Hydrolysis Kinetics of Thifensulfuron Methyl in Aqueous Buffer Solutions

Article abstract of DOI:10.1021/jf950194f

The hydrolysis of thifensulfuron methyl and thifensulfuron were investigated in buffered aqueous solutions with pH values of 4, 5, 9, and 10. Hydrolysis of thifensulfuron methyl was pH dependent and relatively fast both in acidic and alkaline buffer solutions. In the case of thifensulfuron, hydrolysis rates were of the same order of magnitude as thifensulfuron methyl at acidic pH, but very low at alkaline pH. In acidic solutions, cleavage of the sulfonylurea bridge and O-demethylation of the methoxy group of the triazine ring occurred concurrently. The resulting intermediates gave two parallel reactions: cleavage of the sulfonylurea bridge and opening of the triazine ring. The relative rates of the different hydrolysis pathways were influenced by the pK_aof compounds. At alkaline pH, thifensulfuron methyl hydrolyzed to thifensulfuron, which was slowly transformed by cleavage of the sulfonylurea bridge and O-demethylation.

Full text of DOI:10.1021/jf950194f

J. Agric. Food Chem. 1996, 44, 333
−337
333
Hyd r olysis Kin etics of Th ifen su lfu r on Meth yl in Aqu eou s Bu ffer
Solu tion s
J ean-Pierre Cambon* and J ean Bastide
Centre de Phytopharmacie URA CNRS 461, Universite´ de Perpignan, 52 Avenue de Villeneuve,
66860 Perpignan, France
The hydrolysis of thifensulfuron methyl and thifensulfuron were investigated in buffered aqueous
solutions with pH values of 4, 5, 9, and 10. Hydrolysis of thifensulfuron methyl was pH dependent
and relatively fast both in acidic and alkaline buffer solutions. In the case of thifensulfuron,
hydrolysis rates were of the same order of magnitude as thifensulfuron methyl at acidic pH, but
very low at alkaline pH. In acidic solutions, cleavage of the sulfonylurea bridge and O-demethylation
of the methoxy group of the triazine ring occurred concurrently. The resulting intermediates gave
two parallel reactions: cleavage of the sulfonylurea bridge and opening of the triazine ring. The
relative rates of the different hydrolysis pathways were influenced by the pKa of compounds. At
alkaline pH, thifensulfuron methyl hydrolyzed to thifensulfuron, which was slowly transformed by
cleavage of the sulfonylurea bridge and O-demethylation.
Keyw or d s: Sulfonylurea herbicide; hydrolysis; thifensulfuron methyl
INTRODUCTION
Methyl 3-[[[[(4-hydroxy-6-methyl-1,3,5-triazin-2yl)amino]-
carbonyl]amino]sulfonyl]-2-thiophene methyl carboxylate (4)
was prepared by mixing concentrated HCl (1 mL; d ) 1.19;
37%) and anhydrous tetrahydrofuran (50 mL) at room tem-
perature. After 2 min of stirring, thifensulfuron methyl (1, 1
g) was added and the mixture was allowed to stir for 2 h. The
white precipitate formed was collected by filtration and
recrystallized from ethanol to afford 350 mg of a white solid
of 4 (35% yield): mp 227-228 °C; IR (Nujol) υ (cm-1) 1784,
The sulfonylurea herbicides are subject to both chemi-
cal hydrolysis and microbial degradation in the soil
(Harvey et al., 1985; Beyer et al., 1988). Their degrada-
tion rates are related to sulfonylurea structures. All
sulfonylurea herbicides degrade relatively rapidly in
soil, but half-lives (t1/2) of ∼1-8 weeks, depending on
the specific compounds, have been reported (Brown,
1990). The slowly dissipating sulfonylurea herbicides
chlorsulfuron, metsulfuron methyl, and chlorimuron
were chemically hydrolyzed in acidic conditions by
cleavage of the sulfonylurea bridge and O-demethylation
of triazine ring (Sabadie, 1990, 1991, 1992; Reiser et
al., 1991). The more rapidly dissipating sulfonylurea
herbicides have shown different pathways of chemical
hydrolysis. The sulfonylurea bridge of tribenuron meth-
yl was easily broken in aqueous solutions (Brown, 1990),
whereas rimsulfuron rapidly hydrolyzed in both acidic
and alkaline conditions through contraction of the
sulfonylurea bridge (Schneiders et al., 1993).
Thifensulfuron methyl rapidly degraded in soil by a
microbial mechanism (t1/2 ) 2-3 days; Smith et al.,
1990; Cambon and Bastide, 1992) to give thifensulfuron.
In this paper, we report an investigation of the chemical
hydrolysis mechanism of thifensulfuron methyl and its
transformation products in aqueous buffer solutions (pH
4, 5, 9, and 10). The different reaction rate constants
and pathways of hydrolysis were determined.
1
1734, 1716; H NMR (DMSO-d6) δ 2.23 (s, 3H, CH3), 3.85 (s,
3H, CO2CH3), 7.6 (d, 1H, CH), 8.02 (d, 1H, CH), 11 (s, 1H,
OH), 12.85 (s, 1H, NH), 13 (s, 1 H, NH).
1-(Methylthiophene-2-carboxylate-3 sulfonyl)-7-acetyltriuret
(5) was prepared by adding concentrated HCl (0.5 mL) to a
solution of thifensulfuron methyl (0.5 g) in 80 mL of methanol.
The reaction mixture was stirred at room temperature for 3
days. The precipitate formed was filtered, and 5 was obtained
as a white solid (0.1 g): mp 205-206 °C; IR (Nujol) υ (cm-1
3272, 3175, 1733, 1723, 1698; H NMR (DMSO-d6) δ 2.20 (s,
3H, CH3), 3.9 (s, 3H, CO2CH3), 7.7 (d, 1H, CH), 8.12 (d,1H,
CH), 10.3 (s, 1H, NH), 11.08 (s, 1H, NH), 11.09 (s, 1H, NH).
)
1
3-(4-Hydroxy-6-methyl-1,3,5-triazin-2-ylcarbamoylsulfamoyl)-
thiophene-2-carboxylic acid) (7) was prepared by dissolving a
mixture of thifensulfuron (0.5 g) in anhydrous tetrahydrofuran
(50 mL) and concentrated HCl (1.5 mL) and stirring the
mixture at room temperature for 19 h. The precipitate was
filtered, and 7 was obtained as a white solid (72% yield): mp
1
285-294 °C; IR (Nujol) υ (cm-1) 3553, 1782, 1716; H NMR
(DMSO-d6) δ 2.19 (s, 3H, CH3), 7.76 (d, 1H, CH), 7.41 (d, 1 H,
CH), 10.4 (b, 1H, CO2H).
1-(Thiophene-2-carboxylic acid-3 sulfonyl)-7-acetyltriuret (8)
was prepared by dissolving a mixture of thifensulfuron (0.5
g) in anhydrous tetrahydrofuran (50 mL) and concentrated
HCl (2 mL) and stirring the mixture at room temperature for
6 days. The precipitate was filtered, and 8 was obtained as a
white solid (50% yield): mp >295 °C; IR (Nujol) υ (cm-1) 3334,
1714, 1694, 1682; 1H NMR (DMSO-d6) δ 2.1 (s, 3H, CH3), 7.58
(d, 1H, CH), 7.96 (d, 1H, CH).
MATERIALS AND METHODS
Ch em ica ls. Thifensulfuron methyl [methyl 3-[[[[(4-meth-
oxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]-
2-thiophene methyl carboxylate, 1] was a gift of Procida
(Marseille, France). Thifensulfuron 3-[[[[(4-methoxy-6-methyl-
1,3,5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]-2 thiophene
carboxylic acid; 2] was prepared according to the method of
Smith et al. (1990). Methyl 3-sulfamoylthiophene-2-carboxylate
(3) and 3-sulfamoylthiophene-2-carboxylic acid (6) were pre-
pared according to the method of Bastide et al. (1994).
Bu ffer Solu tion s. Five buffer solutions were used. Buffer
A (pH 4) consisted of 33 mL of citric acid solution (0.1 M) and
17 mL of Na2HPO4 solution (0.2 M) diluted to a total of 100
mL. Buffer B (pH 5) consisted of 24.3 mL of citric acid solution
(0.1 M) and 25.7 mL of Na2HPO4 solution (0.2 M) diluted to a
total of 100 mL. Buffer C (pH 7) consisted of 41.3 mL of KH2-
PO4 (1/15 M) and 58.7 mL of Na2HPO4‚2H2O (1/15 M). Buffer
D (pH 9) consisted of 50 mL of a mixture of both KCl (0.1 M)
* Author to whom correspondence should be ad-
dressed (fax 3368662223; e-mail BASTIDE@UNIV-
PERP. FR).
0021-8561/96/1444-0333$12.00/0
© 1996 American Chemical Society

334 J. Agric. Food Chem., Vol. 44, No. 1, 1996
Cambon and Bastide
Ta ble 1. Typ ica l HP LC Reten tion Tim es of
Th ifen su lfu r on Meth yl a n d Meta bolite Refer en ce
Sta n d a r d s
A, B, D, and E; 0.5 mL of 2 to buffers A and B; 0.4 mL of 2 to
buffers D and E; 2.9 mL 4 to buffers A and B; and 2.6 mL of
7 to buffers A, B, D, and E. The solutions were maintained
at 28 °C in the dark. Aliquots (0.5 mL) were aseptically
removed from each flask at appropriate times, depending on
the rate of hydrolysis. Each sample was analyzed by HPLC,
and each experiment was run in triplicate.
HPLC retention time (Rf), min
compd
method 1a
method 2b
4
3
5
1
6
7
8
2
4.61
6.41
7.26
10.93
3.94
3.20
-
17.40
14.32
64.43
-
An a lytica l Meth od s. Herbicide and metabolite concentra-
tions of aqueous samples were analyzed by a Laboratory Data
Control division of Milton Roy (Constametric I) high-perfor-
mance liquid chromatograph (HPLC) equipped with a Valco
injection valve, a UV detector (Monitor III), and a 250 × 4.6
mm Ultrabase 235, C8, 5 µm analytical column. The typical
HPLC retention times for thifensulfuron methyl and potential
transformation products are listed in Table 1. The detection
7.53
9.64
20.51
21.94
5.45
a
Method 1: the mobile phase consisted of water:acetonitrile:
limit of each compound was between 0.05 and 0.1 mg‚L-1
.
acetic acid, 60:40:0.6 (v/v/v); flow rate, 1 mL/min; UV detector, 254
b
nm. Method 2: 2, 6, 7, and 8 were analyzed with a mobile phase
of water:acetonitrile:trifluoroacetic acid (80:20:0.3, v/v/v); flow rate,
1 mL/min; UV detector, 254 nm.
RESULTS
Hyd r olysis P r od u cts. Products 2, 4, 5, 7, and 8
were synthesized according to standard procedure and
identified by IR, 1H NMR (see Materials and Methods),
and 13C NMR (Table 2). The structure of 5 was
confirmed by X-ray analysis (data not shown).
Hyd r olysis Ra te of Th ifen su lfu r on Meth yl a t p H
4 a n d 5. The hydrolysis rate of thifensulfuron methyl
is pH dependent and follows pseudo-first-order kinetics
(Table 3). This reaction shows two different pathways
(Figure 1): cleavage of the sulfonylurea bridge (path a)
to yield 3 and O-demethylation of the methoxy group
of the triazine ring (path b) giving 4. This latter
compound was transformed either into 3 by cleavage of
the sulfonylurea bridge (path c) or into 5 by opening of
the triazine ring (path d). The different hydrolysis
products were identified on the basis of their HPLC
retention times compared with authentic standards
and boric acid (0.1 M) and 20.8 mL of a NaOH (0.1 M) solution
diluted to a total of 100 mL. Buffer E (pH 10) consisted of 50
mL of both KCl (0.1 M) and boric acid (0.1 M) and 43.7 mL of
solution of NaOH (0.1 M) diluted to 100 mL.
Hyd r olysis Ra te Deter m in a tion . The hydrolysis rates
were determined by monitoring the rate of disappearance of
thifensulfuron methyl (1), thifensulfuron (2), and 4 and 7 in
aqueous buffers A, B, D, and E. All glass apparatus were heat-
sterilized by autoclaving, and buffer solutions were sterilized
by filtration (Sartorius Minisart NML, 0.22 µm). Aseptic
techniques were used throughout the study to maintain
sterility.
Two stock solutions containing 4 g‚L-1 of 1 or 2.1 g‚L-1 of 2
in acetonitrile were prepared. Compounds 4 and 7 are
unstable in acetonitrile, so the stock solutions were prepared
in 0.52 and 0.58 g‚L-1 of buffer C, respectively.
An aliquot of each stock solution was added aseptically to
50 mL of each sterilized buffer solution 0.375 mL of 1 to buffers
Ta ble 2. 13C NMR Ch em ica l Sh ifts in DMSO-d 6 13C Sp ectr a Recor d ed on a J EOL 400 MHz)
(
carbon
structure
group
1
2
3
4
5
6
7
8
9
10
11
12
A
R ) CH3
R′ ) CH3
R ) H
R′ ) CH3
R ) CH3
R′ ) H
R ) H
R′ ) H
R ) CH3
R ) H
133.1
141.4
132.1
133.1
148.5
163.8
163.9
163.3
163
170.1
178.4
159.3
53.12
55.22
25.07
A
A
A
135.9
134
140.8
141.1
141.1
131.6
131.9
131.8
131.1
131.7
131.1
149.2
149.2
150
170.1
170.9
170.1
178.5
153.2
153.4
160.6
159.9
160.6
55.17
25.18
21.07
21.36
53.33
53.27
135.5
B
B
133.3
113.5
141.3
140.7
132.1
131.4
131.6
131.3
148.1
148.2
149.5
149.7
173
173
150.3
150.2
159.4
160.4
23.95
24.01
Ta ble 3. F ir st-Or d er Ra te Con sta n ts of 1 a n d 4 a t p H 4, 5, 9, a n d 10
k × 102 h-1 a
compd 1
compd 4
pH
kobs
k1
k2
kobs
k3
k4
4
5
9
2.41 ( 0.02
0.25 ( 0.02
0.71 ( 0.15
11.55 ( 0.25
1.34 ( 0.06
0.13 ( 0.01
1.07 ( 0.08
0.12 ( 0.01
2.37 ( 0.19
0.40 ( 0.06
0.84 ( 0.06
0.22 ( 0.08
1.52 ( 0.13
0.18 ( 0.02
10
a
Data are means ( SD of three replicates.

Thifensulfuron Methyl Hydrolysis
J. Agric. Food Chem., Vol. 44, No. 1, 1996 335
was determined by studying the hydrolysis of 4 under
the same conditions. In this case
[3] ) [3](path a) + [3](path c)
[3](path c)
[5]
[3](path a)
k3
k4
k1
k2
)
and
)
[3](path c) + [5]
k3[5]
[3] -
k1
k2
k4
)
k3[5]
+ [5]
k4
F igu r e 1. Proposed acidic hydrolysis pathway of thifensul-
furon methyl (1) in aqueous buffer solutions (pH 4 and 5) at
28 °C (k represents reaction rate constants).
A ratio k1/k2 ) 1.33 was calculated from the latter
equation. The k2 value was 1.03 × 10-2 h-1
.
Method 3. Measurement of the Concentration of the
Different Products When 4 is Maximum. At the reaction
time when 4 is maximum
d[4]
dt
-
) 0
) k2 (a - x) - (k3 + k4)[4]
Here (a - x) is the concentration of the product 1 at t )
48 h, and k3 + k4 ) kobs (transformation rate of 4). The
k2 value calculated according to this method is 1.0 ×
10-2 h-1
.
The three different methods lead to similar k2 values
(k2 ≈ 1.0 × 10-2 h-1). The same hydrolysis pathways
were observed at pH 5, although the relative transfor-
mation rates were not affected to the same magnitude.
The different k values were calculated from the same
methods as for pH 4 and are reported in Table 3.
Hyd r olysis Ra te of Th ifen su lfu r on a t p H 4 a n d
5. Three transformation products were detected by
HPLC in these reactions and were identified as 6, 7,
and 8. In acidic aqueous solution, thifensulfuron (2) and
thifensulfuron methyl (1) hydrolysis pathways were
similar; that is cleavage of the sulfonylurea bridge (path
e) to yield 6 and conversion of the methoxy group on
the triazine ring to hydroxyl function (path f) to give 7.
Further hydrolysis of this latter compound leading to 6
(path g) and 8 (path h) was also observed (Figure 3).
The rate constants of the different hydrolysis reactions
were calculated by the method previously described for
the hydrolysis of 1 (Table 4).
F igu r e 2. Hydrolysis of thifensulfuron methyl (1) in pH 4
buffer solution at 28 °C.
(Table 1). The relative rates of these different reactions
can be estimated by three different methods.
Method 1. Measurement of the Initial Formation Rate
of 3 and 4. At the beginning of the reaction (pH 4), the
product 5 was present at very low concentration (Figure
2), which allows us to neglect this transformation. In
this condition, the ratio of the concentrations of 3 and
4 and the ratio of their rate constants are the same.
The hydrolysis rate of thifensulfuron is lower at pH
4 (Figure 4) and higher at pH 5 than the respective
thifensulfuron methyl hydrolysis rates. The relation
between pH and hydrolysis rates of chlorsulfuron and
metsulfuron methyl have been reported by Sabadie
(1990, 1991) and Dinelli et al. (1994). At pH > pKa,
a
linear relation between pH and log k, with a slope of
∼1 was obtained. At pH < pKa, the slope was <0.4.
The pKa of thifensulfuron methyl is 4, and the variations
in rate constants versus pH are in agreement with the
results reported for other sulfonylureas. The pKa of
thifensulfuron was measured as 4.6-4.7. This value
explains the low variation of rate constants observed
between pH 4 and 5.
The hydrolysis rates of the O-demethylated compound
7 were measured at pH 4 and 5, and the rate constants
calculated followed first-order kinetics (Table 4). The
hydrolysis of product 7 at pH 4 was faster than thifen-
sulfuron 2 hydrolysis, although at pH 5, the hydrolysis
k1
k2
[3]
[4]
)
and
kobs ) k1 + k2
These ratios give the values k1/k2 ) 1.24, k1 )1.34 ×
10-2 h-1, and k2 ) 1.07 × 10-2 h-1
.
Method 2. Analysis of Final Concentrations of Com-
pounds. When the hydrolysis reaction is completed, the
products 3 and 5 are relatively stable and their concen-
trations do not change. Compound 5 was obtained by
hydrolysis pathway d and 3 was formed by paths a and
c. The amount of 3 formed by path c was related to the
amount of 5 in solution by the ratio k3/k4. This ratio

336 J. Agric. Food Chem., Vol. 44, No. 1, 1996
Cambon and Bastide
Ta ble 4. F ir st-Or d er Ra te Con sta n ts of 2 a n d 7 a t p H 4, 5, 9, 10
k × 102 h-1 a
compd 2
k′1
compd 7
k′3
pH
k′obs
k′2
k′obs
k′4
4
5
9
10.7 ( 0.17
0.70 ( 0.20
0.19 ( 0.02
0.021 ( 0.004
0.36 ( 0.06
2.97 ( 0.12
0.55 ( 0.04
0.032 ( 0.004
0.049 ( 0.01
1.55 ( 0.06
0.35 ( 0.03
1.42 ( 0.06
0.20 ( 0.01
0.45 ( 0.06
0.25 ( 0.07
0.032 ( 0.009
0.089 ( 0.008
0.012 ( 0.005
0.071 ( 0.005
10
a
Data are means ( SD of three replicates.
transformation product found was thifensulfuron 2
(Bastide et al., 1994). This hydrolysis pathway was
different from the methyl metsulfuron pathway and
could be explained by the difference between thiophene
ring and benzene ring activation (Bastide et al., 1994).
Hyd r olysis Ra te of Th ifen su lfu r on (2) a t p H 9
a n d 10. The two compounds 6 and 7 were obtained by
hydrolysis of 2. In the case of chlorsulfuron and met-
sulfuron methyl, only the O-demethylation reaction was
reported (Sabadie, 1991; Reiser et al., 1991). At pH 9
(Figure 5A), the most important pathway was the hy-
drolysis of the sulfonylurea bridge. At pH 10 (Figure
5B), during a reaction time of <200 h, only 7 appeared.
Compound 6 could be formed by subsequent hydrolysis
of 7. To verify this hypothesis, the hydrolysis rates of
7 at pH 9 and 10 were measured, and the k values were
calculated as 3.2 × 10-4 h-1 and 4.86 × 10-4 h-1, re-
spectively. These results partially explain the formation
of 6 by hydrolysis of 7 in the hydrolytic reaction of 2.
F igu r e 3. Proposed acidic hydrolysis pathway of thifensul-
furon (2) in aqueous buffer solutions (pH 4 and 5) at 28 °C (k′
represents reaction rate constants).
DISCUSSION
The stability of thifensulfuron methyl (1) in aqueous
solution is markedly influenced by pH, and hydrolysis
is accelerated by acidic and, to a lesser extent, alkaline
conditions. The pH values studied are not necessarily
the best choice for correlation with agricultural soils,
but some experiments were conducted at pH 6 and 8
with thifensulfuron methyl (1), and the hydrolysis rates
were low (t1/2 ≈ 770 h at pH 8; t1/2 ≈ 2000 h at pH 6).
With these conditions, the hydrolysis pathways were
similar to those at others pHs, but it was not possible
to accurately determine the rate constant data of these
different pathways. Two hydrolysis pathways of thifen-
sulfuron methyl (1), observed with acidic conditions,
were in agreement with those reported for other sulfo-
nylureas with triazine substituted by a methoxy group
(Sabadie, 1990, 1991; Reiser et al., 1991). Two similar
hydrolysis pathways were obtained with thifensulfuron
2. The relative ratio of the two pathways is of the same
order of magnitude for the two compounds at pH 4 and
5; the breakdown of the sulfonylurea bridge is only
slightly more rapid than the O-demethylation reaction.
The hydrolysis of hydroxylated intermediates 4 and
7 also gives two pathways of transformation; they are,
hydrolysis of the sulfonylurea bridge and opening of the
triazine heterocycle. The latter reaction is pH depend-
ent [k4(pH 4)/k4 (pH 5) ) 8.4; k′4 (pH 4)/k′4 (pH 5) ) 7.1
for 4 and 7, respectively], and the former is less affected
by pH [k3 (pH 4)/k3 (pH 5) ) 3.8; k′3(pH 4)/k′3 (pH 5) )
4.4) for 4 and 7, respectively]. Moreover, the major
hydrolysis product of 4 was 5 at pH 4 and 3 at pH 5,
whereas 6 was the major product of 7 at pH 5. At pH
4, 7 gave an equal amount of 6 and 8. In the case of
chlorsulfuron and metsulfuron methyl, the selectivity
of these different reactions was not pH dependent
(Sabadie, 1990, 1991).
F igu r e 4. Hydrolysis of thifensulfuron (2) in pH 4 buffer
solution at 28 °C.
rates of these two compounds, 2 and 7, were similar.
The relatively low hydrolysis rate of thifensulfuron 2
at pH 4 may be related to the pKa of this compound, as
previously explained for 1 and 2.
Hyd r olysis Ra te of Th ifen su lfu r on Meth yl a t p H
9 a n d 10. The stability of thifensulfuron methyl in
alkaline aqueous solutions was pH dependent and
followed first-order kinetics (Table 3). However, for this
product, we did not observe a contraction of the sulfo-
nylurea bridge as in the case of rimsulfuron (Schneiders
et al., 1993), but rather hydrolysis of the ester function
(Smith et al., 1990; Cambon et al., 1992). The sole first
The hydrolysis of thifensulfuron methyl (1) in alkaline
condition is specific to this compound, leading to the

Thifensulfuron Methyl Hydrolysis
J. Agric. Food Chem., Vol. 44, No. 1, 1996 337
metabolite isolated was thifensulfuron (2), produced by
biological degradation (Smith et al., 1990; Cambon et
al., 1992). Thifensulfuron (2) was transformed by
chemical processes, and the pathway of transformation
could be the same as in aqueous solutions. However,
the sole metabolites identified in soil were 6 and 7. The
metabolite 8 was not observed. Either it was not formed
or it was easily degraded by microorganisms.
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F igu r e 5. Hydrolysis of thifensulfuron (2) in pH 9 (A) and
10 (B) buffer solutions at 28 °C.
Received for review April 3, 1995. Revised manuscript re-
ceived October 26, 1995. Accepted October 31, 1995.X
corresponding acid. The ester function of other sulfo-
nylurea herbicides was not easily hydrolyzable. The
resulting thifensulfuron (2) was subsequently slowly
hydrolyzed in alkaline conditions. In soil, the first
J F950194F
X Abstract published in Advance ACS Abstracts, De-
cember 15, 1995.