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Conformational Effects on the Redox Potentials of Tetraarylporphyrins Halogenated at the -Pyrrole Positions.

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ready expressed our view that prolonged contact at close distances holds the key to the reactivity of both enzymes and enzyme models.['0~2'1
Multicomponent clumps are being investigated as catalysts
for diverse organic reactions by using the same screening procedure that uncovered the fast amide hydroIysi~.[~l
There is an
amusing parallel here to biological evolution : The randomly
created clumps correspond to random mutations; our selecting
clumps with the fastest rates corresponds to natural selection of
the fittest: and (to push the analogy to its limits) the publishing
of our best clumps corresponds to the passing on of the most
advantageous traits to future generations.
E,xprrirnental Procedure
Amide 2 wassynthesi~edfollowing the reaction C,,H,,N(CH,),
+
BrCH,COOCH,
+
CI~H,,N(CH,),CH,COOCH,Br~= RCOOCH, 4 RCOOH + RCOBr +
RCONHPhNO, (puru isomer). After three recrystallizations amide 2 had a m.p. of
213 214 C ;the spectroscopic data ( ' H N M R , FAB-MS. I R ) and elemental analysis wei-e consistent with the given structure. Reactions were monitored at 390 nm by
using a Varian D M S 200 spectrophotometer with il cell chamber thermostated at
25.0&0.1 C . The solvent consisted 01'3% CH,CN in a n aqueous phosphate buffer.
+
Received: Jul) 28. 1993
Rmised. September 2. 1993 [Z6241 IE]
German version: lizgcii . C/iwii. 1994. 106. 329
[l] F. Monod. Sciericr 1977. 196. 1161
-dimethyldodecylamine. do[2] Typical clump components (hexadecanoate.
decanol. the copper complex of C,,H,,N(CH,)CH,CH,N(CH,),
etc ) were
combined in concentrations of <
M each. Details will be described when
the work is completed.
[3] M. L. Bender. J A m Chrni. Soc. 1957. 79. 12%.
[4] R. Kltiger. 1. Chin, WW
: . Choy. .I .4in C/irtn.So<. 1979. 101. 6976.
[5] J T. Groves. R. M. Dias, J A m Chcrii. Soc. 1979. 101. 1033.
(61 I. B. Blagoeva, A. 1. Kirby. J C/7wi~.So<.P d n i Pun$ 2 1985. 1017.
[7] J. Suh, M. J. Kim. N . J. Seong. J Org. Chrm. 1981, 46, 4354.
181 A. J. Kirby. R. S. McDonald, C . R. Smith.J Cltem. S o . P L T X I 7i.a/7.\.
~
2 1974,
1495.
[Y] J C . Eck. C. S. Mai-vel. O r ~ q i m.Sjnc/ie..ch. Co//Lwr. I+/. / I . Wiley. Neu I'ork.
1943. p. 374.
[lo] F. M. Mengei. M. Ladika. J A m . C/imi. S o r . 1988. f10.6794
[ l l ] A. J Kirby, A h . P / i ~ s Orx.
.
Chrm. 1980, /7. 183.
[I?] R. G. Shorenstein. C . S. Pratt. C . J. Hsu. T. E. Wagner. .L h 7 i . C / w n .Soc. 1968,
YO. 6199.
1131 C . Gitler. A. Ochoa-Solano. J h i . Chcmi. So<. 1968. PO. 5004.
[14] R A. Mos5. R. C. Nahas, S. Ramaswani. W. J. Sanders. T e t r a l i f i l , . ~Lr/r
~~
1975. 3379.
[15] I- M. Menger. M. Ladika. J Am. C'h(wr. Sol. 1987. f O Y . 3145.
1161 K . D Janda, D. Schloeder. S J. Benkovic. R. A. Lerner. S'rienw 1988. 241.
118X.
(171 E. W. Kaler, A. K. Murthy. B. E. RodrigueL. J. A. Zasadsinski. Scfcme 1989,
145. 1371: H. Fukuda. K. Kauata. H . Okuda. S L. Regen. J Am. Clirm Soc.
1990. / I ? . 1635.
1181 H. W. Hoyer. A. Marmo. M . Zoellner. .L Phi,.\. C/imi. 1961. 6.5. 1804
[19] See rcf.[l0] for a related intramolecular case in uhich amide cleawge can he
slowcr than hydrolysis of an anhydride.
[ZO] F. M. Menger. Acr.. Chrf,i. Xi,.$1993. 26, 206.
1211 For ;i review ofcatalysis in organic "systenii". see F. M . Menger, dirgeti. C / w n
1991. 103. 3104; Aii,?eti Cheni. l i i / . Ed Engl. 1991, 30, 1086
Conformational Effects on the Redox
Potentials of Tetraarylporphyrins Halogenated
at the P-Pyrrole Positions**
Philippe Ochsenbein, Khadija Ayougou, Dominique
Mandon, Jean Fischer, Raymond Weiss,* Rachel N.
Austin, Karupiah Jayaraj, Avram Gold, James Terner,
and Jack Fajer
Porphyrins with alkyl substituents in the p-positions of the
pyrroles are easier to oxidize and harder to reduce than porphyrins bearing phenyl substituents at the meso positions."]
Nickel(I1) and zinc(rr) derivatives of p-alkyl-substituted tetraphenylporphyrins, which are hybrids of these two major types,
adopt saddle conformations and are more easily oxidized than
the corresponding octaethyl- or tetraphenylporphyrins, in accord with the theoretically predicted destabilization of the n
system resulting from the saddle distortion.I2.31 In contrast,
tetraphenylporphyrins that are partially halogenated at the
pyrrole [&positions are easier to reduce and harder to oxidize
than the nonhalogenated parent ma~rocycle.[~]
To gain insights
into the relationship between the redox potentials of tetraarylporphyrins halogenated at the 8-positions of the pyrroles and
substituent-induced changes in macrocycle conformation, we
have investigated the electrochemical properties and crystal
structures of 5.1 0, I5,20-tetramesitylporphyrin l,l5I derivatives
2 and 3[61 halogenated at antipodal pyrrole p-positions
(7,8,17,18), and derivatives 4 and 517] halogenated at all /Ipyrrole positions (2,3,7.8.12.13,17,18). The observation that the
octahalogenated macrocycles are easier to oxidize than the te-
bMe
Me
l . X = H , Y=H
2: X= CI, Y = H
4: X = C I , Y = C I
5:X=Br,Y=Br
Me
' M e 6 Me y
[*] Prof. Dr. R. Weiss, P. Ochsenbein, K. A)ougou, Dr. D. Mandon.
Prof. Dr. J. Fischer. Dr. J Fajer"'
Laboratoire de Cristallochimie et de Chimie Structurale (UA 424)
Universite Louis Pasteur. Institut Le Be1
4, rue B. Pascal. F-67070 Strasbourg (France)
Telefax: Int. code + (33)88415363
R. K . Austin. Dr. K . Jayaraj. Prof. Dr. A. Gold
Department of En\ ironmental Science and Engineering
University of North Carolina
Chapel Hill. N C 77599-7400 (USA)
Prof. Dr. J Terner
Department of Chemistry, Virginia Commonwealth University
Richmond. VA 23284-2006 (USA)
[ '1 Perinanent address.
Department of Applied Science
Brookhaven National Laboratory, Upton. N Y 11 973 (USA)
[**I This work uils supported by the Centre National de la Recherche Scientifique
(UA-424). the U S Public Health Service (Grants ES03433 for A . G . and
GM34442 for J. T.), the U.S. Department of Energy (Contract DE-AC-0276CH00016 tor J. F.), and NATO (collaborative research grant for R. W. and
A. G.). 1. Fajcr thanks the Department of Chemistry of the Universite Louis
Pasteur de Strashourg Tor a visiting profescorship.
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trahalogenated derivatives is rationalized by the effects of distortion of the porphyrin framework.
The crystal structures of 2 and 3 have a center of symmetry
and hence at least Ci symmetry.['] As a consequence, they are
not saddle-shaped but show a slightly distorted chairlike conformation (Fig. 1 ) . The two opposite halogenated pyrrole rings are
tilted up and down with respect to the mean plane of the porphyrin framework and are also twisted around their median
lines, whereas the nonhalogenated rings are only twisted. Both
/)-carbon atoms of the halogenated pyrrole rings lie above or
below the porphyrin mean plane; their average displacements
are 0.03( 1 ) 8, in 2 and 0.1 05(6) 8,in 3. The b-carbon atoms of the
nonhalogenated rings have corresponding average displacements of 0.02(2) 8, in 2 and 0.050(6) 8, in 3. Difference electron
density maps of 3 and 'H N M R studies of 2 and 3 in CD,CI,
show that the two NH protons are located on the nonhalogenated pyrrole rings. in agreement with a previous study of p-tetrabroininated tetraarylporphyrins.[61
1
minimized in the tetrahalogenated macrocycles by increasing
the (X-C,) C,-C,-C,,, angle relative to the (H-C,) C,-C,,-C,,
complement. The mean values of these angles are 120.8(4)" and
113.9(4)' in 2 and 122.2(2)" and 112.4(2) in 3, respectively.
The smallest ruffling of the porphyrin ring occurs in 1, where
the average displacement of the C,, carbon atoms with respect to
the porphyrin mean plane is only 0.015(4) 8, (Fig.
The
tetrahalogenated tetramesitylporphyrins are slightly more ruffled; the meso-carbon atoms lie 0.04(1) 8,above (and below) the
porphyrin mean plane in 2 and 0.087(6) 8, in 3. Ruffling is most
pronounced in the octahalogenated porphyrins 4 and 5. where
the displacement of the meso-carbon atoms relative to the porphyrin mean plane is 0.322(5) 8, and 0.30(2) A, respectively.
The experimental one-electron redox potentials E,f;' and E,!::
were determined by cyclic voltammetry for 1-5 (Table 1 ). Substitution at the pyrrole /]-positions with electron-withdrawing
groups makes the porphyrins easier to reduce and harder to
oxidize than the parent tetramesitylporphyrin. The differences
in the reduction potentials AEf:: for 1/2. 1/3, 2/4, and 3/57 range
from $0.25 to +0.32 V. While the difference in the oxidation
potentials AE,':z for 112 and 1/3 are positive (though somewhat
smaller than the values of AE:;:), the AE;:' values are negative
for 2/4 ( - 0.10 V) and 3/5 ( - 0.13 V) indicating that the octahalogenated porphyrins 4 and 5 are easier to oxidize than the
tetrahalogenated derivatives 2 and 3. in spite of the additional
{)-halogen substituents.
2
Table I . Redox potentials determined by cyclic voltammetry [ a ] .
Porphyrin
1
3
Halogen
substituents
~
E'!;2
&fc:
AE:~:
- 1.41
2
4Ci
- 1 .I2
4
8 CI
I
3
-0.x5
- I .41
4 Br
- I .09
5
8 Br
-0.84
+0.29
+ 0.27
f0.32
+0.25
AE!,Z
+ 0.9 I
+ 1 IS
+ 1.os
+ 0.9 I
+ 1.12
+0.99
+0.?4
- 0 10
f0.21
-0 I?
E l ' inV;solventCH,CI,,clectrolyteNBu,PF,(0.1 molL-')vs.SC'E.sc;in r'lte
200 m V s - ' . T = 25 C .
[a]
4
Fig. 1. Edge-on views of :he skeleton5 of ie:raiiiesitylporphyrin I . thc antipodal
tetrasubstituted derivatives 2 and 3, and the octachloro derivative 4 (the i m x mesityl groups are omitted for clarity).
As in the crystal structure of 5,[71the macrocycle 4 lies on a
crystallographic fourfold inversion axis and hence has S, symmetry.[81Since the two N H groups preclude symmetry higher
than C,. two tautomeric forms must be disordered around the
S, axis. Porphyrin 4 is also clearly saddle-shaped;'*] alternate
pyrrole rings are tilted severely up or down relative to the porphyrin mean plane and are also twisted about their median lines
(Fig. 1 ) . The average displacement of the b-carbon atoms of one
pyrrole ring relative to the porphyrin mean plane is 0.905(5) 8,
in 4, compared to 0.95(2) 8, in 5.['] The mesityl rings are twisted
into the porphyrin mean plane to minimize unfavorable contacts with the /l-pyrrole substituents. The average dihedral angle
between the two planes is 58.1(1)" in 4 and 58.6(6)^ in 5. The
corresponding values of 83.6(3)' in 2 and 84.9(1)" in 3 are close
to the angle of 83.6(1). found in 1. Unfavorable contacts are
The one-electron redox potentials of porphyrins reflect the
energy levels of their HOMOs and LUMOS.'~'INDO calculations on tetraphenylporphyrins octaalkyl-substituted at the
pyrrole []-positions have shown that saddle distortions of the
macrocycle decrease the energy gap between the HOMOs and
LUMOs by raising the energy of the HOMOS.'^' Thus, /]-alkyl
substitution decreases EAL2. while E::: is almost unchanged.[31
The data in Table 1 shows that the electron-withdrawing P-halogen substituents stabilize the LUMOs and, to a slightly lesser
degree. the HOMOs. The negative values of AE!iz for 214 and
315 can be explained if the energy decrease in the HOMOs of 4
and 5 expected from substitution with additional electron-withdrawing halogens is offset by the saddle distortion. That the
saddle distortions observed in the solid state are maintained in
solution is evidenced by the strongly red-shifted Soret and Q
absorption bands of 4 and 5 and shifts of the vz marker bands
in the resonance Raman spectra of the molecules.[9. 'I
E.qxv+nmiul Procedure
1 w'a? prepared according to a published procedure [ 5 ] .Single crystals of I 7 CHCI,
w r i t obtained by slow diffusion of hexanc into a solution of the poi-phyrin in
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chloi-oforin Cryst:il data ( - 100 C, dni-k blue crystal of dimensions
0.30 x 0.30 x 0.22 inin) C&,,,N,CI,.
~VI= 1021.8. tetragonal. space group /1,.o.
( I =27.093(X).
,.=14.876(6).&. L'=1091Y4A3. Z = 8. e,,,L,,=1.246gcin-2.
i(C'uK,) = 1.5418 A , 4269 rcllectiony (3 i (i i
52 ) were collectcd: einpirical ahwrptioii coi-rections were applied. 2337 irefleetions aith / > 3 n ( / ) were used in the
i-clinemetits: number ofpar;iinctei-h 337. R = 0.064. R , = 0.089. G O F = 1.45. h i l
residual electron densit) = 0.11 r A i
2: 1 (100 mp) was treated with 5.4 cquic of ,\.'-chlorosucciniinide in hoiliiig 1.1.?.7tetriiclilOroethiine (30 inL) liir 60 h. The crude reaction product xiis ptirilied twicc
bq chromatograph) o n a S i 0 2 column. first elutiiip with tolueiie and then with
tolueiie.Iiex;ine ( I . 1). T h e producl wa\ r-ecrystalli/ed by slo\\i addition o1'ineth;inol
to .;elution o f t h e c o i n p o u n d i t i chloroform. 'ield: 5Y'Lb. U V ' V l S (CH,C12. 75 C ) :
; , , , , , \ ( I [iiiol-' Lciii 'I) = 426 (231). 522 (lc1.5). 598.5 ( 6 . 8 ) , 654.5 niii (8.0). Single
crystals o f 2 4CHCI, werc obtaincd by s k i s dil'fusion ol-inethanol i i i t o ii solution
o ft h e porphbrin in chloroform. Cr!stnl data ( - 100 C. red-purplecrqstal oldiinen\ionsll.15 x 0 10 x 0.32 nini) C ~ , ~ ~ H 5 a K , C.5/
I , ~=, .1398.4. triclinic. space group P i .
t i =1I.l82i31.
h = 12.07Xi3). c =13.501(4)
3 =74.57(2). /I A 67.59(2), ;' =
8 7 . 8 7 ( 2 ) . I'=162ll.XA". Z = l , gc,,,L,=1.433g~iii~'. ; ( M 0 , , ) = 0 . 7 1 0 7 A . 4175
reflections ( 2 < fI < 7 3 ) w r e collected: empirical absorption corrcclions were
applied. 1712 rellections with I > 3 n(1) w e r e used i n thc i-efinemeiit\. number of
p;ir;iinelcrr 266. R = 0.093. R, = 0 116. GOF = 2.02. final residual electron dciisit! = 031 e k '
A.
3 wa\ oht;iiiicd according to ii published procedure for tetraarylporph)riiis 161.
U V ' V l S (CH,CI,. 25 C ) :
( I . [ n i o l - ' Lcm-'1) = 430 (214). 525 5 (70.3). 004
( X 0).660 5 inn (9.0). Single crystals o f [ 3 . 7C12C12]were obtained hq blow diffusion
o l peiirane into solution o f the por-phyrin i n dtchloroinethane. Crystal data
( - 100 C . hlack crystal of diinenvoiis 0.13 x 0.20 x 0.38 miii): C,,HI,N,Bi-,CI,.
.Lf = 126X.5. monocliiiic. space group P1,,'ii. ii = 11.413(3). h = 17.X56(5).
I = 13.736(4)
/ j = 1 0 2 40(?) . V = 7731.1 A'.
Z = 2. Q
i i M o , , ) = 0.7107 A: 5189 reflections (7 i0 < 25 ) w'cre coll
sorption corrections were applte
reflections with / > 3 n ( / )weie used i i i the
i-eliiieinents: nuinber of parame
R = 0 052. R , = 0.075. G O F = I .58. final
residu;il electron density = 0.31
The Effect of Chiral Bilayers:
Wax Tubes Made of (5)-Nonacosan-10-ol**
Jurgen-Hinrich Fuhrhop,* Thomas Bedurke,
A i r a n Hahn, Siegfried Grund, Jiirgen Gatzmann,
and Markus Riederer
The CO,/O, gaseous exchange in pine needles and similar
lipophilic leaf structures occurs through stomata which are covered by a dense mesh of lipid tubes.[" These tubes have internal
diameters of 0.1 -0.5 pm and consist of hydrophobic wax with
an extremely high content of hydrocarbon unitsr2. The function
of these tubes is presumably to filter off suspended particles from
the air. which -if they have accumulated despite this-may be
washed off the smooth, hydrophobic surface by rain. Whereas
pinc needles from healthy trees keep their tube system intact for
six years. the tube system of diseased trees breaks down within
months.[41The stomata become blocked by the lipids of the
tubes. We are interested in whether the curvature of the tubes is
related to the chirality of their constituents.[s1
The main component of the lipid tubes that are pressed out
through the wax cuticle (Fig. 1 a) is the secondary alcohol nona-
A.
.
4 : The iinc \aIt of 1 (200 nip) wiis created n i t h 70 equi! o f ,~-ctilorosuccinirnidcin
rcllurinp teti-achloroethylene (200 inL) for 17 h. The crude product ~ i i purified
s
by
c l i r o i i i a t ~ i g r i i p ohn~ a SiO, column eluting with dicliloromethaiir 'liexane ( I : 1 ). The
complex \\as deinetalated bq stirring in 10 Yo v:v trifluoroxetic acid III
dichloromethans for 23 11. "icld: 34YO. Single crystals o f 4 2Cl1,OH \{ere obtained bq 4ow diffusion of 1ie'i:ine into a solution of (he porphyrin in
dichloroinethnne:ineth~iiiol.Crystal data ( - 100 C. block crystal of dimensiona
0.15 x 0.25 x 0.40 mm): C,,tt,,N,C1,02,
.&I = 1122.7. tefrapoii,il. \pace gi-oup
P 4 2 , ~ . 0 = 1 5 . U 1 1 ( 4 ) , c = 1 3 . 2 8 9 ( 3 ) A .I ' = 2 9 9 4 4 A ' . Z = 2 . p , , , . ,
=1.206pcm 3~
i ( M o , , ) = 0.7107 A , 4851 i-ellections ( 2 < 0 < 19 ) were collected: empirical a h aorption cot-rcctions were applied. 1257 reflections with I > 3 n ( / )\$ere used iii the
relineinents: number of parameters 172. R = 0.044. R , = 0.058. GOI- = 1 .I2. liiial
rrsiduitl electron density = 0.43 e k ' .
Received: August 26. 1993 [Z 6317 IE]
German verbion: 41igcii.. Chiwi. 1994. 106. 355
R. H. Felton in Tltr E o r p i i ~r.bi\. I d . 5 ( E d . : D. Dolphin). Academic Press. Ne"
York. 1978. p. 53.
K. M . Barkigia, L. Chdntranupong. K. M. Smith, J. Fajer. J .In1 C'hci~iSoc.
1988. //O. 7566.
K. M Barkigia. M. W Renner. L. R . Furenlid. C. J. Medliirth, K . M Smith.
J Fajer. .I. h i . Clirni. Soc. 1993. 115. 3627.
A . Giraudeau. H J. Cullot. V.Grosc. /nor.g Chor?. 1979. I K . 201
M . Kihn-Botulinski. R. Meunier h o r g . C h w . 1988. 27. 209.
M . J Crosdey. P L. Burn. S. S. < hew,. F. B. Cuttance, 1. A. Newsoiii../. Clrriii.
SOC. c'l~twi.C m i n i m 1991. 1564.
D . Mandon. P. Ochsenbein. J. Fischer, R . Weiss. K J>I)W:~J. R . N Austin. A .
Gold. P S. White. 0 . Brigaud. P. Rattioni. D. Mansuy. Inoi:i.. Ciicni. 1992. 31.
2044.
Further details of the crystal sti-ucture investigations iiiay be obtained from the
~achiiir~ji-matioiis7entruin
K a i Isriihe. D-76344 Egp~nstein-Leopoldsh~ifeii
1
( F R G ) . on quoting the depositor) number CSD-57734. the names of the iiiithors, :mi the lournal citiition.
U V , V I S (CH2CI2.25 C): 4 . i,,,,( i : [ i n o l ~ ' L c m ~ ' ]=l 453.5(211). 548.5(17).
592.5(11). 702.5 ntnil;); 5 . i,,,,,(i:[inol-'LciiiCl]) = 463(177). 559(14).
AOh(9). 717 n n i ( 7 ) .
Reionaiice Rdman spcctrnin (CH,CI,. 4067-A excitation. based o n polari7atioiistudies)V4 v 2 = 1 5 3 7 c m l . 5 : 1 ~ , = 1 5 1 3 c i n ~ ' .
350
microscopy images o f a ) MIX tube\ in their niituriil CIIYItubes made from natural nonacosan-10-ol.
nthcsiied iS.R)-nonncos;in-lO-ol. and d) tube\ innde from
ti-10-ol. The tubes in Fig. 1 b. d a n d the platelets i n Fig. I c
were obtained from chloroforiii.
1
ronmcnt
in
pine needle itoinat;i. b)
[*IP r o f Dr. JLH. Fuhrhop. 7 Bedurke. A. H a h n
liiatitiit fill- Organische Cheinie dcr Freien Universitdt
T;ikustr;ilSc -3. 0-14105 Berlin ( F R G )
?!-of. D r S Grund. J. Gatimann
Labor:itoriuin fur- Elektronenmikroskol,ie dcr Freieii Univei-sitlit Bet-lm urid
der Humholdr-Univcrsitat ( F R G )
Pi-of.Dr M . Riedei-er
Institut f u r ?hq\iologische Okologic der Universitht K a i s c r h u t e r n ( F R G )
I**]
This work s i i c suppoi-ted by the Rundesininisterium fur Forschung und Technolopie (Supramolecular chemistry pilot project). tlie Deutsche Forschungsgeineinschaft (SFB 312 directioixil meinbrane processes). the F N K der Freien
Uni\erairiit Bri 1111. and t l i r Fonds der Cheniixheii Iiidustrie. We thank Di- A .
Schafcr for N M R mcasnrements.
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potential, conformational, effect, redox, tetraarylporphyrins, halogenated, pyrroles, positional
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