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Desorption Ionization Mass Spectrometry of
Synthetic Porphyrins
Leon Kurlansik and Taffy J. Williams
Naval Medical Research Institute, Bethesda, Maryland 20814, USA
John M. Strong and Lawrence W. Anderson
National Cancer Institute, Laboratorv of Medicinal Chemistry and Pharmacology, Bethesda, MD 20814, USA
Joseph E. CampanalNaval Research Laboratory, Chemistry Division, Washington, DC 20375, USA
The desorption ionization mass spectra are reported for two classes of synthetic porphyrins-‘tailed’ derivatives of
deuteroporphyrin IX and meso-substituted derivatized tetraphenylporphines. The mass spectra were obtained by
three desorption ionization techniques-fast atom bombardment (FAB), desorption chemical ionization (DCI) and
‘in-beam’ or desorption electron ionization (DEI). The emphasis of this study is to determine the usefulness of the
three desorption ionization methods for the molecular weight and side-chain structure determinations of synthetic
porphyrins. The molecular parent ions and the major fragmentation pathways are discussed in detail. The DEI
method yielded the fewest mass spectra showing molecular parent ions from the compounds studied, whereas FAB
gave the most. The major fragmentation pathways were compound dependent and similar for all three ionization
methods; generally, those cleavages a and p to carbonyl groups predominated. The FAB spectra showed strong
molecular adduct ions in several spectra that could be attributed to an in situ coordination of iron-containing
porphyrins with the thio-containing liquid matrix molecules.
INTRODUCTION
The porphyrins are recognized as being of great importance in biological, biochemical, geological and
petrochemical systems. Investigators have augmented
the naturally occurring porphyrins by modifying the
periphery Gf the macrocyclic ring in various ways ranging from ‘tailed’ compounds’ to forming intricate ‘picket
fence’,’ ‘ ~ a p p e d ’ ,and
~ ‘ ~ t r a p p e d ’molecules.
~
As the
complexity of these macromolecules increases, the
difficulty of their structural analysis also increases due
to occluded solvents, polymer formation, insolubility,
dimerization, involatility and thermal lability. The structural characterization of synthetic porphyrins has
ranged from the use of multiple instrumental techniques
(NMR,UV, IR) complemented with chemical analyses
(elemental analysis, thin-layer chromatography (TLC),
degradation gas chromatography) to the use of only
N M R spectroscopy and field desorption (FD) mass
spectrometry, or IR and electron ionization (EI) mass
spectrometry. The FD mass spectrometric technique has
been used to provide molecular weight information on
labile and involatile systems as well as mixtures of
porphyrin~.~-~
The most striking feature of the EI mass spectra of
the naturally occurring porphyrins is the high abundance
of the molecular ion.6 However, this is not the case when
the porphyrin contains labile side-chain constituents’ or
the porphyrin is intractable. Another characteristic
feature of the EI mass spectra of porphyrins is the
separation of distinct ion groups from low mass up to
the molecular ion region.’ The highest m / z group contains the molecular ion and species resulting from sidet Author to whom correspondence should be addressed.
chain fragmentation. The intermediate m/ z region contains doubly charged analogs of species observed in the
highest m l z group, and below the m / z 200 region few
species are observed that can be related to the macrocyclic nucleus. This indicates that the macrocyclic
tetrapyrrolic ring acts as an inert support and allows
detailed studies of side-chain f r a g m e n t a t i ~ nThe
. ~ most
characteristic fragmentations in the high mass region
are due to @type and benzylic cleavage^.^-^
The novel desorption ionization techiques-fast atom
bombardment (FAB): the ‘in-beam’ techniquesdesorption chemical ionization (DCI),” and desorption
electron ionization ( DEI)107”have not been investigated
for porphyrin characterization. Fast atom bombardment mass spectrometry has shown promise in its ability
to yield significant analytical information from polar
and involatile sample species.’ The FAB mass spectra
of a variety of intractable and underivatized middle
molecules,Y~‘2-’4
including protein^'^,'^ and pep tide^,'^"^
have given both molecular weight and structural information. Positive and negative ion mass spectra of compounds similar to porphyrins have been reported,” and
FAB mass spectra of biologically significant molecules
above m / z 57OO2O and inorganic cluster ions beyond
m / z 250002’-23have been obtained. The major fragmentations resulting from FAB are similar to those
observed by chemical and electron i ~ n i z a t i o n , ’and
~
carbon-heteroatom (C-X) cleavages predominate for
certain classes of compounds.12
The DEI and DCI methods also have been shown to
yield informative mass spectra from nonvolatile and
thermally labile compounds. 1 0 ~ ” ~ 2 5 - 2 7 Mechanistically,
the ‘in-beam’, direct exposure or desorption method is
not dissimilar to the volatilization process that occurs
with conventional direct probes in which a capillary
CCC-0306-042X/ 84/00 1 1-0475 $03S O
@ Wiley Heyden Ltd, 1984
BIOMEDICAL MASS SPECTROMETRY, VOL. 11, NO. 9, 1984 475
L. KURLANSIK, T. J. WILLIAMS, J. M. STRONG, L. W. ANDERSON A N D J. E. CAMPANA
sample holder is placed just outside the ion source.28
However, the volatility or desorption enhancement and
the closeness of the sample to the source of ionization
allow production of intact protonated molecules prior
to competing decomposition processes.28 This method
has been shown to be invaluable for the study of many
nonvolatile and thermally labile compounds.
We have determined the applicability of three desorption ionization mass spectrometric methods for the
molecular weight and side-chain characterization of synthetic porphyrins. We compared the positive ion mass
spectra obtained by FAB, DCI and DEI on 12 selected
porphyrin compounds that are representative of a variety
of porphyrins. The compounds selected for the study
(Fig. 1) may be considered to fall into two general
groups. The first series of tailed compounds (Fig. 1,
compounds 1-6) are functional derivatives of
deuteroporphyrin IX that are modified by the addition
of various side-chains at one of the two carboxylic acid
peripherals. The second series of meso-substituted porphyrins, compounds 7-12, are of the general class
tetraphenylporphines. These latter compounds have
been modified within the periphery of the nucleus so
that all additions are perpendicular to the plane of the
pyrrolic ring structure. Compound 12 is an exception to
this series ; the meso substituent is N- methylpyridinium
iodide to give an ionic, water-soluble compound. The
two series also contain zinc(I1) and iron(II1) chelates.
Table 1. Summary of the thioglycerol FAB mass spectrum
mlz
Species
(n = 1-3)
(n=1,2)
(n=1.2)
( n = 1-3)
(n=1,2)
( n = 1,2)
(n=1,2)
109, 217, 325
126. 234
91, 199
57, 165?, 273?
149, 1257
165?. 273?
73, 181
106
197?, 232?, 279?
dichloromethane, and an aliquot (containing 0.5-1 bg
of sample) was deposited on the desorption ('in-beam')
probe. The solvent was then evaporated under a stream
of dry nitrogen. The probe filament was linearly programmed from 20 to 400 mA at a rate of 7 mA s-' during
data acquisition. Methane (1 Torr) was used as the DCI
reactant gas, and the DEI mass spectra were obtained
with 70 eV electrons.
Relative ion abundances less than 5% of the base
peak are not reported in Tables 2-4.
RESULTS AND DISCUSSION
Molecular parent ions
~
~~
EXPERIMENTAL
The synthesis of the 12 subject compounds was accomplished by published method^^^^-*^-^' except for compound 4.3'The purity of the compounds was verified by
NMR, IR and UV spectroscopy in addition to the three
mass spectrometric methods.
The FAB spectra were obtained on VG Analytical
ZAB-HF and ZAB-2F double-focusing mass spectrometers (Manchester, UK) fitted with Ion Tech saddle
field guns (Teddington, UK); xenon was used as the
fast atom beam. A resolving power greater than 1000
was used for all studies, and spectra were recorded
oscillographically.
Thioglycerol
(3-mercapto- 1,2propanediol, Aldrich) was used as the FAB liquid matrix
for all samples; in one separate experiment (vide infru)
dithioglycerol ( 1,2-dimercapt0-3-propanol, Aldrich)
was used. The porphyrins studied were not soluble in
glycerol. Porphyrin samples were dissolved in the liquid
matrix, and a 1-2 ~1 aliquot was loaded on the FAB
probe. Additional instrumental details have been published e l s e ~ h e r e . ~ 'The
- ~ ~thioglycerol
,~~
gave rise to a
series of characteristic matrix ions (Table 1) analogous
to those observed from glycerol,33and a few unidentified
ion signals were observed. After a few minutes, a
m /z 106 ion appeared in high abundance in the thioglycerol FAB mass spectrum, presumably from bombardment-induced (radiation) damage of the thioglycerol.
The importance of the m/z 106 ion in these studies will
be discussed (vide infru).
The DCI and DEI mass spectra were obtained
on a Ribermag Model 210-10-C (Houston, Texas) quadrupole gas chromatographic/mass spectrometric/computer system. The samples were dissolved in
476
BIOMEDICAL MASS SPECTROMETRY, VOL. 11, NO. 9, 1984
Tables 2, 3 and 4 summarize the major ions and their
abundances observed in the highest mass regions of the
mass spectra obtained by DEI, DCI and FAB. Seven of
the 12 compounds studied by DEI gave molecular parent
Table 2. Summary of the DEI mass spectra of synthetic
porphyrins
Compound
no
2
572
685
3
675
4
962
5
737
6
729
7
a
9
674
736
1010
10
1064
11
12
1036
1 186(678)
1
a
Molecular
weight
Numbers refer to Fig. 1.
Relative to base peak.
m i r ( % relative abundance)b
470(65), 456(100), 442155). 428(15)
685(100), 625(8), 618(25), 592(10),
519(18), 459(12), 446(28), 431(10)
538(44), 523(53), 508(32), 465(88),
450(49), 432(53), 416(35), 408(100)
501(18), 487(22), 476(51), 462(100),
448(95), 434(40), 417(15)
600(56), 585(46), 569(14), 540(12),
527(72), 512(14), 469(29), 455(100),
439(32)
743(65), 709(11), 683(32), 665(60),
653(50). 592(100), 577(10), 559(19),
546(10), 534(19), 520(91), 506(11),
461(18), 459(23), 446(78), 431(21)
674( loo), 582( 10)
736(100), 844119). 554(15)
1011(100), 954(38). 926(28), 870(15),
786(8)
1065(38), 1009(53), 981 (100). 923(26),
897(46)
1037(100)
618( loo), 540( 14), 461 (10)
SYNTHETIC PORPHYRINS
COMPOUND
NO.
I
2
Mol.wt
EMPIRICAL
FORMULA
572
C3&IZ8O4N4Zn
685
C37H3903N7Fe
72 9
C 38 H 3905
N, Fe
674
C44H34 N8
H
736
C44H32N8Zn
C-C(CH3)3
1010
C64H66Ne04
1064
C64H64N8 04Fe
3
4
HO-CH
c=o
I
R I
R
COMPOUNDS
H
5
1-6
OCH3
6
Fe(LU)
OCH3
N -H
C-CH2Col
H '
c=o
NH
I
H,H
Zn
H
(II)
H,H
I1
OCH3
0
10
Fe ( I l l )
C.C(CH3)3
I1
0
COMPOUNDS
7- 10
( I-)4
12
Figure 1. Selected synthetic porphyrins studied by desorption ionization mass spectrometry. The first series, compounds 1-6, are functional
derivatives of deuteroporphyrin IX. The second series, compounds 7-12, are meso-substituted pseudo-tetraphenylporphines. 1 Zinc
deuteroporphyrin IX dicarboxylic acid; 2 iron deuteroporphyrin IX 6(7)-methyl ester (3)-imidazole propylamide; 3 Deuteroporphyrin IX
6(7)-methyl ester 7(6)-(histidine methyl ester); 4 iron deuteroporphyrin IX 6(7)-methyl ester 7-maltobionamide; 5 zinc deuteroporphyrin
IX 6(7)-methyl ester 7(6)-(histidine methyl ester); 6 iron deuteroporphyrin IX 6(7)-methyl ester 7(6)-(histidinemethyl ester); 7 meso-tetra(oaminopheny1)porphyrin; 8 zinc mesatetra( o-aminopheny1)porphyrin;9 meso-tetra (a,a,a,a-o-pivalamidopheny1)porphyrin; 10 iron mesotetra (a.a.a.ol-o-pivalaminopheny1)porphyrin; 11 capped porphyrin (Ref. 3); 12 tetra( N-methylpyridinium iodide)porphyrin.
BIOMEDICAL MASS SPECTROMETRY, VOL. 11. NO. 9, 1984 477
L. KURLANSIK, T. J. WILLIAMS, J. M. STRONG, L. W. ANDERSON A N D J. E. CAMPANA
Table 3. Summary of the DCI mass spectra of synthetic
porphyrins
Compound
no.a
1
572
2
685
3
675
4
962
5
737
6
729
7
674
736
1010
1064
a
9
10
11
12
a
Molecular
weight
Table 4. Summary of the FAB mass spectra of synthetic
porphyrins
Compound
no.=
m l z (% relative abundance)b
572(100). 554(6),528(5),513(33),454(25),
439(8)
685(100),671(5),627(5),603(5),519(7).
459(10),446(17),431(4)
704(9),690(23),676(17),631(10),612(18),
597120).552(16), 539(59),524(100),
510(30),492(12),480(14),466(38),
452(28),434(10),402(14)
490(12),476(57),462(83),448(100).
434(66),420(25)
751(22),737(10), 696(12). 673(24).
659(17),600(62),586(80),572(25),
542(18),527(74),514(32),495(10),
467138). 453(loo),439(29),423(10)
743(88),729(54),709(10),683(13),
665(37),651(25),592(44),578(63),
534(10),519(loo),505(27),487(13),
474(14),459(30),446(100),430(30),
416(8)
675(100)
738(100)
101 l(100).954(24),926(11)
1082(20),1065(41), 1031 (1 8), 101O( 100).
981 (76).926(22),897(33)
038(100)
1
2
3
4
5
6
7
1036
1186(678) No spectrum obtained
8
9
Numbers refer to Fig. 1.
Relative to base peak.
ions. Three molecular ion [MI” species (compounds 2,
7 and S), three protonated molecules [M+H]+ (compounds 9-11) and one [M +CH$ species (compound
6) probably formed by intermolecular transmethylation’
were observed. Protonated molecules in mass spectra
produced by the ‘in-beam’ EI method have been
reported.34
The DCI method on the subject compounds resulted
in molecular parent ions from 10 of the 12 compounds.
Four of the compounds (1,2,5 and 6) yielded molecular
ions [MI+’,four compounds (3,7,9 and 10) gave protonated molecules and two compounds (8 and 11) produced
[M +2H]+ species. The observation of abundant [M +
2H]’ to [M +4H]+ species has been reported for the EI
mass spectra of porphyrins and is generally thought to
occur by intermolecular h y d r ~ g e n a t i o n .Compound
~.~
3
yielded molecular parent ions resulting from ethyl and
methyl ion attachment, and 5 and 6 gave a [M +CH,]+
species. These three compounds (3, 5 and 6) show
methylene ion attachment whereas the other three compounds (1,2 and 4) in the first series do not. The common
functionality to the three compounds showing methyl
ion attachment is the methyl ester containing side-chain
of the R’ group. Considerable alkyl ion attachment has
been reported in the chemical ionization mass spectra
of ester^.^^,^^
Molecular parent ions were observed in the FAB mass
spectra of all 12 compounds. Compounds 2 and 4 yielded
molecular ions [MI+., compounds 1,3,5-10 and 12 gave
protonated molecules and the [M +3H]+ species was
observed for compound 11. Compound 12, the tetra(N478 BIOMEDICAL MASS SPECTROMETRY, VOL. 11, NO. 9, 1984
10
11
12
a
Molecular
weight
m l 2 (% relative
572
573(100),530(17),513(37),501(23),
488(28).471 (24).455(37),441 (34).
431(39).413(42),409(35)
685
791(9). 721(22),685(100),519(56),
505(14),487(8),474(12),459(30),446(42),
433(27),419(17),400(84)
675
827(44),813(73),690(29),676(81),
616(27).602(15),590(18),479(36),
465(41),433(51),420(63),405(100)
962
1284(12).1236(8),1 1 68(48).1 1 30(26),
1068(18), 985(15),975(16),962(85).
800(55),779(65),703(42),671 (21).
621(12),591(11),564(100),551(12),
533(9),520(23),506(7),499(5).456(12),
442(28),427(8)
737
752(7),738(100),724(5),679(5),600(5),
581(7),569(8),541(15),527(51),513(15),
495(29). 481 (20),467(44),456(52),
441(39),427(17),419(\6)
836(4),792(6),765(6),730(100),716(8),
729
670(8).532(7).519(40),506(9).487(15).
474(15),459(25),446(48),433(23),
419(1 1 )
674
837(24),823(94),779(27),709(25),
701(24).687(26),675(100),584(23)
774(57),765(54),751(100),737(79),
736
722(56),645184)
1010
1129(23),1036(33), 1026(40),1011(100),
997(21). 954(21),939(16),927(30)
1081(12),1065(79),1008(83),980(100)
1064
1036
1039(100)
1186(678) 805(24),691(14),679(100),663(34),
647(21 ), 633(36)
Numbers refer to Fig. 1
Relative to base peak.
methylpyridinium iodide)porphyrin salt (M4+I;;
mol. wt 1 186), yielded the molecular parent ions
[M4+I-+2e-](m/z 805) and [M4++4e- +HI ( m / z 679).
Additionally, nine of the compounds (2-10) gave various
molecular parent ions with m / z values above the
molecular ion or protonated molecule. Five of the compounds (2,4,6,7 and 9) gave ions that presently cannot
be related to the parent molecule. Although [M + Na]’
and [M +K]’ adduct ions are commonly observed in
FAB studies:.” only the FAB mass spectrum from compound 4 gave an observable ion signal ( m /z 985) corresponding to the [M + Na]+ species. Compound 8 gave an
ion signal at [M +38]+, which might be due to a [M - H +
K]+ species. Methyl ion attachment was observed with
3 and 5 as in the DCI spectra of these two compounds
and also with compound 8.
Compound 3, gave an ion at m/z 813 ([813 +CH,]
was also observed) that has been attributed to the
homologous diamide. Mechanistically, this species is
thought to form by the recombination or intermolecular
transposition of the R’ moiety to form the diamide
species within the FAB liquid matrix s ~ l u t i o n . ~ ’
The FAB mass spectra of 2, 4 and 6 gave ion signals
corresponding to [M + 106]+. Because these three porphyrins contain Fe(II1) and two of them have a sidechain or ‘tail’ with an imidazole terminus, the origin of
SYNTHETIC PORPHYRINS
this molecular parent ion can be postulated. Such porphyrin compounds are known to form a hexacoordinate
species with the imidazole nitrogen in the basal position
of the iron chelate,’ and the addition of sulfhydryl
groups to such compounds also has been e~tablished.~’
Therefore, the sulfhydryl group of the thioglycerol
matrix molecules resulting from radiation damage
( m / z 106, vide supra) attaches in situ to the apical position of the central metal, completing hexacoordination.
This postulate was further investigated with compound
6 using dithioglycerol (mol. wt 124) as the liquid matrix,
and a [M + 122]+ species was observed. While this latter
observation supports our postulate of a hexacoordinate
porphyrin species with the matrix species it leaves
some question as to the exact origin of the ligands (mol.
wt 106 from monothioglycerol and mol. wt 122 from
dithioglycerol). The ligand moiety may arise through a
free-radical mechanism in the matrix as postulated for
glycerol33or by dehydrogenation of the matrix molecule
during the chelation reaction. This postulate of coordination can be differentiated from attachment reactions
commonly observed with glycerol because the FAB mass
spectra of compounds 1 , 3 and 5, which do not contain
iron, do not show the [M+106]+ species. The ironcontaining picket-fence porphyrin, 10, did not give the
[M + 1061’ species, presumably due to steric hindrance
of the t-butyl ‘pickets’ and/or their inability to coordinate with the iron unlike the imidazole moiety. Several
studies have reported in situ reactions in the liquid FAB
matrix, including transpositions of side-chain moieties
(vide supra),32acetylation3’ and m e t h ~ l a t i o derivatizn~~
ation reactions.
Fragmentation
Deuteroporphyrin IX derivatives. This series of porphyrins
(compounds 1-6) is the ‘tailed’ functional derivatives
of deuteroporphyrin IX. The first and simplest of the
compounds, Zn deuteroporphyrin IX dicarboxylic acid,
gives a molecular parent ion with both DCI and FAB.
The DCI and FAB techniques give fragment ions due
to a-and P-cleavage at one carbonyl group. The spectra
from DEI, DCI and FAB methods show strong fragmentation due to P-cleavage at both propionic acid
side-chains. Various combinations of a-, P- and ycleavages are also observed, although less abundant.
Compound 2, Fe( 111) deuteroporphyrin IX 6 ( 7 ) methyl ester (3)-imidazole propylamide, gave a
molecular ion by each ionization method. The DEI
method was the only one giving a fragment ion due to
loss of the imidazole terminus ( m / z 618 ) . Common fragmentations were observed due to P-carbonyl cleavage
of the R’ group followed by a-and P-carbonyl cleavages
at the methyl propionyl side-chain. Further side-chain
cleavages due to undifferentiated methylene losses”
were also observed. The FAB mass spectra yielded two
additional fragment ions due to y-cleavage of the R
group and a-cleavage of both side-chains.
Compounds 3, 5 and 6 form a pseudo-homologous
series. The DEI method did not give a molecular ion
from compounds 3 and 5. The DEI and DCI techniques
yielded ions from the three compounds corresponding
to the replacement of R’ with a methoxy group, i.e. an
impurity. However, this suspected impurity only
y
CH3
w
,--.
,!32
o=c
‘0
/
H
CH3
Figure 2. Fragmentation scheme for the imidazole tailed porphyrins.
Substituent R, is common to compounds 3,4 and 6, and substituent
R2 is integral to compound 2.
appeared in minor abundance in the FAB spectrum of
compound 5, indicating that this species might originate
by a surface reaction on the ‘in-beam’ probe tip. Generally, loss of the R’ group, amide cleavage within the
R’ group, and a-,P- and y-carbonyl cleavage of the R
group were observed. Similarly, a-,P- and y-cleavages
of the methyl propionyl side-chain were also observed
following the cleavages of the R group. The FAB mass
spectra tended to be structurally more informative in
that a-cleavage within the R’ group was observed prior
to the loss of the R’ group, and a-cleavage of both R
and R’ was observed as well as P-cleavage of the R’
group with methoxy loss from the R group.
Figure 2 summarizes some of the common fragmentations of compounds 2, 3, 5 and 6. A series of fragment
ions is observed due to cleavages about the carbonyl
group on the side-chains R,, R2,and the common methyl
propionyl side-chain of the porphyrins. The fragmentation sequence for 2 is p-carbonyl cleavage at (a) in R2
followed by P-cleavage at (b). Generally, compounds 5
and 6 fragment preferentially by p-cleavage (based on
ion abundance) at (a) in Rl followed by p-cleavage at
(b). Additionally, the FAB spectra of compounds 3, 5
and 6 show an initial a-cleavage at (a’) in Rl. Compound
3, which contains no metal, appears to fragment first by
P-cleavage (a) in Rl followed by a-cleavage of the
methyl propionyl group, because no ion appears due to
the loss of the two moieties that would result from two
@cleavages.
The similarity in the fragmentation of compounds 3,
5 and 6, which have the same organic structure but
different metals, supports the observation that the mass
spectra of metalloporphyrins are similar to the mass
spectra of the parent porphyrin.6
Compound 4 yields a molecular ion only by the FAB
ionization process. It is evident by the comparison of 4
with the other compounds in the first series that the
macrocyclic nuclei and the metal (Fe) are the same as
others (compounds 2 and 6) that gave molecular parent
ions. One may conclude that the labile maltosecontaining tail results in significant fragmentation
and/or degradation of the molecule. The DEI and DCI
mass spectra are the least informative because no
molecular ion is observed, and the major fragmentations
are due to loss of the R group followed by a- and
P-cleavages of the methyl propionyl group and further
methylene losses. The FAB mass spectra show loss of
the alicyclic ring followed by successive cleavage of the
BIOMEDICAL MASS SPECTROMETRY,VOL. 11, NO. 9, 1984 479
L. KURLANSIK, T. J. WILLIAMS, J. M. STRONG, L. W. ANDERSON A N D J. E. CAMPANA
two amide functions within the R‘ group. Finally, the
FAB spectrum shows P-cleavage of the carbonyl nearest
the macrocycle followed by a-cleavage of the methyl
propionyl group.
Abundant series of doubly charged ions were not
observed as reported by other investigators using EI
mass spectrometry? The DEI spectra of compounds 1,
5 and 6 and the DCI spectrum of 1 displayed doubly
charged ions. The doubly charged species recorded corresponded to major fragment ions having side-chains
no greater than one methylene group attached to the
macrocyclic nucleus.
Mesosubstituted tetraphenylporphinederivatives. Compounds
7 and 8 and the ‘picket-fence’ porphyrins (9 and 10)
form a pseudo-homologous series. These four compounds all yielded molecular parent ions by each ionization method.
The DCI method did not give any fragment ions
resulting from loss of meso substituents from compounds 7 and 8. Benzylic cleavage resulting in the loss
of one or two anilino groups was observed with DEI
and FAB mass spectrometry.
The ‘picket-fence’ porphyrins (9 and 10) generally
gave mass spectra with high abundances of fragment
ions due to loss of one t-butyl group [M-(t-butyl)]+
and cleavage of the amide bond (loss of the R group)
[M - COC(CH3),]’. Additionally, the FAB spectrum of
compound 9 shows abundant [MH - CH,]+ and [M ( t-butyl) - CH,]+ species. The three ionization methods
give abundant fragment ions from compound 10 due to
amide cleavage (loss of R) and additional loss of a
t-butyl group [M - R- C(CH,),]+. This latter compound
also gives the [M -2R]+ fragment ion by DCI and DEI.
The DEI spectrum of 9 shows an ion signal m/z786
that may be the result of a-cleavage and the reduction
of all four R groups.
The capped porphyrin (11) does not show any fragmentation. Molecular parent ions [M +HI+ (DEI), [M +
2H]’ (DCI) and [M+3H]+ (FAB) are observed; the
latter two species are probably due to intermolecular
h y d r~ g e n a t i o n . ~ ’~
The tetraquaternary ammonium salt (12), did not give
a molecular ion of the intact salt (mol. wt 1186) by any
of the methods.
The FAB mass spectrum was the most informative
yielding a m / z 805 parent molecular ion species that
corresponds to [M4+I- +2e-] and a species at m / z 679
that corresponds to [M4++4e- + HI+. Successive loss of
methyl moieties from the latter species is also observed.
The DEI spectrum shows a species at m/z618 that
results from the reduction of the quaternary ammonium
benzenoid moiety to the pyridinyl group. This N-dealkylation is similar to that observed for internally N-alkylated porphyrins.8 Two consecutive benzyl-type
cleavages of these pyridinyl groups are observed in the
DEI mass spectrum. The DCI method did not yield a
mass spectrum of this compound.
The loss of moieties from the meso position has been
reported to be a dominant EI fragmentation pathway
for meso-substituted porphyrins.’ However, the ‘picketfence’ porphyrins (9 and 10) and the ‘capped’ porphyrin
(11) do not show this type of fragmentation. This
observation appears to suggest that conjugation of the
pyrrolic ring with the benzenoid moieties at the meso
480 BIOMEDICAL MASS SPECTROMETRY, VOL. 11, NO. 9, 1984
position is further enhanced by the addition of the
structures above the plane of the ring, yielding a species
stable against fragmentation at the internal energies
imparted by the ionization techniques.
There were no doubly charged species observed from
the second series of compounds.
SUMMARY AND CONCLUSIONS
The desorption ionization mass spectrometric techniques-DEI, DCI and FAB-can be of significant value
for the characterization of synthetic porphyrins.
Molecular parent ions were obtained for all 12 subject
compounds by FAB while DEI only yielded molecular
weight information on seven compounds. The major
fragmentation pathways observed in the desorption
ionization mass spectra were remarkably similar. Bond
cleavage a and P to carbonyl groups predominated for
the ‘tailed’ derivatives of deuteroporphyrin IX (compounds 1-6). The rneso-substituted tetraphenylporphine
derivatives (compounds 7 , 8 and 12) generally give benzylic-type cleavages of the meso substituents. The
‘picket-fence’ derivatives (compounds 9 and 10) of this
latter class did not show benzylic-type loss of the meso
substituents ;however, fragmentation of the ‘pickets’ was
observed. The ‘capped’ porphyrin (compound 11) did
not yield fragment ions. The increased stability of these
‘picket-fence’ and ‘capped’ porphyrins against fragmentation may be due to extended conjugation of the
modified porphyrin.
Generally, more structural information was obtained
through FAB on the first series of compounds, and FAB
and DEI gave about an equal number of structurally
significant fragment ions on the second series.
Although, FAB mass spectrometry gave molecular
weight information for each of the 12 compounds, other
abundant molecular adduct ions were observed in the
mass spectra of many of the compounds. A molecular
parent ion is observed for the iron-containing compounds 2, 4 and 6 at [M+106]+ that is postulated to
occur via the hexacoordination of the Fe( 111) chelate
with the imidazole tail of the compounds and the thioglycerol liquid matrix containing the reactive sulfhydryl
group. Other unidentified adduct ion species could complicate molecular weight determination; for example,
compound 4 (mol. wt 962) gives eight abundant
molecular parent ions-[MI+‘ (85%), [M + 13]+ (l6%),
[M+Na]+ (15%), [M+106]+ (18%) and [M+168]+?
(26%), [M +206]+? (48%), [M +274]+? (So/,) and [M +
322]+? (12%) of which the four highest mass species
have not been associated with the parent molecule.
Each ionization technique yields mass spectra that
contain some analytical information for the structural
characterization of the subject compounds. No one technique can be relied on to provide unambiguous
molecular weight and structural information. In fact,
additional techniques, such as FD mass spectrometry
for molecular weight determination of unknowns, may
be required.
Acknowledgements
The assistance of Brian N. Green of V. G. Analytical Ltd in obtaining
independent FAB mass spectra on some of the compounds is greatly
appreciated.
SYNTHETIC PORPHYRINS
A portion of this research was supported by the Naval Medical
Research and Development Command Research Work Unit No.
MR0412001.0435. T h e opinions and assertions contained herein are
the private ones of the authors and are not to be construed as official
or as reflecting the views of the Department of the Navy or the Naval
service at large.
REFERENCES
1. C. E. Castro, Bio-Inorganic Chem. 4, 45 (1974).
2. J. P. Collman, R. R. Gagne, C. A. Reed, T. R. Halvert. G. Lang
and W. T. Robinson, J. Am. Chem. SOC.97, 1427 (1975).
3. J. Almog, J. E. Baldwin, R. L. Dyer and M. Peters, J. Am. Chem.
SOC.97, 226 (1975).
4. J. E. Baldwin, M. J. Crossley, T. Klose, E. A. O'Rear 111 and M.
J. Peters, Tetrahedron 38, 27 (1982).
5. K. M. Smith, Porphyrins and Metalloporphyrins, p. 381. Elsevier,
New York (1975).
6. A. H. Jackson, Phil. Trans. Roy. SOC.London A293, 21 (1979).
7. H. Budzikiewicz, The Porphyrins, Vol. II, pp. 395-461. Academic
Press, New York (1978).
8. A. G. Smith and P. 8. Farmer, Biomed. Mass Spectrom. 9, 111
(1982).
9. M. Barber, R. S.Bordoli, G. J. Elliott, R. D. Sedgwick and A. N.
Tyler, Anal. Chem. 54, 645A (1982).
10. R. J. Cotter, Anal. Chem. 52. 1589A (1980).
11. M. Ohashi and N. Nakayama, Org. Mass Spectrom. 13. 642
(1978).
12. K. L. Rinehart, Science 218, 254 (1982).
13. C. Fenselau, R. Cotter, G. Hansen, T. Chen and D. Heller, J.
Chromatogr. 218, 21 (1981).
14. C. Fenselau, Anal. Chem. 54, 105A (1982).
15. K. Biemann, Koehshu-Tyo Masu Kenkyukai 6,21 (1981).
16. H. R. Morris, A. Dell, A. T. Etienne, M. Judkins, R. A. McDowell,
M. Panico and G. W. Taylor, Pure Appl. Chem. 54,267 (1982).
17. D. H. Williams, C. V. Bradley, S. Santikarn and G. Bojesen,
Biochem. J. 201, 105 (1982).
18. A. Dell and H. R. Morris, Biochem. Biophys. Res. Commun. 106,
1456 (1982).
19. M.Barber, R. S. Bordoli. R. D. Sedgwick and A. N. Tyler, Biomed.
Mass Spectrom. 8, 492 (1981).
20. M. Barber, R. S. Bordoli, G. J. Elliott, R. D. Sedgwick, A. N. Tyler
and B. N. Green, J. Chem. SOC., Chem. Commun. 936 (1982).
21. J. E. Campana, R. J. Colton. J. R. Wyatt, R. H. Bateman and B.
N. Green, Appl. Spectros. 38,430 (1984).
22. B. 1. Dunlap, J. E. Campana, 6. N. Green and R. H. Bateman, J
Vac. Sci. Techno/. A 1, 432 (1983).
23. J. E. Campana and B. I.Dunlap, lnt. J. Mass Spectrom. Ion Proc.
57, 103 (1984).
24. R. D. Grisby, S.E. Scheppele, Q. G. Grindstaff, G. P. Sturn, Jr,
L. C. E. Tayor, H. Tudge, C. Wakefield and S.Evans, Anal. Chem.
54, 1108 (1982).
25. M. A. Baldwin and F. A. McLafferty, Org. Mass Spectrom. 7,
1353 (1973).
26. A. Dell, D. H. Williams, H. R. Morris, G. A. Smith, J. Feeney and
G. C. K. Roberts, J. Am. Chem. SOC.97,2497 (1975).
27. G. Hansen and B. Munson, Anal. Chem. 50,1133 (1978).
28. R. J. Cotter and C. Fenselau, Biomed. Mass Spectrom. 6, 287
(1979).
29. M. Momenteau, M. Rougee and B. Laack, Eur. J. Biochem. 71,
63 (1976).
30. J. Alrnog, J. E. Baldwin, M. W. Crossley, J. D. Debernardis, R.
L. Dyer, J. R. Huff and M. J. Peters, Tetrahedron 37, 3589 (1981).
31. L. Kurlansik and T. J. Williams, in preparation.
32. L. Kurlansik, T. J. Williams, J. E. Campana, B. N. Green, L. W.
Anderson, and J. M. Strong, Biochem. Biophys. Res. Commun.
111,478 (1983).
33. F. H. Field, J. fhys. Chem. 86, 5115 (1982).
34. M. Ohashi, K. Tsujimoto and A. Yasuda, Chem. Lett. (Japan)
439 (1976).
35. M. S. B. Munson and F. H. Field, J. Am. Chem. SOC.88, 4337
(1966).
36. A. G. Harrison, Chemical lonization Mass Spectrometry, p. 11 1.
CRC Press, Boca Raton, Florida (1983).
37. C. K. Chang and D. Dolphin, J. Am. Chem. SOC.97,5948 (1975).
38. A. Dell, H. R. Morris, M. D. Levin and S. M. Hecht, Biochem.
Biophys. Res. Commun. 102, 730 (1981).
39. S. A. Martin, C. E. Costello and K. Biemann, Anal. Chem. 54,
2362 (1982).
Received 11 October 1983; accepted (revised) 13 February 1984
BIOMEDICAL MASS SPECTROMETRY, VOL. 11, NO. 9, 1984 481
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