J. Am. Chem. Soc. 1998, 120, 12359-12360
12359
Complex, 1, was prepared by the literature procedure (eq 1).26a,d
Rapid Luminescent Detection of Phosphate Esters in
Solution and the Gas Phase Using
(dppe)Pt{S2C2(2-pyridyl)(CH2CH2OH)}
Kelly A. Van Houten, Danica C. Heath, and Robert S. Pilato*
UniVersity of Maryland
Department of Chemistry and Biochemistry
College Park, Maryland 20742
The chemical conversion of 1 to [(dppe)Pt{S2C2(CH2CH2-N-2-
pyridinium)}]+, 2, by activated phosphate esters (eq 2) can be
ReceiVed July 6, 1998
Organophosphate inhibitors of acetylcholine esterase (in-
cluding phosphinates and phosphonates) are used as pesticides
and as chemical warfare agents.1-7 As such, their detection over
a range of concentrations and conditions is required and has
attracted considerable attention.8-22 Several detection methods
rely on an immobilized acetylcholine esterase detector coupled
to a transducer (i.e., pH electrodes,5,9,11-13,15,16,22 fiber optics,10,21
and piezoelectric crystals14). Although the immobilized enzymes
are sensitive and detect a broad spectrum of acetylcholine esterase
inhibitors, they lack selectivity and are prone to false positives
when exposed to choline mimics.15,23,24
The rapid detection of volatile fluoro and cyano phosphates is
of particular interest since these are major constituents in the
chemical warfare arsenal. Reported is a new selective method
for the rapid detection of these esters. The method uses a new
platinum 1,2-enedithiolate complex with an appended alcohol that
upon exposure to selected phosphate esters is converted to a room-
temperature lumiphore.25
monitored by the emissions from 2 which have been assigned to
a thiolate to heterocycle π* intraligand charger-transfer singlet,
1ILCT*, and triplet, 3ILCT*. While 1, and 1H+, are nonemissive
(φ < 0.00001), 2 is emissive in room-temperature solution (1φ )
3
0.002, φ ) 0.01, DMSO) and when immobilized in cellulose
3
acetate/triethylcitrate films (1φ ≈ 0.01, φ ≈ 0.2).26
(1) Somani, S. M. Chemical Warfare Agents; Academic Press: San Diego,
1992.
Neutral pyridine-substituted complexes such as (dppe)Pt{S2C2-
(2-pyridyl)(R)} R ) H, and CH2CH2OH, are not emissive due to
a lowest lying d to d transition which leads to rapid nonradiative
decay of emissive excited states.26 However, the emissive
properties of 2 are similar to those of [(dppe)Pt{S2C2(2-pyridini-
um)(H)}]+ suggesting that either the steric bulk or solution
dynamics of the [(dppe)Pt{S2C2(2-pyridinium)(CH2CH2OH)}]+
side-chain increases the nonradiative decay rate. The gross
differences in the photophysical properties of 2 and [(dppe)Pt-
{S2C2(2-pyridinium)(H)}]+ from those of 1H+ could arise from
the necessity for the 1,2-enedithiolate and heterocycle to be
coplanar for emission from the ILCT excited states.26d Whereas
in 2 the 1,2-enedithiolate and heterocycle are held coplanar in
the ground state,26d the ability of the 1,2-enedithiolate and het-
erocycle to be coplanar in the [(dppe)Pt{S2C2(2-pyridinium)(R)}]+
complexes depends on the bulk of the R group, and this could
account for the emission from R ) H and not R ) CH2CH2OH.
Given the chemical reactivity of 1 and combined photophysical
properties of 1 and 2, activated phosphate esters serve to turn on
the emission in this family of complexes. The reaction of 1 with
phosphate, thiophosphate, and phosphinate esters (10-1-10-6 M)
leads to the generation of 2 (eq 2). These reactions can be
followed by exciting a deaerated CH2Cl2 solution at 450 nm and
monitoring the 605 and 710 nm emissions.
(2) Skladal, P. Food Technol. Biotechnol. 1996, 34, 43-9.
(3) Gunderson, C. H.; Lehmann, C. R.; Sidell, F. R.; Jabbari, B. Neurology
1992, 42, 946-50.
(4) Khan, S. U. Pesticides in the Soil EnVironment; Elsevier: Amsterdam,
The Netherlands, 1980.
(5) Hendji, A. M. N.; Jaffrezic-Renault, N.; Martelet, C.; Clechet, P. Anal.
Chim. Acta 1993, 281, 3-11.
(6) Ember, L. Chem. Eng. News 1993, 71, 1, 8-9.
(7) Quinn, D. M.; Balasubramanian, A. S.; Doctor, B. P.; Taylor, P. Enzymes
of the Cholinesterase Family; Plenum Press: New York, 1995.
(8) Paddle, B. M. Biosens. Bioelectron. 1996, 11, 1079-113.
(9) Tran-Minh, C.; Pandey, P. C.; Kumaran, S. Biosens. Bioelectron. 1990,
5, 461-71.
(10) Rogers, K. R.; Cao, C. J.; Valdes, J. J.; Elderfrawi, A. T.; Elderfrawi,
M. Fundam. Appl. Toxicol. 1991, 16, 810-20.
(11) Fernando, J. C.; Roger, K. R.; Anis, N. A.; Valdes, J. J.; Thosmpson,
R. G.; Eldefrawi, A. T.; Eldefrawi, M. E. J. Agric. Food Chem. 1993, 41,
511-6.
(12) Palleschi, G.; Bernabei, M.; Cremisini, C.; Mascini, M. Sens. Actuators,
B 1992, 7, 513-7.
(13) La Rosa, C.; Pariente, F.; Hernadex, L.; Lorenzo, E. Anal. Chim. Acta
1995, 308, 129-36.
(14) Negeh-Ngwainbi, J.; Foley, P. H.; Kuan, S. S.; Guibault, G. G. J.
Am. Chem. Soc. 1986, 108, 5444-7.
(15) Rogers, K. R.; Foley, M.; Altert, S.; Koga, P.; Eldefrawi, M. Anal.
Lett. 1991, 24, 191-8.
(16) Kumaran, S.; Morita, M. Talanta 1995, 42, 649-55.
(17) Lenz, D. E.; Brimfield, A. A.; Cook, L. A. In DeVelopment of
Immunoassays for Detection of Chemical Warfare Agents; Lenz, D. E.,
Brimfield, A. A., Cook, L. A., Eds.; American Chemical Society: Washington,
DC, 1997; Vol. 657, pp 77-86.
Sulfonyl chlorides and anhydrides convert 1 to 2 while car-
boxylic acid chlorides and anhydrides convert 1 to the corre-
sponding nonemissive esters. As such, these reagents interfere
with phosphate detection. However, amines and pyridines (com-
mon acetylcholine esterase inhibitors) have essentially no effect
upon this phosphate detection.
(18) Ewing, K. J.; Dagenais, D. M.; Bucholtz, F.; Aggarwal, I. D. Appl.
Spectrosc. 1996, 50, 614-8.
(19) Taranenko, N.; Alarie, J. P.; Stokes, D. L.; VoDinh, T. J. Raman.
Spectrosc. 1996, 27, 379-84.
(20) Polhujis, M.; Langenberg, J. P.; Benschop, H. P. Toxicol. Appl.
Pharmacol. 1997, 146, 156-161.
(21) Anis, N. A.; Wright, J.; Rogers, K. R.; Thompson, R. C.; Valdes, J.
J.; Eldefrawi, M. E. Anal. Lett. 1992, 25, 627-35.
(22) Marty, J. L.; Sode, K.; Karube, I. Electroanalysis 1992, 4, 249-52.
(23) Taylor, P. The Pharmacological Basis of Therapeutics, 7th ed.;
MacMillan Co.: New York, 1985.
(26) (a) Kaiwar, S. P.; Hsu, J. K.; Liable-Sands, L. M.; Rheingold, A. L.;
Pilato, R. S. Inorg. Chem. 1997, 36, 4234-40. (b) Kaiwar, S. P.; Vodacek,
A.; Blough, N. B.; Pilato, R. S. J. Am. Chem. Soc. 1997, 119, 9211-4. (c)
Kaiwar, S. P.; Vodacek, A.; Blough, N. V.; Pilato, R. S. J. Am. Chem. Soc.
1997, 119, 3311-6. (d) Van Houten, K. A.; Heath, D. C.; Barringer, C. A.;
Rheingold, A. L.; Pilato, R. S. Inorg. Chem. 1998, 37, 4647-53.
(24) O’Brien, R. D. Insecticides: Actions and Metabolism; Academic
Press: New York, 1967.
(25) Van Houten, K. A.; Heath, D. C.; Pilato, R. S., patent pending.
10.1021/ja982365d CCC: $15.00 © 1998 American Chemical Society
Published on Web 11/13/1998