)
H2SO4 (battery acid)



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TATP – physiochemical characteristics



Shock Sensitive
Heat Sensitive
High V.P. 7 Pa @ 300K*

66% weight loss within 2 weeks at room temperature**

No Possible Commercial or Military Applications

*Propellants, Explosives, Pyrotechnics 30 (2005)127
**J. Am. Chem. Soc. 2005, 127, 1146-1159

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TATP is suicide bombers' weapon of
choice

Times (London) July 15, 2005 By Philippe Naughton

Rediscovered in the West Bank (Israel) in the early
1980s and soon became an extremists' staple.

Suicide Bombers – “Mother of Satan”

But as the Palestinian bomb-makers will attest - 40
Palestinians are thought to have been killed making
or handling the explosive - it is highly unstable and
sensitive to heat and friction.
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TATP – Most Recent News

NY Times Sept. 5, 2007

FRANKFURT, Sept. 5 — The German police have arrested
three Islamic militants suspected of planning large-scale
terrorist attacks against several sites frequented by
Americans, including discos, bars, airports, and military
installations.

She said the suspects had amassed large amounts of
hydrogen peroxide, the main chemical used to manufacture
the explosives used in the suicide bombings in London in July
2005.
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TATP – London Subway Bombings

July 7, 2005
http://news.bbc.co.uk/nol/shared/spl/hi/pop_ups/05/uk_enl_1121567244/img/1.jpg
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TATP – Shoe Bomber

http://www.univie.ac.at/cga/art/shoe_bomb3.gif
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TATP – Domestic Terrorists

http://www.koco.com/news/
5058347/detail.html

Sources Identify TATP As
Component Of Bomb
TATP Same Component Used By
Infamous Shoe Bomber
POSTED: 9:56 pm CDT October 4, 2005
UPDATED: 10:11 pm CDT October 4, 2005

NORMAN, Okla. -Sources confirmed
Tuesday night that at least
one of the components in
the bomb used by Joel
Henry Hinrichs III Saturday
night was a product called
TATP.
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TATP – TSA Fluid Ban

Effective November 10, 2006,
the TSA has advised that
travelers may now carry
through security checkpoints
travel-size toiletries (3.4
ounces/100 ml or less) that fit
comfortably in ONE, QUARTSIZE, clear plastic re-sealable
bag.



The 3-1-1 Kit contains six 2-1/2
oz and four 1-1/2 oz flexible
squeeze tubes, plus one 1-3/4
oz Envirosprayer.
Kit is also compliant with the
new International Security
Measures Accord.
http://www.easytravelerinc.com/
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TATP Detection the Challenge

The Need for a Fast Portable Detector

Innocuous Appearing White Powder

Despite a high VP Cannot be Sensed by
Dogs

Lacks Chromophoric Groups (not detectable
by UV-vis absorbance)
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TATP – Detector Requirements

Unknown Materials – Public Safety, e.g. Airports


Air Samples, e.g. Airports


Moderate Selectivity– Low Limits of Detection Required
Debris at Post-Explosion Sites


High Selectivity – Low Limits of Detection not Required
High Selectivity– Low Detection Limits
Field Portability
Schulte-Ladbeck, R.; Vogel, M.; Karst, U
Recent methods for the determination of peroxide-based explosives
Anal. Bioanal. Chem. 386 559-565 (2006)
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TATP - Detector

IR-Raman


Fluorescence/UV-vis Absorbance


Low LOD requires tagging
Ion Mobility


High Selectivity – Relatively High LOD
Good Selectivity, moderate LOD
HPLC or GC

Excellent Selectivity and LOD
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TATP – State of Detectors

Costs

Lack of Field Portability


Ideal – Handheld Sensor
May Require Knowledgeable User

e.g. Commercial Glucose Sensors
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Glucose Sensors - www.edaq.com/teachapp3.html
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DC Harris, Quantitative
Chemical Analysis 6th ed.
Chapter 17
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TATP – Detection by Electrochemical
Means


Proposed Basis For Detection
Fenton Reaction for Organic Peroxides
RO-OR + FeIIEDTA  RO- + RO· + FeIIIEDTA
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TATP – Electrochemical Detection
Reaction with Organic Peroxides is not Spontaneous
RO-OR + FeIIEDTA  N.R.
RO-OR + e-  RO- + RO·
FeIIEDTA  FeIIIEDTA + eEcell = Ecath – Eanod
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E0
<-0.5 V
0.1 V
-0.6 V
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TATP – Electrochemical Detection
Reaction with Peroxides and Hydroperoxides is
Spontaneous
RO-OH + e-  RO- + HO·
HO-OH + e-  HO- + HO·
E0
≈0.4 V
0.8 V
FeIIEDTA + RO-OH/HO-OH
FeIIIEDTA + RO∙/HO∙/H+

Requires that TATP be degraded
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TATP – Degradation to HOOH/ROOH

Acid degradation

TATP + H+  H2O2 + Products

0.250 M [HCl]
10 minutes

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TATP – Cyclic Voltammograms after Acid
Digestion
0.07
A
0.06
Current (mA)
0.05
0.04
0.03
0.02
0.01
B
0
-0.01
100
0
-100
-200
-300
-400
-500
Potential (mV)
Figure 1. Cyclic voltammograms of two solutions both containing 10 mM TATP
and 1 mM FeIIIEDTA under dearated conditions, 30 mV/s. A) Acid treated TATP.
B) Non-acid treated TATP.
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TATP – Chronoamperometric Detection


Simpler and Faster than Cyclic Voltammetry
Basis of the Glucose Sensor
E
E  E0 
0
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0.0592
[red ]
log
n
[ox]
time
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TATP -
4
3
E
0.0592
[red ]
EE 
log
n
[ox]
2
0
1
1/ 2
nFAD C
i
 1 / 2t 1 / 2
b
0
time
4
3
i
2

1
0
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0.025
0.023
Current (mA)
0.021
0.019
0.017
A
0.015
B
0.013
0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
Time (s)
Figure 3. Current-time measurements of a glassy carbon transducer in 1
mM FeIIIEDTA. A) 0.04 mM acid treated TATP, B) Background with
no TATP.
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0.04
0.035
y = 0.025x + 4E-05
R2 = 0.9999
Current (mA)
0.03
0.025
0.02
0.015
0.01
0.005
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
[TATP] mM
Figure 4. TATP calibration curve. The slope provides a sensitivity of 0.025
mA/mM TATP. The detection limit was found to be 0.886 μM. Error bars
indicate one standard deviation.
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Conclusions – Chronoamperometric
TATP Detection

0.886 µM LOD

O2 interference



FeIIEDTA + O2  FeIIIEDTA + O2.FeIIEDTA + HO-OH FeIIIEDTA + HO∙ + HO-
Requires Acid Pretreatment

10 min. Sample Pretreatment
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Future Work

Elimination of O2 interference




Metal Complex Reduction Potential
Kinetics of H2O2 vs. O2 reduction
Optimal Hydrolysis
Design of probes


Air Samples
Liquid Sample
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Acknowledgements
Derek Laine
Funding
NIH
Kenichi Shimizu
NSF
Simon McAllister
NSF-SGER
Ruhba Ponraj
Mark D. Engelmann, Ph.D. 2003
Tina Noradoun, Ph.D. 2005
Ryan Hutcheson, B.S. 2004
Rob Bobier, B.S. 2002
NASA
EPRI
BLM
UI
Terry Hiatt, B.S. 2000
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Reactive Oxygen Species (ROS) in Biology
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ROS and Inflammation
Phagocytes
Infections
-viruses
-bacteria
-parasites
Foreign Substances
-smoke
-asbestos
Damaged Tissue
-heat
-mechanical
-UV
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Activation of
Inflammatory
Cells
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ROS
RNS
90
ROS and Inflammation
ClO2.H2O2
NO.
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HOCl
+ Ca2+
ONOO.-
91
Iron Enzymes and the Fenton
Reaction
Hemes/Cytochromes
Oxygenases
Oxidases
H2O2
+ reducing agent
HO.
•All Fe-containing enzymes are quite good Fenton Reaction
agents.
•Oxidative Stress
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Inflammation
The Good
Inflammation protects the body
•Destroys invading pathogens
•Dissolves damaged tissue
The Bad
Chronic or prolong inflammation
Allergies and Autoimmune Diseases
•All the many types of allergies
•Many of the autoimmune diseases
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Role of Calcium in Inflammation
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Role of Calcium in Inflammation

Enhances Oxidative
Processes in
Inflammation
ROS


Paradoxically Redox
Inactive, i.e. always Ca2+
Inflammation
{
H2O2
O2.-
Ca2+
Role in Biological
Oxidations Not Well
Understood
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Inflammation Sequence
FeII
apoenzyme
HO·
ROS
Inflammation
{
H2O2
Cl-
HOCl
FeIIenzyme
O2.-
NO
ONOOCa2+
?
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The Low MW Iron Pool
FeII
apoenzyme
HO·
ROS
Inflammation
{
H2O2
Cl-
HOCl
FeIIenzyme
O2.NO
ONOO-
Ca2+
?
Fe
Fe released
into LMW pool
ROS
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Ligands for the LMW Fe pool






Glutamate
Citrate
Phosphates, e.g. ATP, ADP, GTP, etc.
Amino Acids
Peptides
Proteins (HMW)
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Fe(II/III)EDTA as a model for
physiological LMW Fe
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The concentration ratio of
[Chelate/Ligand]:[Fe] is very high



Physiological Concentration Mobile (Free)
Iron ≈ 10-9 M
[Chelates/Ligand] ≈ 10-3 M
Does this have any effect of the
reactivity of LMW-Fe in the Fenton Rxn?
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FeII/IIIEDTA CV in [Fe]:[EDTA] at 1:10
and 1:1
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EC’ CV of FeII/IIIEDTA (1:1) with H2O2



FeIIIEDTA + e- = FeIIEDTA
FeIIEDTA + H2O2 = FeIIIEDTA + HO- + HO∙ (fast)
H2O2 + e- = HO- + HO∙ (slow)
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EC’ current measured at -700 mV various
ratios of [Fe]:[Ligand]
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Excess molar EDTA and other Chelates
suppress Fenton Rxn kinetics
 = 102-104

FeII-OOH(EDTA)
(see references below)

FeII-OOH(EDTA) + Excess EDTA  FeII(EDTA) + HOOH

V. Zang, R. van Eldik “Kinetics and Mechanism of the Autoxidation of Iron(II) Induced through Chelation by Ethylenediaminetetracetate
and Related Ligands” Inorganic Chemistry 1990, 29, 1705-1711.

Ariane Brausam, Rudi van Eldik “Further Mechanistic Information on the Reaction Bewteen FeIIIEDTA and Hydrogen Peroxide:
Observations of a Second Reaction Step and Importance of pH” Inorganic Chemistry, 2004, 43, 5351-5359.

[1] Walling, C., Kurz, M., Schugar, H.J. 1970 “The Iron(III)-Ethylenediaminetetraacetic Acid-Peroxide System” Inorganic Chemistry, 9(4),
931-937
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Hypothesized Role of Calcium in
Inflammation
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Ca2+ increases Fenton Rxn Kinetics in
high [EDTA]:[Fe] ratios

Recovery of Fenton
reactivity of Fe complexes
by addition of Ca2+.

1:50 [FeIII]:[citrate]

1:20 [FeIII]:[NTA]
1:10 [FeIII]:[EDTA]


EDTA
Citrate
NTA
Other common conditions:
0.1 mM Fe3+, 22.8 mM
H2O2, and pH 7.4 HEPES,
carbon disk electrode, 10
mV/s sweep rate
0
0.3
0.5
0.7
1
2
5
10
Ca:L ratio
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Table 1: Stability Constants for M:L
complexes
Log β1 Ca+2
Fe+2
Fe+3
Ethylenediaminetetraacetic Acid (EDTA)
(HOOCCH2)2NCH2CH2N(CH2COOH)2
10.65
14.32
25.1
Nitrilotriacetic Acid (NTA) (HOOCCH2)3N
6.3
8.9
15.9
Citric Acid
HOOCCH2CH(OH)(COOH)-CH2COOH
3.45
4.4
11.5
•Ca2+ uptakes excess metal binding capacity without displacing FeII or FeIII
•Optimizes FeIIEDTA to the 1:1 molar ratio form
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FeII
apoenzyme
HO·
ROS
Inflammation
{
H2O2
Cl-
HOCl
FeIIenzyme
O2.NO
ONOO-
Ca2+
High [L]:[FeII]
Oxidatively inactive
Fe released
into LMW pool
Ca2+
optimized [L]:[FeII]
Oxidatively active
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FeII
apoenzyme
HO·
ROS
{
Inflammation
H2O2
Cl-
HOCl
FeIIenzyme
O2.-
Fe released
into LMW pool
NO
ONOOHigh [L]:[FeII]
inactive
Ca2+
redox cycling
H2O2
HO·
Damage to
DNA
Lipids
Proteins
optimized [L]:[FeII]
active
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Conclusions II

FeII/IIIEDTA is a good model for LMW
physiological iron

Ca2+ part of the inflammation cascade to
optimize Fe chelation sphere for the Fenton
Rxn.
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Other studies using FeEDTA

Sensor for Peroxide Based Explosives

O2 reduction catalysts for fuel cells
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Acknowledgements
Derek Laine
Funding
NIH
Kenichi Shimizu
NSF
Simon McAllister
NASA
Ruhba Ponraj
Mark D. Engelmann, Ph.D. 2003
Tina Noradoun, Ph.D. 2005
Ryan Hutcheson, B.S. 2004
EPRI
BLM
UI
Rob Bobier, B.S. 2002
Terry Hiatt, B.S. 2000
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http://www.moscow.com/
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www.latahrealty.com/
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Visit Our Web Site!
www.chem.uidaho.edu
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UI Stipend goes along way in Moscow,
Idaho
TA+Renfrew Scholarship 12 months
$18,800
Effective Fees
-$1,940
Health Insurance
-$1,200
Average One Bedroom Apt
$350-550
Average Two Bedroom Apt
$450-650
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