Degradation of Paraoxon and the Chemical Warfare Agents VX, Tabun, and Soman by the Metal-Organic Frameworks UiO-66-NH2, MOF-808, NU-1000, and PCN-777

Article abstract of DOI:10.1021/acs.inorgchem.7b01809

In recent years, Zr-based metal-organic frameworks (MOFs) have been developed that facilitate catalytic degradation of toxic organophosphate agents, such as chemical warfare agents (CWAs). Because of strict regulations, experiments using live agents are not possible for most laboratories and, as a result, simulants are used in the majority of cases. Reports that employ real CWAs are scarce and do not cover the whole spectrum of agents. We here present a comparative study in which UiO-66-NH₂, NU-1000, MOF-808, and PCN-777 are evaluated for their effectiveness in the degradation of paraoxon and the chemical warfare agents tabun, VX, and soman, in N-ethylmorpholine buffer (pH 10) as well as in pure water. All MOFs showed excellent ability to degrade the agents under basic conditions. It was further disclosed that tabun is degraded by different mechanisms depending on the conditions. The presence of an amine, either as part of the MOF structure (UiO-66-NH₂) or in the agent itself (VX, tabun), is the most important factor governing degradation rates in water. The results show that MOFs have great potential in future protective applications. Although the use of simulants provides valuable information for initial screening and selection of new MOFs, the use of live agents revealed additional mechanisms that should aid the future development of even better catalysts.

Full text of DOI:10.1021/acs.inorgchem.7b01809

Article
pubs.acs.org/IC
Degradation of Paraoxon and the Chemical Warfare Agents VX,
Tabun, and Soman by the Metal−Organic Frameworks UiO-66-NH2,
MOF-808, NU-1000, and PCN-777
Martijn C. de Koning,* Marco van Grol, and Troy Breijaert
TNO, Lange Kleiweg 137, 2288 GJ Rijswijk, The Netherlands
S
* Supporting Information
ABSTRACT: In recent years, Zr-based metal−organic frame-
works (MOFs) have been developed that facilitate catalytic
degradation of toxic organophosphate agents, such as chemical
warfare agents (CWAs). Because of strict regulations,
experiments using live agents are not possible for most
laboratories and, as a result, simulants are used in the majority
of cases. Reports that employ real CWAs are scarce and do not
cover the whole spectrum of agents. We here present a
comparative study in which UiO-66-NH2, NU-1000, MOF-
808, and PCN-777 are evaluated for their effectiveness in the
degradation of paraoxon and the chemical warfare agents
tabun, VX, and soman, in N-ethylmorpholine buffer (pH 10)
as well as in pure water. All MOFs showed excellent ability to
degrade the agents under basic conditions. It was further disclosed that tabun is degraded by different mechanisms depending on
the conditions. The presence of an amine, either as part of the MOF structure (UiO-66-NH2) or in the agent itself (VX, tabun),
is the most important factor governing degradation rates in water. The results show that MOFs have great potential in future
protective applications. Although the use of simulants provides valuable information for initial screening and selection of new
MOFs, the use of live agents revealed additional mechanisms that should aid the future development of even better catalysts.
they may serve as the key active material in future protective
applications, such as canisters,9 sensors,10 coatings,11 and
clothing.12−14
INTRODUCTION
■
Metal Organic Frameworks (MOFs) are a relatively new class
of crystalline solids with tunable properties such as porosity and
pore size.1,2 They are built by the formation of coordination
bonds between metal-ion or metal-oxide clusters (called
secondary building units (SBUs)) and polytopic organic linkers.
The Zr6(μ3-O)4(μ3-OH)4 SBU has been used to synthesize a
variety of MOFs that catalyze the hydrolysis of organo-
phosphate (OP) agents, including extremely toxic chemical
warfare agents (CWAs).3,4 These MOFs were accessible by
varying the shape, size, and number of carboxylate groups
present on the organic linker. As the Zr6 SBU can
accommodate a maximum of 12 carboxylates, the use of
different linkers creates MOFs with varying symmetries,
structures, and different physical and/or chemical properties.
For instance, UiO-66 is composed of terephthalic acid linkers
and the resulting structure contains 6 Å octahedral and 9 Å
tetrahedral pores with a Langmuir surface area of 1187 m2 g−1.5
In the defect-free (ideal) structure of UiO-66, all 12 nodes in
the SBU are occupied (12-connected). By changing the bitopic
linker used in UiO-66 to the tritopic benzene-1,3,5-tricarboxylic
acid linker, the 6-connected MOF-808 can be obtained.6 In a
similar fashion, the use of the tetratopic 1,3,6,8-tetrakis(p-
benzoic acid)pyrene (H4TBAPy) leads to NU-1000, in which 8
of the 12 nodes of the Zr-SBU are occupied.7,8 Because of the
ability of these types of MOFs to rapidly degrade OP agents,
The data reported so far revealed several factors that
influence degradation kinetics. It was found that a higher
catalytic activity can be achieved by using 6- or 8-connected Zr-
MOFs as those MOFs have more vacant sites (catalytic sites)
available on the SBU compared to 12-connected MOFs, such as
UiO-66, that rely on structural defects as catalytic sites.15,16
Other properties, such as pore size, were also found to be of
importance, presumably by providing easier access of the agent
to catalytic sites within the framework.17 The (partial)
substitution of linkers with basic amine groups17−19 as well as
postsynthetic treatment of MOFs with alkoxides,20 as
exemplified with UiO-66-NH2 (and the structurally related
UiO-67-NH2), resulted in higher catalytic activity compared to
the unmodified MOFs and enhanced catalytic activity in
unbuffered conditions (MQ). The pH of the buffer played a
role in the exchange rate of zirconium-bound water molecules
for OPs.21 The size of the MOF particles was found to have a
significant effect on the hydrolysis rates of OPs as more
surface/catalytic sites per weight unit of MOF become
accessible with smaller particles.22 Finally, degradation products
Received: July 15, 2017
© XXXX American Chemical Society
A
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Article
may give rise to catalyst poisoning and lowered turnover.13,23
All of the above was concluded from separate studies, and
although comparable conditions were used (0.45 M N-
ethylmorpholine (NEM) buffer), direct cross-comparisons of
MOF potency are difficult to make as a result of inevitable
interlaboratory differences or differences in batches of
synthesized materials. More importantly, examples of the use
of live agents with these MOFs are relatively scarce,3,20 because
of the restrictions that apply to most laboratories with the use
of such dangerous agents. Consequently, most of these MOFs
have been tested with CWA surrogates (usually dimethyl
methylphosphate (DMMP), or dimethyl 4-nitrophenyl-phos-
phate (DMNP)).
those already reported for simulants as data of the hydrolysis of
a broad range of live agents is currently lacking for the majority
of MOFs reported.3 In this respect, it is worth noting that tabun
has not previously been used in such experiments. Second, the
results led to a better understanding of the key features that
govern the effectiveness in the degradation of various CWAs
under different circumstances. Finally, we report that the
different chemical structures of CWAs gave rise to agent-
specific interactions with the MOFs and differences in the
mechanisms of degradation for some CWAs.
EXPERIMENTAL SECTION
■
MOF Syntheses. UiO-66-NH2,25 NU-1000,7 MOF-808,6 and
PCN-77724 were synthesized according to reported solvothermal
methods. Briefly, this method entails the heating of a mixture of a
Zr(IV) source (usually ZrOCl2, or ZrCl4) and the requisite linker in a
solvent (e.g., dimethylformamide) in a closed dram vial. In a number
of cases, a modulator is added in the form of a monodentate carboxylic
acid. These modulators (e.g., formic acid, trifluoroacetic acid, or
benzoic acid) occupy nonconnecting sites on the nodes and/or
influence the nucleation in the synthesis process. Activation of
synthesized materials (removal of solvents from the pores) was
accomplished by solvent-exchange, followed by application of heat
under vacuum.
We therefore decided to compare, under identical conditions,
the catalytic activity of UiO-66-NH2, NU-1000, and MOF-808
in the hydrolysis of several chemical warfare agents (Figure 1)
Figure 1. Structures of chemical warfare agents used in this study.
Degradation Experiments. Caution! CWAs (GA, VX, GD) are
extremely toxic compounds and experiments should only be conducted by
trained personnel in a laboratory that is permitted to use such agents.
The hydrolysis reactions were monitored by 31P NMR (64 scans, 2 s
relaxation delay) at 25−27 °C. The 0.92 mM MOF suspensions were
made by mixing 1−2 mg of MOF (0.83 μmol, MW NU-1000 =
2180.78, MOF-808 = 1353.71, PCN-777 = 3184.05, UiO-66-NH2 =
1754.15 g·mol−1) in a variable amount of 10% D2O/H2O or 0.4 M N-
ethylmorpholine buffer (in 10% D2O/H2O) via sonication for 5−10
min. To 450 μL of the MOF suspension (0.92 μM) was added 50 μL
of GA/GD/VX or diethyl p-nitrophenyl phosphate solution (50 mM
in dry acetonitrile), resulting in a 0.83 mM MOF/5 mM agent
suspension (ratio 1:6). The mixture was vigorously shaken for 10 s. A
sample (340 μL) of the suspension was transferred to an NMR tube (5
mm) and fitted with a trimethylphosphate containing insert. The
progress of the reaction was monitored with 3 min increments for 40
min. To measure conversion at 30 s, a reaction mixture was prepared
of different chemical nature (VX (P-S), GD (soman, P-F), GA
(tabun, P-CN) and POX (paraoxon, P-O). In addition, we
decided to include PCN-777 in this selection. PCN-777 is a 6-
connected MOF, built from 4-4′-4″-s-triazine-2,4,6-triyl-triben-
zoic acid linkers, and has the same topology as MOF-808, but
with larger pore sizes.24 This MOF was not previously
evaluated as a catalyst in the hydrolysis of OP agents. The
degradation reactions were carried out by monitoring (31P
NMR) the conversion of agent when mixed in excess with a
MOF either in a basic solution (0.4 M N-ethylmorpholine
(NEM), adopted from previous reports) or in unbuffered
conditions (pure water). We here report the results of these
experiments. First of all, the degradation studies complement
Table 1. Summary of Kinetic Data and Maximum Conversions (after 40 min) Obtained in the Degradation Reactions of POX,
GD, VX, and GA in NEM Buffer (pH 10) and Water, by the MOFs NU-1000, MOF-808, PCN-777, and UiO-66-NH2 (pH 2.8−
4.4)
conditions
NEM
MQ
a
a
agent
POX
MOF
k, min−1
t1/2, min
conv , %
k, min−1
t1/2, min
conv , %
NU-1000
0.27
0.19
0.19
0.02
n.d.
n.d.
n.d.
n.d.
0.13
n.d.
n.d.
0.32
n.d.
n.d.
n.d.
n.d.
2.6
3.6
3.6
35
100
100
100
n.d.
n.d.
n.d.
n.d.
99
n.d.
n.d.
n.d.
21
MOF-808
PCN-777
n.d.
n.d.
a
UiO-66-NH2
NU-10008
MOF-808
PCN-777
75
0.007
n.d.
GD
VX
GA
<1
100
100
100
100
100
100
100
100
100
100
100
100
n.d.
n.d.
n.d.
n.d.
8.7
6.3
17.3
5.0
97
<2
<2
<2
<2
77
<1
n.d.
<1
n.d.
UiO-66-NH2
NU-1000
<1
n.d.
5.3
<0.5
<0.5
2.2
<1
0.081
0.11
MOF-808
PCN-777
73
0.040
0.14
34
UiO-66-NH2
NU-1000
85
0.0072
0.0074
0.019
0.018
23
MOF-808
PCN-777
<1
94
24
<1
37
37
UiO-66-NH2
<1
39
33
a
Conversion within the experimental time frame.
B
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under identical conditions and filtered using a 0.2 μM HPLV filter
after 30 s.
were generally slower than those reported previously for the
structurally similar agent dimethyl-4-nitrophenylphosphate
(DMNP).8,15,17,18 POX, which is larger than DMNP, may
experience more difficulty accessing pores and reaching
catalytic sites. Differences could also be invoked by small
differences in UiO-66-NH2 batches reflected in structural
defects (catalytic sites) and particle size or by the use of a
slightly different protocol.
The background hydrolysis rate of soman (GD) in NEM
buffer (without MOF) proceeded with a half-life between 12
and 15 min (see the SI). However, in the presence of any of the
MOFs tested, extremely fast hydrolysis into pinacolyl
methylphosphonate was observed, resulting in 100% con-
version after the first time point (see the SI). In sharp contrast,
when the reactions were carried out in MQ, no degradation of
GD was recorded. Even UiO-66-NH2 did not show any
catalytic activity in this case, which may seem unexpected given
the observed hydrolysis of POX (albeit slow) and the slightly
more labile P−F bond compared to a P−O bond. Perhaps the
differences are invoked by different energies associated with
coordinative- and/or hydrogen bond based binding of the
agents to the Zr-nodes as was recently demonstrated, using
computational methods, for DMNP and GD/VX analogues in
combination with NU-1000.8 The results further clearly
illustrate the necessity of the presence of an adjuvant in the
case of GD hydrolysis, for instance, in the form of a basic buffer.
The hydrolysis of VX was greatly enhanced by the presence
of all MOF catalysts in NEM buffer (Figure 3a). In this case,
Control experiments were conducted in an identical manner, but in
the absence of MOF material (background hydrolysis of agent).
Data Analysis. The percentage hydrolysis at each time point was
determined by dividing the 31P NMR integral(s) of the signal(s) of the
hydrolysis products by the sum of all 31P integrals (and multiplying
with 100). The time point values were defined as the time of
measurement start plus 1.5 min (total measurement time per time
point was 3 min). Initial hydrolysis rates were determined by plotting
the natural log of the averaged agent concentrations (of duplicate or
triplicate measurements) vs time and taking the slope (−k) of the
fitted straight line to calculate the half-life using the equation t1/2 = ln
2/k. In some cases, curves could not be fitted due to half-lives (much)
lower than the time required for measurements. In those cases, half-
lives were estimated by assuming that at least 6 half-lives had passed
(<2% remaining agent) at the first time point. In other cases,
attenuated hydrolysis rates at later time points were observed
(resulting in biphasic curves and sometimes reduced final conversion
percentages). In those cases, the initial hydrolysis rates (k) and
associated half-lives were estimated by fitting the first couple of time
points only.
RESULTS AND DISCUSSION
■
The results of the degradation experiments are presented per
agent and are displayed in separate graphs for reactions in
NEM buffer and in water. Table 1 summarizes the initial
hydrolysis rates (k, min−1), the half-lives (t1/2, min), and the
maximum conversion percentages. Data that repeats previously
reported work is marked with a reference.
The results of the hydrolysis of paraoxon (POX) in the
presence of the MOF catalysts are depicted in Figure 2. In
NEM buffer (Figure 2a), NU-1000, MOF-808, and PCN-777
showed comparable activity (with half-lives ranging between 2
and 4 min). UiO-66-NH2 gave much slower hydrolysis rates
(t1/2 ≈ 35 min) of POX. In contrast, UiO-66-NH2 was the only
MOF to display some hydrolytic activity toward POX in MQ
(Figure 2b). The hydrolysis rates of POX into diethylphosphate
Figure 3. Degradation rates of VX in the presence of several MOFs in
(a) NEM buffer and (b) in water.
the presence of MOF-808 and PCN-777 resulted in extremely
fast hydrolysis rates which led to complete degradation of VX
into ethyl methylphosphonate (EMPA) within the first time
point (5.5 min). Attempts were made to obtain data for earlier
time points by filtering off the MOF after 30 s of reaction time;
however, due to the rapid reaction and the relatively long time
required (when compared to 30 s!) to conduct the filtration
Figure 2. Degradation rates of ethyl-paraoxon in the presence of
several MOFs in (a) NEM buffer and (b) in water.
C
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step, the experimental error is rather high. Nevertheless, for
MOF-808 and PCN-777, the half-lives were estimated to be
less than half a minute. The high rates observed may be partly
explained by the higher availability of catalytic zirconium sites
(lower connectivity) in MOF-808 and PCN-777 compared to
NU-1000 and UiO-66-NH2 as well as their increased
accessibility because of the larger pore sizes in both MOF-
808 and PCN-777. Any influence of the differences in pore size
between MOF-808 and PCN-777 could not be established
because of the inability to distinguish between the hydrolysis
rates of these two MOFs with the method used. UiO-66-NH2
and NU-1000 showed very fast hydrolysis rates in NEM buffer
too, with half-lives of 2.2 and 5.5 min, respectively. Although
NU-1000 has more and better accessible catalytic sites
compared to UiO-66-NH2, the latter clearly benefits from the
presence of the amine.
Figure 4. Probing the role of the amine group in VX in the
degradation reaction. Comparison of the degradation rates of VX, a
VX-Me in the presence of NU-1000 under various conditions. The
data of VX-Me in the presence of DiPEA were corrected for
spontaneous hydrolysis of VX-Me.
A striking observation was that, when the reactions were
carried out in MQ, all MOFs were able to mediate VX
hydrolysis with half-lives varying between approximately 9 and
17 min (Figure 3b). This is in sharp contrast with the results
obtained with GD and POX in MQ, in which only UiO-66-
NH2 showed some activity when reacted with POX. Also, in the
case of VX, UiO-66-NH2 stands out as the best performing
MOF tested in MQ with a half-life of only 5 min. Further, it
was found that PCN-777 performed worse than MOF-808 in
MQ, which was unexpected as PCN-777 has a larger pore size
than the isoreticular MOF-808, thus providing even more
opportunity for enhanced diffusion rates of agent in the pores
or accessibility of Zr-nodes. This result may stem from a
somewhat lower quality MOF obtained as a result of using
heat-vacuum activation instead of scCO2-activation26 (which
required equipment that was not available), leading to a
reduced BET surface area measured for PCN-777 as compared
to reported values of PCN-777 and MOF-808 (see the SI).
Another factor that may have contributed to the lower activity
of PCN-777 is its slightly larger particle size (2−6 μM)
compared to MOF-808 (∼1 μM).
proximity driven assistance) of the amine moiety of VX when
bound to NU-1000. The same mechanism is probably also
involved in the previously reported hydrolysis of the VX-related
compound EA-2192 by UiO-67.19
In this respect, it is of importance to note that the very toxic
EA-2192 (a.k.a. des-ethyl VX or V27a, obtained when the OEt
group in the VX structure is replaced with an OH group) could
not be detected in the degradation experiments with 31P NMR.
Thus, VX hydrolysis exclusively led to the formation of the
relatively nontoxic ethyl methylphosphonate (EMPA) in all
cases, which is in line with earlier findings.19
The reaction of tabun (GA) in NEM buffer in the presence
of each of the MOFs gave similar results as with GD. Thus, the
degradation of GA is greatly accelerated by the MOFs in NEM
buffer, with respect to the background reaction (t1/2 ≈ 35 min),
leading to complete disappearance of tabun at the first time
point in all cases (see the SI). In all of these reactions, a single
product with a resonance at 11 ppm (31P NMR) was formed.
LC tandem HR-MS/MS analysis of the filtered reaction
mixture revealed that this product was dimethylphosphoramidic
acid monoethylester (Figure 5).
The intriguingly facile hydrolysis of VX in MQ, compared to
the other agents, may in part be explained by the previously
computed thermodynamic preference for hydrolyzing the P−S
(−123 kJ/mol) bond over the P−O bond (−79 kJ/mol) and
P−F bond (−83 kJ/mol) upon coordinative binding of the
agents to the Zr6-nodes.8,19 However, we hypothesized that the
hydrolysis rate of VX was also enhanced by the presence of a
basic amine (pKa ∼ 8.5) in the VX structure itself and/or in the
second breakdown product 2-(diisopropylamino)ethanethiol
(DESH). The involvement of this amine moiety was evidenced
by the observation that VX-Me, which is the nonbasic, N-
alkylated derivative of VX, was not hydrolyzed by NU-1000 in
MQ (Figure 4, closed circles). As a control, VX-Me was also
treated with NU-1000 in the basic NEM buffer, which led to
rapid hydrolysis, as expected (Figure 4, open circles). As each
VX molecule carries only 1 basic amine, the hydrolysis rates of
VX by NU-1000 (and all other MOFs) in MQ were quite
remarkable. This efficiency may be explained by the close
proximity of this amine to the catalytic site upon binding of
intact VX in the MOF. Indeed, the addition of 1 equiv of
diisopropylethylamine (DiPEA), representing the basic part of
DESH, to a mixture of NU-1000 and VX-Me in MQ enhanced
the hydrolysis rate of VX-Me (Figure 4, squares), but not as
high as with VX itself (Figure 4, triangles). The added DiPEA
acts by intermolecular assistance which is expected to be less
effective than the intramolecular assistance (or at least close-
Figure 5. Structures of tabun and the observed hydrolysis products of
tabun in the reaction with MOFs. (a) Identified using LC-HR-MS/
MS. (b) Identity confirmed by spiking with an authentic sample. (c)
Reference 27.
When the experiments were performed in MQ, tabun was
degraded by all MOFs (Figure 6), similarly but more slowly as
observed with VX in MQ. The integral measurements in these
31P NMR experiments were slightly less accurate because
multiple hydrolysis products were formed simultaneously which
led to lower signal-to-noise ratios. Following a similar reasoning
as with VX in MQ, the slow, but apparent, hydrolysis of tabun
in the MQ experiments can be ascribed to assistance of the
dimethylamine function in tabun or by released dimethylamine
in solution. UiO-66-NH2 and NU-1000 mediated reactions led
to the formation of predominantly ethyl phosphate (0.4 ppm,
Figure 5), while MOF-808 gave a mixture of products with
resonances at 0.4 ppm (minor) and 3.7 ppm (major). The
D
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larger pore size of PCN-777 compared to MOF-808, while
having the same topology and connectivity, played no
significant role for catalytic degradation. Probably, the pore
size of MOF-808 was already sufficient, allowing efficient entry
of the organophosphates into both frameworks.
When executed in MQ, organophosphate hydrolysis was
slower or even absent, and often incomplete. The incomplete
degradation can be ascribed to catalyst poisoning, in which the
CWA degradation products occupy catalytic sites.13,20,23 UiO-
66-NH2 was the best performing MOF in MQ. Although the
small particle size of this MOF (which was about 10 times
smaller than that of the other MOFs) presumably contributed
to its enhanced catalytic activity,22 it is likely that the presence
of the amine function is a major contributor17−20 and that the
presence of a basic function is more important than a higher
number of catalytic sites in the other MOFs. The latter
observation was further exemplified by the previously
undiscovered notion that a basic function in the agent (VX,
and to a lesser extent, tabun) also had a beneficial effect on
hydrolysis rate of the agents. The degradation of VX by all
MOFs in MQ proceeded via a close-proximity driven18 or
intramolecular involvement of the amine group in the VX
structure.
POX, GD, and VX showed selective hydrolysis (if any) of the
respective P−OAr, P−F, and P−S bonds, giving the
corresponding phosphoric (in the case of POX) and
phosphonic (in the case of GD, VX) acids, in both NEM
buffer and MQ. While the P−CN bond in tabun was selectively
hydrolyzed in NEM buffer, multiple simultaneous hydrolysis
routes were recorded in MQ (cleavage of P−CN, P−NMe2, or
both) and is probably dependent on the pH.
Figure 6. Degradation rates of tabun in the presence of several MOFs
in water.
latter product was identical to the one obtained in NEM buffer,
but the 31P resonance was shifted because of the difference in
pH between the two types of samples (pH 10 vs pH 4), which
was confirmed by diluting an aliquot of the MQ sample in
NEM buffer, resulting in shifting of the 3.7 ppm peak to 11
ppm (and the ethylphosphate resonance from 0.4 to 3.4 ppm;
see the SI). The simultaneous formation of several products in
the hydrolysis of tabun can in part be explained by the various
leaving groups that tabun possesses. On the other hand, the
selectivity of hydrolysis may result from subtle differences in
pH in the individual (unbuffered) experiments. The latter was
concluded by the observation that the use of PCN-777 led to a
mixture of products at 0.4 ppm (ethylphosphate) and −20
ppm, which could be assigned27 as phosphorocyanidic acid
monoethyl ester. The unexpected difference in selectivity of
hydrolyzation of tabun with this MOF may have been invoked
by the more acidic conditions (pH 2.8) observed in the
reaction with PCN-777 compared to the other MOFs (pH
3.9−4.4, measured after 1 h of reaction time).
While the use of simulants in the evaluation of the catalytic
activity of MOFs remains highly useful for initial screening and
selection of MOF catalysts, the results presented here show that
evaluation with live agents of different chemical nature provides
additional insights into the mechanisms involved in the
degradation of specific agents, which should prove useful in
the future engineering of MOFs in protective applications.
A fair comparison of MOF potency is difficult to make, as the
results show that several mechanisms are running in parallel,
depending on the type of MOF used and the reaction
conditions employed. In addition, the hydrolysis of tabun
into ethylphosphate required 2 consecutive hydrolysis reac-
tions, further complicating kinetic analyses.
ASSOCIATED CONTENT
* Supporting Information
■
CONCLUSIONS
S
■
The degradation rates of the chemically diverse range of
organophosphate based chemical warfare agents VX, tabun,
soman, and ethyl-paraoxon were measured in the presence of
four Zr-based metal−organic frameworks under identical
conditions. Three of the four MOF catalysts employed (UiO-
66-NH2, MOF-808, and NU-1000) were previously reported to
degrade OP agents, while the use of PCN-777 as a catalyst is
reported here for the first time. The degradation rates were
measured in an alkaline-buffered system (0.4 M N-ethyl-
morpholine, pH 10) or in water in order to compare the
potential of the MOFs in the degradation reactions under
different circumstances and to further uncover the features and
mechanisms that govern these detoxification reactions. The
experimental data showed that all Zr-based MOFs had great
potential for the destruction of the various agents in an alkaline-
buffered system. For some agents (GD, GA), conversion rates
were so high that differences between MOFs could not be
distinguished. In those cases, altered conditions should be
considered, such as the use of higher agent/MOF ratios. In
cases where differences in potency could be measured (POX,
VX), it seems that MOFs with lower connectivity (higher
amount of available catalytic sites) have the advantage. The
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b01809.
Synthesis and characterization of MOFs (BET surface
areas, particle sizes, SEM images), hydrolysis curves of all
MOF/agent/condition combinations and corresponding
kinetic plots, and selected 31P NMR spectra and mass
spectra used to identify tabun hydrolysis products (PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail: m.dekoning@tno.nl.
■
ORCID
Martijn C. de Koning: 0000-0001-6482-9502
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors thank the Dutch Ministry of Defense for funding
this project as part of the V1408 CBRN program.
E
DOI: 10.1021/acs.inorgchem.7b01809
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
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UiO-66-NH 2. Chem. Sci. 2015, 6, 2286−2291.
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DOI: 10.1021/acs.inorgchem.7b01809
Inorg. Chem. XXXX, XXX, XXX−XXX