breitbach sem

8/3/2019 Breitbach Sem

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Chemical Approaches

to the Detection of ExplosivesAnthony S. Breitbach

Under the supervision ofHelen E. Blackwell, PhD

February 12, 2009


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Outline

2

Explosives

Explosive Detection

Colorimetric Tests

Amplifying Fluorescent Polymers

Enzymatic-Facilitated Chemical Sensors


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Explosives are Classified by Performance

Singh, S.J. Hazard. Mater. 2007, 144, (1-2), 15-28.3

ExplosivesEnergetic material that can undergo a very rapid

combustion releasing large amounts of energy .

Low

Subsonic Combustion

High

Supersonic Combustion

Pyrotechnics Propellants Primary Secondary

Initiators Main charge

Pb(N3)2

TNT


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Why are Compounds Explosive?

4

Exothermic combustion

Release large amounts of energy and gas

Internal oxidant

N-oxides (NO, NO2, NO3) as source of O

Nitromethane (NM)cH [kJ/mol] -709.2

Combustion velocity [km/s] 6.49

MethanecH [kJ/mol] -890.8

Combustion velocity [km/s] 1.4-1.64

Akhavan, J. Kirk-Othmer Encycl. Chem Technol., 5th ed.; Wiley: New York, 2005; Vol. 10, pp 719-744.


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Nitro Groups Easily Incorporated By Nitration

5

N-nitration

Aryl-nitration

O-nitration

Nitramines

Nitroaromatics

Nitrate Esters

Nitration via electrophilic substitution with nitronium ion

Olah, G. A. Nitration Methods and Mechanisms; VCH Publishers: New York, 1989.


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The Usual Suspects

6

Nitro

Aliphatics

Acid Salts

Nitro

AromaticsNitrate Esters

Peroxides

Nitramines

2,4,6-trinitroluene (TNT)

DV 7.07km/s

Nitromethane (NM)

DV 6.49 km/s

Ammonium Nitrate

Triacetone triperoxide (TATP)

DV 5.2 km/s

Hexamethylene triperoxide diamine (HMTD)

DV 4.5 km/s

Nitroglycerine(NG)

DV 8.08 km/s

Trinitro-triazacylohextane (RDX)

DV 8.63 km/s

Keshavarz, M. H.J. Hazard. Mater. 2007, 141, (3), 536-539.


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Detection Needed for Safety

7

Airports reduced number

of scheduled flights by

30% to allow increase

time for security checks

120 million

unexploded landmines

in 62 countries

unaccounted for

Kill or injure 30,000

people each year

TNT classed as toxic at >2ng/mL

Forensics

Homeland Security Global de-mining

Environmental Detection and Remediation

Singh, S.J. Hazard. Mater. 2007, 144, (1-2), 15-28.


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Canines Are Unreliable and Costly

8

PROS: Display high selectivity and sensitivity (up to 500ppt)

CONS: Unreliable, high cost and maintenance

High demand for new approaches to explosive detection

Habib, M. K. Biosens. Bioelectron. 2007, 23, (1), 1-18.


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Chemosensors Lead the Way

9

Dilemma types of radiation that yield

specific info about molecules and bonds

cannot penetrate objects

Trace

Detectors

Explosives

Detectors

Bulk

Detectors

Mass

SensorsBiosensorsChemosensors

Singh, S.J. Hazard. Mater. 2007, 144, (1-2), 15-28. Yinon, J.Anal. Chem. 2003, 75, (5), 98A-105A.


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Difficulties for Detection

10

Low vapor pressure

Vapor pressure depression

Mixtures

Binders

Packaging

Thermal vaporization causes degradation

Lack characteristic absorption bands

Increased usage of non-conventional explosives

Explosive

Vapor Pressure

[ppt (v/v)]

Chloroform 500,000,000

EGDN 100,000,000

NG 580,000

DNT 56,000

TNT 9,500

PETN 18

RDX 6

Increasing Difficulty for Detection

Kolla, P.Angew. Chem. Int. Ed. 1997, 36, (8), 800-811.


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Indirect Colorimetric Detection

12

Indirect detection using color reactions

Commercial kits available

PROS: simple, fast (30s), portable, disposable, versatile (>30 explosives), LOD 25-500ng

CONS: selectivity (false positives), poor sensitivity (requires large sample size)

Field Forensics, Inc.: ELITE Explosive Detector. http://www.fieldforensics.com/ (accessed Feb 2009)


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Nitroaromatics detected by reacting with nucleophiles to form colored JM complex.

Jackson-Meisenheimer (JM) Complex

13

-OH -OH

2,4,6-trinitrotoluene (TNT) 2,6-dinitrotoluene (DNT)

C3 JM Complex C1 JM ComplexTNT

Chen, H.; et. al.J. Am. Soc. Mass. Spectrom. 2004, 15, (7) 998-1004.


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Nitrite Assayed with Griess Test

14

Nitrite reduced to nitrosonium ion by treatment with reductant

Nitrate esters and nitramines undergo alkaline hydrolysis to release nitrite

RDX

Jenkins, T. F.; et. al. Talanta 1992, 39, (4), 419-428.


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Nitosonium Reacts to Colored Azo

15

RDX

CON: Interference with

other nitrites is an issue

Sulfanilic Acid Diazonium ion

1-naphthylamine

Colored Azo

Jenkins, T. F.; et. al. Talanta 1992, 39, (4), 419-428.


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Multiple Explosives Detection

16

Color reactions can be built into arrays and coupled with pattern detection

to build a nano-nose which mimics the olfactory sensing of dogs.

Color Reagents

Optical Fiber

Pattern Response

to Explosives

Yinon, J.Anal. Chem. 2003, 75, (5), 98A-105A.


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Fluorescent Quenching for Detection

17

Exploits electron accepting capability of nitro-containing explosives

HOMO

LUMO

HOMO

LUMO

LUMO

ERed: NB (-1.15V) < DNT (-0.9V) < TNT (-0.7V)Increased Reduction Potential =

Increased Quenching

Toal, S. J.; et. al.J. Mater. Chem 2006, 16, (28), 2871-2883.


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Amplified Fluorescent Quenching

18

Analyte

Analyte

Excited Fluorophores Quenched Fluorophore

Excited Fluorescent Polymer Amplified Quenched Polymer

Yinon, J.Anal. Chem. 2003, 75, (5), 98A-105A.


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Conjugated Fluorescent Polymers

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Polyacetylenes Poly(p-phenylene-

vinylenes)Poly(p-phenylene-

ethynylenes)

Polymeric

Porphyrins

Polysilanes Polymetalloles

Toal, S. J.; et. al.J. Mater. Chem 2006, 16, (28), 2871-2883.


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Polymetalloles Have Unique Electronics

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Metallacyclopenta-2,4-diene moiety

Highly fluorescent

Highly quenchable

Tunable electronics

2,5-diphenylsilol from ab initio calculations at the HF/6-31G* level

HOMO LUMO

*

*

Toal, S. J.; et. al.J. Mater. Chem 2006, 16, (28), 2871-2883. Sohn, H.; et. al.JACS 2003, 125, (13), 3821-3830.


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+TNT

29Si NMR Polymetallole

Downfield

Shift

Polymetalloles Form Selective Helix

21

Crystal structures and

models show polymetallolesform selective helices

29Si NMR studies indicate

weak Lewis Acid-Lewis Base

interaction

Sohn, H.; et. al.JACS 2003, 125, (13), 3821-3830. Sanchez, J. C.; et. al. Chem. Mater. 2007, 19, (26), 6459-6470.ppm


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Dehydrocoupling of Dihydrometallole

22

Poly(tetraphenylsilol)

[PSi]

Toal, S. J.; et. al.J. Mater. Chem 2006, 16, (28), 2871-2883. Sohn, H.; et. al.JACS 2003, 125, (13), 3821-3830.


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Quenching Efficiency Depends on Explosive

23

Quenching

Efficiency [M-1]

TNT DNT NB

4340 2420 1200

Quenching efficiency directly related to reduction potential:

TNT (-0.7V) > DNT (-0.9V) > NB (-1.15V)

Relative

Fluorescence

Quenching

Concentration of Explosive [M]


[PSi]

TNT

DNT NB

Sohn, H.; et. al.JACS 2003, 125, (13), 3821-3830.


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PROS: excellent sensitivity and selectivity, cheap, easily synthesized,

readily fielded for on-site use, and nontoxic

CONS: limited to nitroaromatics, interference from UV absorbers

PSi Detects Nitroaromatics

24

LOD [ng]DNT 50

TNT 30


[PSi]

Toal, S. J.; et. al.J. Forensic Sci. 2007, 52, (1), 79-83.


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PSiV More Delocalized and Stable

25

Metallole-vinylene polymers increased delocalization across the backbone and

is Si-C more thermally stable vs Si-Si bridge (> by 150 kJ/mol)

Si-vinylene easily incorporated with hydrosilylation.

Poly(tetraphenylsilol-vinylene)

[PSiV]

Sanchez, J. C.; et. al. Chem. Mater. 2007, 19, (26), 6459-6470.

60-70% Yield


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HOMO and LUMO Energies Calculated for Explosives and

Trimers PSiV and PSFV at the B3LYP/631G* Level of Theory

LUMO

HOMO

SOMO

4.6eV3.5eV

PSFV, Better Orbital Energy Matching

26

UV

Larger Band Gap = Higher Energy = Better Reduction Driving Force=

= Greater Sensitivity?

Poly(silafluorene-

vinylene) [PSFV]

Sohn, H.; et. al.JACS 2003, 125, (13), 3821-3830. Sanchez, J. C.; et. al. Chem. Mater. 2007, 19, (26), 6459-6470.


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PSiV and PSFV Have Increased Quenching

27

Quenching Efficiency [M-1]in Toluene

Polymer % Yield MW (GPC) n TNT DNT RDX

PSi 88 1500 4 4300 2400 x

PSiV 73 4000 10 10500 4300 x

PSFV 66 4300 21 10200 5500 x


[PSi]

Poly(tetraphenylsilol-vinylene)

[PSiV]

Poly(silafluorene-vinylene)

[PSFV]

Greater degree of polymerization

Greater quenching efficiency

Nitramine, RDX, not detected



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PSiV and PSFV More Accessible

28

Vinylene and silafluorene functionalities create more open helices than PSi

allowing greater access to Si centers.PSi PSiV PSFV



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PSFV More Ordered in Solid-State

29

PSFV red shifts in solid-state

Framework more ordered

Interchain - stacking

RelativeFluorescence

Intensity

Re

lativeFluorescence

Intensity

Solution

Solid

Solution

Solid

[PSiV] [PSFV]


No Change

RED Shift


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PSFV Detects RDX in Solid-State

30

Expl. PSiV PSFVPA 2 2

TNT 2 0.3

DNT 3 2

RDX X 2

HMX X 3PETN X 2

TNG X 3

PSFV detected nitramines and nitrate esters in solid-state

PSFV detected TNT from real-life contaminated samples

PSFV more susceptible to interferents (benzophenone 3 ng/cm2)

Solid-State LOD [ng cm-2]

Nitroaromatics

Nitramines

Nitrate Esters



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Fido, Worlds Most Sensitive

31

LOD in femto-gram

range (ppq)

Detection of vapor and

particulates

Used in Iraq

ICX Technologies: Amplifying Fluorescent Polymers Fido Detector. http://www.icxt.com (accessed Feb 2009)


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Peroxides a Challenge for Detection

32

Easily Synthesized

As powerful as TNTMore sensitive

Difficult to detect

Increased usage by terrorists

Schulte-Ladbeck, R.; et. al.Anal. Bioanal. Chem. 2006, 386, (3), 559-565.Dubnikova, F.; et. al.JACS 2005, 127, (4), 1146-1159.


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TATP Detected Indirectly with POD

33

TATP

2,2-azino-bis(3-ethylbenzothiazoline)-6-sulfonate (ABTS) Colored Radical Cation

H+

Schulte-Ladbeck, R.; et. al.Anal. Bioanal. Chem. 2006, 386, (3), 559-565.


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ABTS Oxidizes to Colored Cation

34Kadnikova, E. N.; et al.J. Mol. Catal. B: Enzym. 2002, 18, (1-3), 39-48.


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ACRO P.E.T.

35

Acid catalyzed decomposition

Horse-radish peroxidase

ABTS color detection

PRO: high selectivity, fast, cheap, disposable

CON: moderate sensitivity (mg), interference

TATP

Itzhaky, H.; Keinan, E. Method and Kit For the Detection of Explosives. U.S. Patent 6,767,717, 2004.ACRP Security Technologies: ACRO-P.E.T. www.acrosec.com/index.asp (accessed Feb 2009)


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Summary

36

Chemical approaches offer a more

reliable solution to explosive detection

Future Directions

More selective and sensitive color

reagents and fluorescent polymers

Incorporation of bio-selective elements

Arrays for Pattern Detection

Steinfeld, J. I.; et. al.Annu. Rev. Phys. Chem. 1998, 49, (1), 203-232. 48.

Yeah, but it doesnt

smell like a bomb


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Acknowledgements

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Special Thanks:

Prof. Helen Blackwell

Blackwell group

Practice talk attendeesDrew Palmer

Joey Stringer

Margie Mattmann

Reto Frei

Christie McInnis

Aaron Crapster

Teresa Beary

JP Gerdt

Melissa Mennig


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