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Anion Binding Self-Assembly of Polypyrrolic Macrocycles.

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[12] A. F. Cameron, D. W Taylor, R. H. Nuttall, J. Chem. SOC.Dalton Trans 1972,
1603.
[13] The presence of acetonitrile is supported by I R spectroscopy. The band at
i' = 2252 c m - ' is assigned to a C-N
stretch: K. Nakamoto, Infrared Spectra
o j Inurgunic and Coordination Compciunds, 2nd ed., Wiley, New York, 1970,
p. 186.
[I41 J A. R. P. Sarma, G. R. Desiraju, Arc. Chem. Res. 1986, 19, 222.
[15] C. A. Hunter, Angeiv. Cheni. 1995, 107, 1181; Angnv. Chem. Int. Ed. Engl.
1995, 34, 1079; M Fujita, J. Yazaki, K. Ogura, J. Anz. Chem. Sor. 1990, 112,
5645; P. J. Stang, D. H. Cao. ibid 1994, 116, 4981; R. V. Slone, D. 1. Yoon,
R. M. Calhoun, J. T. Hupp, ihid. 1995, 117, 11813; P. J. Stang, B. Olenyuk.
Angew. Chem. 1996, 108, 798; Angeii. Chem. Int. Ed. Engl. 1996, 35,732.
Anion Binding:
Self-Assembly of Polypyrrolic Macrocycles**
Jonathan L. Sessler," Andrei Andrievsky,
Philip A. Gale, and Vincent Lynch
In memory of Professor Emanuel Gil-Av
The self-assembly of complementary fragments occurs
throughout Nature and plays an essential role in the construction of such biological "superstructures" as nucleic acids (for
example their duplexes and complexes with peptides), multicomponent enzymes, cell membranes, and viral capsids.['] The
structural information required for facile self-assembly is preprogrammed in the topography and functionality of the building block surfaces. These small subunits bind together reversibly
through multiple weak noncovalent interactions. This minimalistic yet effective approach to molecular architecture has challenged supramolecular chemists to design systems capable of
recognition, self-assembly, replication, and transport.[2.31 However, it has not been until recently, that the first abiotic selfassembling supramolecular aggregates were reported.12 ']
Most notably, many of the structural motifs discovered were
employed for production of the "functioning structures" such as
interlocked r n ~ l e c u l e s(capable
~~~
of switching, information
storage, and electron transfer), noncovalent dimers (capable of
encapsulation['] and bindingr6]of small molecules), molecules
capable of ~elf-replication,['~noncovalent dendrimers,['I
helices, racks, ladders, and grids,[3a1nanotube-forming cyclic
peptides,'']
molecular zippers,["]
oligonucleotide-based
supramolecular assemblies," 'I monolayers, multilayers, and
vesicles,[' ordered solid-state s t r ~ c t u r e s , [ ~13]
~ - and
~ . selfassembled photoactive aggregate^."^] Noncovalent forces
used to generate these arrays include hydrogen bonding,
metal-ligand coordination, X-x stacking, and hydrophobic
interactions. On the other hand, there are but few self-assembled
supramolecular systems that are predicated on anion chelation."'] These include chiral bicyclic guanidinium dimers and
tetramers that assemble into a double helix around sulfate template~,['~"'copper(1r)-arginine complexes that form chiral
double-helical structures with aromatic dicarboxylates," 5b1 selfassembling diamidopyridinium phosphates," 5c1 and dianionic
-'
[*I
[**I
Prof. J. L. Sessler, A. Andrievsky, Dr. P A. Gale, V. Lynch
Department of Chemistry and Biochemistry
The University of Texas a t Austin
Austin, TX 78712 (USA)
Fax: int. code +(512) 471-7550
e-mail: sessler~mail.utexas.edu
This research was supported by the National Institutes of Health (grant A1
33577) and National Science Foundation (grant CHE 9122161). P. A. G. wishes t o thank the Fulbright Commission for a post-doctoral research scholarship.
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and dicationic moieties that form self-assembled infinite
rods." 'dl In all cases, the resulting complexes contain a minimum of two different components, one of which is an anion.
It occurred to us that the anion binding properties of expanded porphyrins such as sapphyrins (e.g. 1)['61 could be effectively
employed for the self-assembly of novel supramolecular species.
In particular, we speculated that the previously synthesized
zwitterionic sapphyrins 1a and 1c , [ ' ~ which
~]
contain anionic
carboxylate groups attached to a protonated sapphyrin core,"']
but which are precluded from "biting their own tails," due to the
length of the carboxylate-sapphyrin spacer, should self-assemble
readily. This assumption was made on the basis of our previous
finding that sapphyrins, when protonated, effectively chelate
carboxylate ions through a combination of hydrogen bonding
and electrostatic attractions involving the pyrrolic hydrogens
and the ligated oxyanion.['6b.'1 Herein we report that this is
indeed the case in the gas phase, in solution, and in the solid
state. Taking this methodology a step further, and exploiting
our recent discovery that calix[4]pyrroles (a class of molecules
known for over a century["]) are capable of anion chelation
through multiple hydrogen bonds,['g1 we have synthesized a
new calix[4]pyrrole with a carboxylate pendant arm, and found
that these purely anionic species also self-assemble. In contrast
to the previously reported anionic systems capable of self-assembly," the sapphyrin- and calix[4]pyrrole-based carboxylate building blocks of this report are self-complementary, and
thus, no other extra components are required for self-assembly.
Calix[4]pyrrole monoacid 2 a was synthesized by the acidcatalyzed condensation of methyl 4-acetylbutyrate and cyclohexanone with pyrrole. This produced the monomethyl ester
2b in 12% yield (after chromatographic purification). Subsequent hydrolysis of 2 b (sodium hydroxide ethanol/water solution at reflux; see Experimental Procedure) afforded the
monoacid 2a, which was immediately converted to its tetrabutylammonium or trimethylammonium salts (see Experimental Procedure).
0
la: R'=R2=CH,;
4
R3=H; R4=CH2CO2H
l b R' =R2=CH3; R3=H; R4=CHzC02CH,
l c : R'=R2=CH2C02H; R3=R4=CH3
2a: R = (CH&C02H
2b: R = ( C H ~ ) B C O ~ C H ~
1d: R' = R2 = CH2CO2CH,; R3 = R4 = CH,
Initial evidence for self-assembly in the gas phase came from
low- and high-resolution fast atom bombardment (FAB) mass
spectrometry. Intense peaks for the dimer (but not trimer or tetramer) at double the molecular weight were observed for the
carboxylates l a , l c , and 2a(Fig. 1). Such peaks, however, were
not seen with "control" methyl esters 1b, I d , and 2b. This indicates that the presence of unprotected carboxylate groups in the
molecule is essential for self-assembly, and rules out formation
of dimers due to simple van der Waals or hydrophobic attractions between the macrocycles. In addition, and in support of the
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Angew. Chem. Int. Ed. Engl. 1996, 35. No. 23124
vealed that the appended macrocycle forms a supramolecular
dimer in the solid state (Fig. 2a). A carboxylate “hook” from
one molecule of l c is chelated to the pyrroIe core of the second
macrocycle. Simultaneously, this second macrocycle shares its
carboxylate “tail” with the first sapphyrin subunit. A trifluoroacetate ion is coordinated to each of unchelated faces in the
dimer and prevents these sites from being involved in further
binding. Perhaps as a result of this, the second carboxylic acid
is not bound to a sapphyrin core, but is coordinated to a
methanol molecule. The macrocycles of the dimer are related by
a crystallographic inversion center at 1/2, 1/2,0. The separation
between the root mean square (RMS) planes of the nitrogen
atoms in this structure is 3.39(1) A.
X-ray quality crystals of the tetrabutylammonium salt of calix[4]pyrrole carboxylate 2 a were obtained by slow evaporation
of a solution of 2a in dichloromethane in the presence of excess
tetrabutylammonium fluoride trihydrate.[* The resulting crystal structure confirmed that this anionic calix[4]pyrrole also selfassembles into dimers in the solid state. In this instance, in
analogy to the sapphyrin case, the carboxylate moiety is hydrogen-bonded to the pyrrole array of an adjacent calix[4]pyrrole
(Fig. 2b). Now, however, the separation between the RMS
planes of the nitrogen atoms in each macrocycle is 7.41(1) A.
The calix[4]pyrrole 2a adopts a cone conformation in the dimer,
as is observed in the anion complexes of related systems.[’91
la
’O01
I
-I
,Oi
500
630
I
la-la
I
1261
I
900
700
1100
1300
mlz
lc
lc.lc
20-
1377
0
500
900
700
1100
1300
mlz
Fig. 1. FAB mass spectra of sapphyrin carboxylates.
versatility of the zwitterionic and anionic self-assembly of
sapphyrin and calix[4]pyrrole carboxylates, all possible supramolecular heterodimers were detected by mass spectrometry
when two different species (i.e. 1 a, 1 c, and 2 a) were mixed in a
ratio of approximately 1 :1 prior to FAB MS analysis (Table 1 ) .
Table 1. Molecular masses of selected homo- and heterodimers.
Dimer
M(found)
M(calcu1ated)
~ l a . 2 a [b] l c . 2 a [a]
l a . l a [a] I c . l c [a] 2 a . 2 a [b] 1 a . l [a]
1260.7595 1376.7737 1239.8087 1318.7679 1249.7775 1308.7961
1260,7616 1376.7726 1239.8102 1318.7671 1249.7820 1308.7953
[a] Positive ion FAB mass spectrometry. [b] Negative ion FAB mass spectrometry.
As a further test of the proposed self-assembly process, experiments were carried out in the presence of fluoride ion. Since
protonated sapphyrins have a significantly higher affinity for
fluoride ion than other anions,[’6e1 it was expected that the
addition of fluoride ion would inhibit sapphyrin dimer formation in the gas phase. This proved to be the case. When tetrabutylammonium fluoride was added to the samples of sapphyrin mono- and/or dicarboxylates, the peaks in the mass
spectra ascribed to the dimer species disappeared completely. In
the case of 2a, addition of tetrabutylammonium fluoride decreased the intensity of the dimer ion peak but did not eliminate
it completely.
Of sapphyrin carboxylate
were ObX-ray
mined by slow diffwbn of ether into a solution of 1c in
dichloromethane/methanol (3/1) [.’‘I
The structure analysis reAnPex,. Cltem. Int. Ed Engl. 1996,35, No. 23/24
0 VCH
Fig. 2. Side view of the supramolecular sapphyrin dimer I c - l c (a) and of the
noncovalent calix[4]pyrroledimer 2 a . 2 a (b) in the solid state (thermal ellipsoids are
scaled to the30% probabilitylevel). C: black, H . llght blue, N: blue, 0:red, F: green.
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The ‘H N M R spectra of sapphyrin monocarboxylate 1a in
[D,]methanol o r CDCI,, and dicarboxylate l c in a [DJ
rnethanol/CDCl, (2/1) mixture[221showed strong line broadening. which is consistent with self-aggregation of these species.[231
Dilution experiments performed over a concentration range of
50 to 5 mM in these solvents showed little change in the spectra,
which is taken as an indication that the putative aggregates
prevail over the monomers at these concentrations even in these
highly polar solvent mixtures.
In order to determine the stoichiometry of aggregation, vapor
pressure osmometry (VPO) measurements were carried out in
1,2-dichloroethane using compound 1 a. The average molecular
weight of the species in solution determined by this method
( M =I281 gmol-‘; calculated 1261 gmol-’) corresponds to
that of the dimer. In contrast, these same VPO measurements
carried out under identical conditions with the control sapphyrin methyl ester 1b confirmed its monomeric state in solution ( M = 690 gmol- calculated 643 gmol-’).
Fluoride inhibition of sapphyrin dimerization was also studied by * H N M R spectroscopy. This was done by adding aliquots
of tetrabutylammonium fluoride trihydrate solution (up to 3
equiv) to stock solutions of the sapphyrin carboxylates 1 a and
l c , and recording the resulting changes in the proton N M R
spectra. Generally, upon addition of fluoride ion, the spectra
became well-resolved and all sapphyrin proton signals were seen
to shift. The signals of the ethylene protons of the linker between
the sapphyrin macrocycle and its carboxylate pendant arm were
found to be particularly diagnostic. These, undergo downfield
shifts on addition of fluoride ion (la: 6 = 1.67 and 1.07 for
CH,CH,CO ;and CH,CH,CO,, r e ~ p e c t i v e l y ) . [These
~~,~~~
signals are the ones most affected by the ring current of the
“partner” aromatic sapphyrin macrocycle, and are thus the
most indicative of dimer break-up. This is because in solution,
as in the solid state, the dimers are probably held together in an
offset manner. Such a binding arrangement would force the
protons of the ethylene “arm” to resonate at higher field. When
fluoride ion is added in sufficient quantities (generally less than
2 equiv), it binds to the sapphyrin cavity and displaces the carboxylates. This breaks the dimers and reestablishes the “normal” lower field chemical shift for the ethylene proton signals
(Fig. 3).
’
would be expected upon break-up of the calix[4]pyrrole aggregates. From these experiments it is thus inferred that, as was true
for sapphyrins 1 a and 1 c, conditions can be found under which
dimerization is precluded.
In conclusion, anion-binding interactions may be used as a
means of effecting the spontaneous self-assembly of appropriately designed supramolecular ensembles. This is important because it shows yet one more way in which a simple to control
recognition motif (in this case sapphyrin- or calix[4]pyrrolebased anion binding) may be used to “program in” information
that encodes for the self-controlled construction of higher order
structures that, in turn, display considerable molecular complexity.
Experimental Procedure
2b: Methyl 4-acetylbutyrate (0.80 g, 5.6 mmol), cyclohexanone (0.55 g. 5.6 mmol),
and pyrrole (0.75 g, 11.2 mmol) were dissolved in methanol (50 mL), and the mixture cooled to OiC. Methanesulfontc acid (0.5 mL) was added dropwise over the
course of five minutes, and the mixture stirred at 0 ° C for 1 h and then at room
temperature overnight. The solvent was removed in vacuo. FAB mass spectra
showed the presence ofmono-, di-. tri-, and tetrafunctionahzed material in thecrude
reaction mixture. Chromatographic purification (silica gel, dichloromethane) yielded 2b a s a white foamy solid (211 mg, 0.33 mmol. 12%). ‘H NMR (250 MHz,
CDCI,): 6 =7.07 (br. m, 4H, N H ) , 5.88 (m. XH, pyrrole C H ) . 3.63 (s, 3H. OCH,),
2.22 (t. J =7.2 Hz, 2H, CH2), 1.93 (br., 14H, 6CH,(cyclohexyl). CH,(hook)),
1.56-1.35 (br., 23H, CH,(hook) +9CH,(cyclohexyl) +CCH,). The term hook
refers to the propionic acid side chain. ’,C NMR (62.9 MH7, CDCI,): 6 = 173.8,
137.2, 136.5. 136.3, 130.7, 103.6, 103.5 103.2, 53.4.51.4,39.7. 39.5, 39.4.38.5. 37 5,
37.2. 36.9, 36 8,34.0,26.1, 25.9, 22.8.22.7. 19.9. CI MS: mi: 635 (MH’); HRMS:
calculated for C,,H,,N,O,:
m / z : 634.4247; found. 634.4236; elemental analysis:
C 77.56, H 8.57, N 8.82; found: C 77.41. H 8.50, N
calculated for C,,H,,N,O,:
8 84.
2a. Methyl ester 2 b (211 mg, 0.33 mmol) in ethanol (20 mL) was heated to reflux.
Aqueous sodium hydroxide (20 mL, 2.OM) was then added and the mixture stirred
at reflux for 4 h. The solution was allowed to cool and ethanol removed in vacuo.
After acidification with perchloric acid (70%). the product was extracted with
dichloromethane (50 mL). The organic layer was then washed with water (100 mL)
and dried over MgSO,. Removal of the solvent afforded La as a white foamy solid
(187mg, 0.30mmo1, 91%). ‘ H N M R (250MHz, CDCI,): 6 = 7 . 0 2 (br. m. 4H,
N H ) . 5.89 (m, XH, pyrrole C H ) , 2.26 (t. 2H. CH,). 1.91 (br m, 14H,
6CH2(cyclohexyl) +CH,(hook)). 1.44 (br. m, 24H. 9CH,(cyclohexyl) +CH,(hook) +CCH, +0.5H20).The term hook refers to the propionic acid side chain.
’,C N M R (62.9 MHz, CDCI,): 6 =179.4, 137.3, 136.6, 136.2, 103.7, 103.6, 103.5.
103.2, 53.4, 39.7, 39.4, 39.3, 38.5, 37.4, 37.2, 36.9. 36 8, 33.8. 26.0, 25.9. 22.7, 22.6.
19.5. FAB MS: m / r : 620 (mi).
HRMS: calculated for C,,H,,N,O,:
mjz:
620.4090; found 620.4073; elemental analysis: calculated for <‘,,H,,N,O,: C 77.38,
H 8.44, N 9.02; found: C 76.78, H 8.42, N 8.92.
+
The tetrabutylammonium salt of Z a was precipitated in quantitative yield from a
solution of 2 a in diethyl ether by the addition of tetrabutylammonium hydroxide
(2.0 equiv). It was then washed with ether and water followed by drying in vacuo.
Elemental analysis: calculated for C,,H,,N,O,-H,O- C 76 40, H 10.19. N 7.96;
found. C 76.58, H 10.04, N 7.95.
Fig. 3 Schematic rcpresentation of the sapphyrin 1 a, dimerization, and fluoride
ion inhibition thereof. Green blocks: sapphyrin 1 a ; red blocks: carboxylate appendages of l a : blue block: fluoride ion.
The trimethylammonium salt of 2 a was obtained by passing trimethylamine gas
through a methanolic solution o f Z a a t - I O ~ CThesalt
.
precipitated in quantitative
yield and was then dried in vacuo. Elemental analysis: calculated for
C4,H,,N,O;1~3(H2O): C 75.18. H 9.18, N 10.19; found: C 75.00, H 8.97. N 10.10.
Received. June 17, 1996 [29234IE]
German version: Angen Chem. 1996, IOX, 2954-2957
Unfortunately, the low solubility of the trimethylammonium
salt of 2a in organic solvents precluded a quantitative ’H N M R
analysis of this system. However, a ROESY N M R spectrum of
of a suspension of this salt in CD,CI, provides evidence for
association of the calix[4]pyrrole anions in solution. For instance. two resonances are observed between 6 =7.0 and 1.5.
These are typical shifts for N H protons in other noncomplexed
cali~[4]pyrroles[’~~
and are thus assigned to the signals of N H
protons in the calix[4]pyrrole monomer. In addition, a broad
resonance is observed at about 6 = 11, which is ascribed to an
exchange peak involving the N H protons bound to the carboxylate portion of complementary, paired calix[4]pyrrole. Upon
addition of [D,]methanol, the resonance at 6 = 11 vanishes as
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Keywords: anion binding
assembly
*
calixarenes
.
sapphyrin
*
self-
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Chrmi.stry,
duction
0570-0833196i3523-2784 $15.00+ .25;0
Angeu. Chem In/. Ed. E n d . 1996. 35. No.23124
COMMUNICATIONS
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Lynch, A Harriman. I. L Sessler, hid. 1992, 114, 5714-5722.
[I71 Due to its size and basicity. the pentapyrrolic core of sapphyrin is monoprotonated at neutral pH 1161.
1181 4.Baeyer. Ber. D/st/r. Chem. Gev. 1886, f9, 2184-2185.
[I91 P A. Gale. J. L Sessler. V. K d , V. LynchJ: Am. Chem. Soc. 1996, I f R , 51405141
[20] a) Crystallographic data for (C,,H,,N,O:)(CF,CO;).CH,OH.
Dark green
needles, triclinic. Pi. 2 = 2, ti =10.635(2), b =12.514(3), c =16.307(4) A,
Y = 82.88(2). /$ =77.98(2),
7 = 85.54(2)c,
V = 2103.3(9) A3, pCalcd
=
1.32 gcm-'. F(000) = 884. A total of 6565 reflections were measured, 5490
unique (R,,, = 0.152) on a Siemens P3 diffractometer using graphitemonochromatired Mo,, radiation (i
=.0 71073 A) The structure was refined
on F 2 to an R, = 0.250, with a conventional R = 0 131 (1567 reflections with
Fi)>4[u(4,)]). and a goodness of tit -1.192 for 523 refined parameters.
Geometry of the hydrogen-bonding interaction (distances [A], angles ["I):
N l - H l N . . - O l a . N . -02.827(13),H.. 01.959(13),N-H-~~0161.7(12),
K2- H 2 N . . - 0 t a . N . - 02.901(14). H ' 0 2.235(14)), N - H . .O 130.5(12);
N 3 - H 3 N . - 0 4 2 (related by 1 -x, 1 - J,, - z ) , N - " O 2.763113). H . - O
1.944(13). N - H . 0 150.5(12); N 4 - H 4 N . , 0 4 2 (related by 1 -x,
1 -J, -:),
N - - 0 2.X16(13), H ..O 1.945(13). N - H - . - O 160.4(12); NSH 5 N - 0 4 2 (related by I - - I ,
I-J,-z),
N - . . O 2810(14). H - . 0
1 357(14). N H . . .O 157.7(11). b) Crystallographic data (excluding structure
'
Aneun.
Chem. lnt. Ed. E n d 1996, 35, NO. 23/24
factors) for the structures reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary publication no.
CCDC-179.112. Copies of the data can be obtained free of charge on application to The Director, CCDC, 12 Union Road. Cambridge CB2 IEZ, UK (fax.
Int. code +(1223) 336-033; e-mail: teched@,chemcrys.cam.ac.uk)
[21] Crystallographic data for (C,,H,,N,O;)(C,,H,,N').?CH,Cl,. Colorless
needles were grown from CH,Cl,, triclinic, Pi, Z = 7. u = 12.682(2), b =
13.127(2), c = 17.871(2) A, Y = 99.913(9), fi = 90.527(9). 7 = 98.49(1)",
V = 2896.7(6) A', pealed ~ 1 . 1 gcm-3,
8
F(OO0) =1116. A total of 11364 reflections were measured, 10078 unique (R,,, = 0 044) on a Siemens P4 diffractometer using graphite-monochromatized Mo,, radiation ( i = 0 71073 A). The
structure was refined on F 2 to an R, = 0.220, with a conventional R = 0.084,
with a goodness of fit =1.031 for 661 refined parameters. Geometry of the
hydrogen-bonding interaction (distances [A], angles ["I): N I H I N . - 0 1 (related by 1 - x . 1 - y , 1 - 2 ) . N . . 0 2975(5), H . . - O 219(4), N - H - - . O
162(4);N2-H2N.-.Ol,N..-02.980(5),H.-.O2.18(5).NH.--0167(4);
N 3 - H 3 N - . - 0 1 , N . . O 2.950(5), H . - . O 2.14(4). N - H . - 0 163(4); N4H 4 N . . 0 1 , N . . - 0 2.916(5), H . . 0 2 . 0 9 ( 4 ) , N - H . . - O 176(4)[20b]
[22] The sapphyrin bisacid I c is insoluble in either pure chloroform (or
dichloromethane) or methanol, but is soluble in mixtures of these solvents.
[23] The signals of the 'H NMR spectra of sapphyrin methyl esters 1b and 1d are,
on the other hand, well resolved in these solvents
(241 These same linker ethylene signals in sapphyrin bisacid 1c were broadened to
such an extent that their initial shifts could not be determined accurately.
[25] The proton chemical shifts of the linker ethylene group i n the control methyl
ester 1b, recorded under conditions analogous to those of the fluoride titration,
were found to remain almost unchanged.
~
In Situ Observation of Transient Reaction
Phenomena Occurring on Zeolite Catalysts
with the Aid of Positron Emission Profiling
Rutger A. van Santen,* B. G. Anderson,
R. H. Cunningham, A. V. G. Mangnus,
Dr. L. J. van IJzendoorn, and M. J. A. de Voigt
Zeolites are widely used in the petroleum refining industry as
solid acid catalysts to convert hydrocarbons into gasoline products of high octane number by isomerization or by cracking
reactions.['' Stable operation at mild reaction conditions is
made possible by the addition of noble metals to acidic zeolites.
For example, after addition of platinum to the zeolite H-mordenite n-hexane isomerizes to its structural isomers at 240°C
rather than at 400 0C.[21The state of the platinum in the working
catalyst and the distribution profiles of the reactive surface intermediates are strongly dependent on pretreatment and reaction conditions. Thus in situ measurement is necessary.
Positron emission tomography (PET) is a noninvasive, in situ,
radiochemical imaging technique used in nuclear medicine to
monitor biomedical functions.[3. 41 This technique has recently
been applied to systems in engineering research by Bridgwater et
al.[5361to study mechanical mixing within a powder mixer. In
addition we have shown that this technique can be used to
provide information on the concentration distributions of reactants and products as a function of time and position along the
reactor bed during the CO oxidation under steady-state conditions.['. *I This information is essential for the development of
kinetic models describing the rates of elementary reaction steps.
[*I
Prof. Dr. R. A van Santen, Dr. B. G. Anderson, Dr. R. H. Cunningham
Department of Chemical Engineering and Chemistry
Schuit Institute of Catalysis
Eindhoven University of Technology
P. 0. Box 513, 5600 MB Eindhoven (The Netherlands)
Fax: Int. code + (40)245-5054
e-mail' tgtaba(dchem.tue. NL
Ir. A. V. G Mangnus, Dr. L J van IJzendoorn, Prof. Dr. M J. A de Voigt
Department of Technical Physics
Schuit Institute of Catalysis (The Netherlands)
VCH Verlugsgesellschaft mhH, 0-694St Weinheim, 1996
OS70-0833/96/3523-2785 $ 15 OO+ 2 5 0
2785
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