Metal Complexes in Fossil Fuels - American Chemical Society

C h a p t e r 11 Metalloporphyrins in Lignite, Coal, and Calcite Raymond Bonnett, Philip J. Burke, and Franciszek Czechowski

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Department of Chemistry, Queen Mary College, Mile End Road, London E1 4NS, United Kingdom

The present understanding of work on porphyrins and metalloporphyrins in coals and lignites is summarised. New results are described on the isolation of individual porphyrins from the heme fraction of Colorado coal, from which two crystalline porphyrins have been obtained, and on the examination of iron and gallium porphyrins in the lithotypes (vitrain, durain) from a Polish sub bituminous coal (Janina). Gallium mesoporphyrin IX has been identified in a pink calcite from a hydrothermal region (Deutsch-Altenburg) in Austria.

The o c c u r r e n c e o f m e t a l s , i n c l u d i n g some r a t h e r r a r e m e t a l s , i n c o a l s i s w e l l known Ο ) · That some o f these m e t a l s a r e p r e s e n t i n p a r t a s t e t r a p y r r o l e complexes might, perhaps, have been i n f e r r e d from e a r l y o b s e r v a t i o n s on pigmented l e a f compressions i n brown c o a l ( M i d d l e Eocene) ( 2 ) , but i t was T r e i b s , i n h i s p i o n e e r i n g papers on o r g a n i c g e o c h e m i s t r y , who f i r s t r e p o r t e d i r o n and v a n a d y l p o r p h y r i n s i n c o a l s (3, _4). I n h i s s t u d i e s on f o s s i l f u e l s , T r e i b s c o n c e n t r a t e d on crude o i l and i t s r e l a t i v e s , p o s s i b l y because i n c e r t a i n o f t h e s e m a t e r i a l s the p o r p h y r i n c o n t e n t was l a r g e r and more amenable t o e x t r a c t i o n . Subsequent workers have f o l l o w e d T r e i b s i n t h i s p r e d i l e c t i o n a s i s i l l u s t r a t e d by t h e programme o f the p r e s e n t m e e t i n g : o f 14 o r so s c h e d u l e d papers on p o r p h y r i n s i n r e l a t i o n t o t h e g e o s p h e r e , t h i s i s the o n l y one t o have c o a l i n t h e t i t l e . The r e n a i s s a n c e o f t h e s u b j e c t o c c u r r e d i n t h e l a t e 1 9 7 0 s , w i t h the d i s c o v e r y o f g a l l i u m p o r p h y r i n s i n bituminous c o a l s ( 5 , _6). Subsequently i r o n p o r p h y r i n s , manganese p o r p h y r i n s (one example) and m e t a l - f r e e p o r p h y r i n s were a l s o d e t e c t e d ( 7 ) . Vanadyl and n i c k e l p o r p h y r i n s , which a r e commonly encountered i n c r u d e o i l and i t s r e l a t i v e s ( 8 ) , have not as y e t been found i n l i g n i t e and c o a l . Using e x t r a c t i o n p r o c e d u r e s which cause d e m e t a l l a t i o n , Palmer and coworkers (9) r e p o r t e d p o r p h y r i n s i n a number o f US humic c o a l s , and, more r e c e n t l y , Bonnett and Burke (10) demonstrated t h e o c c u r r e n c e o f i r o n p o r p h y r i n s i n seven such samples, i n some o f which m e t a l - f r e e and g a l l i u m p o r p h y r i n s were a l s o d e t e c t e d ( T a b l e I ) . f

0097-6156/87/0344-0173$06.00/0 © 1987 American Chemical Society

Filby and Branthaver; Metal Complexes in Fossil Fuels ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

174

M E T A L C O M P L E X E S IN FOSSIL FUELS

T a b l e I.

Coal C l a s s (Rank) Bituminous (HVA) Bituminous (HVC)


Bituminous (HVC) Sub-bituminous Lignite

Pennsylvania

Tetrapyrroles

i n C o a l s from the

3

Origin (Code) W. V i r g i n i a (PSOC-1001)

Age Penns y l v a n i a n

2H

Pennsylvanian

—

Cretaceous

—

Washington Eocene (PSOC-230A3) Montana Cretaceous (PSOC-833)

—

Indiana (PSOC-677) Colorado (PSOC-850)

State

—

U.S.A.

P o r p h y r i n s μg/g (duplicate) Ga Fe 0.07 0.35 (0.34) (0.09) 0.22 0.38 (0.50) (0.25) 0.20 12.9 (13.1) (0.18)

0.14 (0.15)

0.82 (0.89) 1.05 (1.03)

— —

University Collection

The but

c o a l p o r p h y r i n s t o r y i s s t i l l a t an e a r l y stage of development, i t i s u s e f u l t o summarise the main r e s u l t s so f a r .

1.

Metalloporphyrins (Ga, Fe, Mn) and m e t a l - f r e e p o r p h y r i n s and c h l o r i n s have been d e t e c t e d i n l i g n i t e s and b i t u m i n o u s c o a l s i n amounts from 0 t o 20 μg/g. The major group of t e t r a p y r r o l e s c o n s i s t s of a m i x t u r e of homologous p o l y a l k y l p o r p h y r i n s i n a p p r o x i m a t e l y the C 2 6 - C 3 2 range, the Qo and C32 members o f t e n b e i n g dominant (6, _7, 9>, 11). The C32 compound has not been d i s t i n g u i s h e d from e t i o p o r p h y r i n ( t y p e I I I isomer shown a t 1). The ^-H spectrum of the mixed homologues shows the p r e s e n c e o f u n s u b s t i t u t e d β-positions, presumably o c c u r r i n g i n lower homologues as a r e s u l t of a c i d c a t a l y s e d d e a l k y l a t i o n p r o c e s s e s (_7), o r a r i s i n g a t C-13 (as i n 2) from c h l o r o p h y l l p r e c u r s o r s .

2.

3.

4.

5.

Sub-bituminous c o a l s and, e s p e c i a l l y , l i g n i t e s o f t e n c o n t a i n e t i o p o r p h y r i n mono- and d i - c a r b o x y l i c a c i d s ( m e t a l l a t e d and metal-free). P u r i f i c a t i o n o f the i r o n e t i o p o r p h y r i n d i c a r b o x y l i c a c i d (Fe C32 diCOOH) f r a c t i o n from an A u s t r a l i a n l i g n i t e g i v e s a component (as the d i e s t e r ) which i s i d e n t i c a l w i t h m e s o p o r p h y r i n IX (3, as the d i e s t e r ) on the b a s i s of t i c and h p l c comparisons w i t h the a u t h e n t i c r e f e r e n c e samples, and on the b a s i s o f nmr s p e c t r o s c o p y (11, 12). The f o l l o w i n g g e n e r a l i s a t i o n s appear to h o l d . As c o a l rank i n c r e a s e s , l e s s p o r p h y r i n can be e x t r a c t e d ( a n t h r a c i t e s y i e l d o n l y t r a c e s of t e t r a p y r r o l e : _6, 7); carboxylic acid derivatives d e c r e a s e and v a n i s h ; the FeP/GaP r a t i o d e c r e a s e s (7); and t h e w e i g h t e d mean of the p o r p h y r i n m o l e c u l a r masses moves to lower v a l u e s (_9, 12). I t has been suggested t h a t the l a t t e r parameter has some m e r i t i n p r o v i d i n g an independent s c i e n t i f i c a l l y - b a s e d assessment of c o a l rank ( P o r p h y r i n Index of C o a l i f i c a t i o n : 12). The g e n e r a t i o n of lower homologues of a C 3 2 - p o r p h y r i n accords w i t h the g e o c h e m i c a l t r a n s f o r m a t i o n o f the c h l o r o p h y l l s : however, the o b s e r v a t i o n of m e s o p o r p h y r i n IX s u g g e s t s t h a t an a d d i t i o n a l pathway from m i c r o b i a l heme p r o t e i n s may a l s o be s i g n i f i c a n t ( 1 1 ) .


BONNETT ET A L .

Metalloporphyrins

in Lignite, Coal, and

Calcite


11.


175


176 Iron Porphyrins

i n Colorado

Coal


I t has r e c e n t l y been shown (10) t h a t a Cretaceous c o a l from C o l o r a d o i s p a r t i c u l a r l y r i c h i n i r o n p o r p h y r i n s ( c a . 12 μg/g, T a b l e I ) . T h i s c o a l was k i n d l y s u p p l i e d from the P e n n s y l v a n i a S t a t e U n i v e r s i t y C o l l e c t i o n through the c o u r t e s y o f P r o f e s s o r P.H. G i v e n , and some c h a r a c t e r i s t i c s of the c o a l are p r o v i d e d i n T a b l e I I . Petrog r a p h i c a l l y the c o a l i s o f i n t e r e s t i n b e i n g p a r t i c u l a r l y r i c h i n vitrinite.

Table Age:

II.

Characteristics

Cretaceous

Proximate a n a l y s i s Ash (d) 6.197o V o l a t i l e m a t t e r ( d a f ) 35.72%

Macérai c o m p o s i t i o n (dmmf, v o l . %) Vitrinite Fusinite 91.5 2.3 Source/Code

of C o l o r a d o Rank:

Coal

HVC

Ultimate analysis (daf) C 78.92% H 5.49% Ν 1.72% S 0.43%

Semi-fusinite 4.0

Micrinite 1.4

PSOC-850, Seam D

Mass s p e c t r o m e t r y has shown a range o f lower homologues o f etioheme ( a c c u r a t e m o l e c u l a r i o n measurements f o r the i r o n complexes o f C28, C 2 9 , C 3 0 > C 3 1 and C 3 2 p o r p h y r i n s ) : no p o r p h y r i n c a r b o x y l i c a c i d s were d e t e c t e d ( 1 0 ) . The s e p a r a t i o n of the components of t h i s homologous s e r i e s i s now i n hand, the aim b e i n g t o produce adequate q u a n t i t i e s o f c r y s t a l l i n e s i n g l e components f o r X-ray c r y s t a l l o g r a p h y . The s e p a r a t i o n i s a l e n g t h y p r o c e s s , and i s summarised i n F i g u r e 1. It has not yet proved p o s s i b l e to f r a c t i o n a t e i r o n p o r p h y r i n s by h i g h p r e s s u r e l i q u i d chromatography ( h p l c ) i n a s a t i s f a c t o r y manner, so the m i x t u r e i s d e m e t a l l a t e d . S t a r t i n g w i t h 4 Kg of the powdered c o a l , and f o l l o w i n g the u s u a l e x t r a c t i o n (_6, JJ_) w i t h 7% H2S0i+/Me0H and r e p e a t e d s e p a r a t i o n by t i c , an i r o n p o r p h y r i n c o n c e n t r a t e (36 mg) was o b t a i n e d . D e m e t a l l a t i o n gave a m i x t u r e o f p o r p h y r i n s the components of which c o u l d be a n a l y s e d by r e v e r s e phase h p l c , as shown i n F i g u r e 2. T h i s showed t h a t the m i x t u r e was v e r y complex, b u t , e n c o u r a g i n g l y , t h e r e were a p p a r e n t l y o n l y f o u r p r i n c i p a l components. For f u r t h e r s e p a r a t i o n , the m i x t u r e was m e t a l l a t e d w i t h z i n c , and t h e product was s u b j e c t e d to f u r t h e r stages of s e p a r a t i o n u s i n g semip r e p a r a t i v e hplc to give f o u r f r a c t i o n s , a l l four s t i l l being mixtures. These are l a b e l l e d A-D i n F i g u r e 1, where A i s the most p o l a r , and D i s the l e a s t s o . Repeated f r a c t i o n a t i o n u s i n g the same procedure showed t h a t A was o b t a i n e d i n o n l y minor amount, Β gave two components, B4B and B4C, which have not as yet been c r y s t a l l i s e d ; C gave C3B as a major c r y s t a l l i n e product (2.8 mg); w h i l e D gave D4C as a c r y s t a l l i n e


11.

BONNETT ET A L .

Metalloporphyrins


Calcite

177

Colorado c o a l (4 Kg)

1 I r o n porphyrins

(3 6 mg)


jdemetallate

M e t a l - f r e e porphyrins

a n a l y t i c a l hplc (Figure 2 )

insert zinc

Zinc(II)

porphyrins

[preparative hplc more polar i

less polar

semipreparative hplc

A1-A5 (minor)

B1-B6

ι

C1-C4

i

D1-D4

I

B4B

C3B

DMC

BMC

major

major

major not yet crystalline

2.8 mg

1.1 mg

crystals

crystals Zinc E t i o porphyrin I I I

F i g u r e 1. I s o l a t i o n o f m e t a l l o p o r p h y r i n s from C o l o r a d o c o a l (PSOC-850). Note t h a t t h e i r o n p o r p h y r i n s a r e d e m e t a l l a t e d and then c o n v e r t e d t o z i n c complexes t o a i d s e p a r a t i o n and identification.



178


F i g u r e 2. A n a l y t i c a l h p l c o f p o r p h y r i n s o b t a i n e d by d e m e t a l l a t i o n o f i r o n p o r p h y r i n f r a c t i o n from C o l o r a d o c o a l (see F i g u r e 1, Apex ODS, 3% MeOH/CH3CN).


11.

BONNETT ET A L .

MetaUoporphyrins


Calcite

179

product (1.4 mg). The l a t t e r compound i s indistinguishable chromatographically from etioporphyrin I I I : but X-ray and nOe effect results on this sample, and on f r a c t i o n C3B are awaited before secure conclusions can be drawn.


Porphyrins i n Relation to Pétrographie Components Up to the present time there has been no information on the v a r i a t i o n of porphyrin content i n r e l a t i o n to pétrographie composition. An experiment has now been carried out to examine this question, a subbituminous coal from Janina C o l l i e r y (East High S i l e s i a n Coal Basin, Poland) being selected. The separation into pétrographie constituent samples, v i t r a i n and durain, and the pétrographie analyses of these, was carried out with the help of Dr. H. Kidawa (Wroclaw): the r e s u l t s are shown i n Table I I I . While the composition of the "durain" lithotype does not precisely f i t the international d e f i n i t i o n f o r the durite microlithotype ( 95% i n e r t i n i t e + exinite, 5% v i t r i n i t e ) (13) i t does represent a considerable enrichment of i n e r t i n i t e and exinite over that of the raw coal (and a corresponding reduction i n vitrinite).

Table III.

Chemical and Pétrographie Analyses of Janina Raw i t s V i t r a i n and Durain Lithotypes Vitrain

Durain

5.76 40.6 77.0 4.9 1.30

3.30 36.5 74.7 4.6 0.92

7.69 38.0 77.6 4.5 1.47

61.1 14.7 1.7 21.5 0.9 0.1

96.9 0.9 0.2 1.8 0.1 0.1

17.2 28.1 9.8 44.6 0.2 0.1

Raw Chemical Analysis Ash (d) % V o l a t i l e matter (daf) % C (daf) % H (daf) % Ν (daf) % Maceral Composition Vitrinite Exinite Micrinite Fusinite Minerals Pyrite

Coal and

Coal

Janina coal contains appreciable amounts of both iron and gallium porphyrins: these were extracted and separated by t i c and estimated using the standard conventions which we have employed throughout ( v i z . a molecular weight of 600 i s assumed, and the molar extinction of the Soret band i s taken as 105,000 for iron porphyrins and as 400,000 for gallium porphyrins). The results are shown i n Table IV.


180


Table

IV.


Raw c o a l Vitrain Durain

M e t a l l o p o r p h y r i n Contents L i t h o t y p e s (\ig/g) FeP 5.83 1.03 0.24

of J a n i n a C o a l and i t s

GaP 0.67 0.96 0.27

The c o m p o s i t i o n s of the s i x m e t a l l o p o r p h y r i n s f r a c t i o n s were e s t i m a t e d by mass s p e c t r o m e t r y , w i t h the r e s u l t s shown i n F i g u r e 3. The p o r p h y r i n m i x t u r e comprises m a i n l y p o l y a l k y l p o r p h y r i n s i n the C 2 7 - C 3 2 range, w i t h a s m a l l amount o f m o n o c a r b o x y l i c a c i d ( l a b e l l e d C3 2 ) b e i n g d e t e c t e d i n the heme s p e c t r a . Three p r e l i m i n a r y c o n c l u s i o n s emerge from t h e s e r e s u l t s . F i r s t l y , f o r these t h r e e samples t h e r e i s a p a r a l l e l between the v i t r i n i t e c o n t e n t and the amount o f g a l l i u m p o r p h y r i n d e t e c t e d . Secondly, i r o n p o r p h y r i n seems to have been l o s t i n p r e p a r i n g the lithotypes. T h i s has l e d to the s u p p o s i t i o n t h a t i r o n p o r p h y r i n s a r e c o n c e n t r a t e d i n boundary r e g i o n s between maceral components, and we now have e x p e r i m e n t a l e v i d e n c e s u p p o r t i n g t h i s view. Thirdly, a l t h o u g h the homologue c o m p o s i t i o n s of the i r o n and g a l l i u m p o r p h y r i n s ( F i g u r e 3) a r e not i d e n t i c a l , t h e y a r e r a t h e r s i m i l a r . T h i s suggests to us t h a t they have s i m i l a r o r i g i n s . S i n c e the g a l l i u m p o r p h y r i n s a r e assumed t o a r i s e by m e t a l l a t i o n ( s i n c e s u c h complexes have not been d e t e c t e d i n the b i o s p h e r e ) t h i s i m p l i e s t h a t the i r o n p o r p h y r i n s a r i s e i n the same way. In o t h e r words t h i s e v i d e n c e , a l t h o u g h i n d i r e c t , suggests t h a t the i r o n p r e s e n t i n the hemes o b t a i n e d from c o a l i s not the o r i g i n a l i r o n p r e s e n t i n p o s s i b l e b i o l o g i c a l heme p r e c u r s o r s . However, we emphasise t h a t these are the f i r s t r e s u l t s o f t h i s s o r t t h a t have been o b t a i n e d , and f u r t h e r examples are c l e a r l y needed b e f o r e g e n e r a l i s a t i o n s can be made. m

C a l c i u m c a r b o n a t e i s not i n f r e q u e n t l y a s s o c i a t e d w i t h c o a l , and i t i s of i n t e r e s t i n the c o n t e x t of c o a l microcomponents to draw a t t e n t i o n t o a r a r e p i n k c a l c i t e from a h y d r o t h e r m a l a r e a i n A u s t r i a ( D e u t s c h - A l t e n b u r g ) which was i d e n t i f i e d as c o n t a i n i n g a g a l l i u m p o r p h y r i n by H a b e r l a n d t (14) i n 1944. We have o b t a i n e d a s m a l l amount of t h i s m i n e r a l which f l u o r e s c e s red i n u l t r a v i o l e t l i g h t . The e m i s s i o n spectrum o f the m i n e r a l i s shown i n F i g u r e 4, and i s t y p i c a l of a m e t a l l o p o r p h y r i n where the metal has a f i l l e d ( o r c o m p l e t e l y empty) d_ s h e l l . E x t r a c t i o n and chromatography r e v e a l m e t a l - f r e e p o r p h y r i n and a m e t a l l o p o r p h y r i n , which i s the major pigment component. The m e t a l l o p o r p h y r i n i s not a s i n g l e s u b s t a n c e , but i s p r e d o m i n a n t l y g a l l i u m ( I I I ) m e s o p o r p h y r i n IX ( t h e a x i a l l i g a n d i n the m i n e r a l i s not known) as shown by m e t a l s a n a l y s i s , t i c and h p l c comparisons, and mass s p e c t r o m e t r y . The comparison w i t h a u t h e n t i c c h l o r o g a l l i u m ( I I I ) m e s o p o r p h y r i n IX by h p l c - i n c l u d i n g c o i n j e c t i o n - i s shown i n F i g u r e 5. The o r i g i n of the m e s o p o r p h y r i n i s not known, but i n our view a b a c t e r i a l o r i g i n a s s o c i a t e d w i t h t h e h y d r o t h e r m a l n a t u r e o f the d e p o s i t deserves a t t e n t i o n . The s e q u e s t r a t i o n o f g a l l i u m i s a l s o not u n d e r s t o o d , but s t u d y o f t h i s type of d e p o s i t may i n the f u t u r e throw some l i g h t on the o c c u r r e n c e of g a l l i u m p o r p h y r i n s i n c o a l and l i g n i t e .


Metalloporphyrins

BONNETT ET A L .

Iron


Porphyrins c

Calcite

Gallium Janina

32

raw

181

Porphyrins

coal.


•30

L

29

C

31

C2I

i-ttrtUrf Vitrain

separated

from Janina

coat.

11 π ιι ιι ι g 111 Durain

100 η

separated

from Janina

i

coal

30Η

60'

40'

20Η

450

500

ii| n m m n 550

600

III l l l l l l

400

I | I I I I I M

4 50

ιριπιπιη'ΜιιιιΐΊΐιιιη 500 550 600

m/ζ

F i g u r e 3. Mass s p e c t r a o f m e t a l l o p o r p h y r i n s from J a n i n a c o a l and i t s v i t r a i n and d u r a i n l i t h o t y p e s (MS902, d i r e c t i n s e r t i o n , 3 0 0 ° C ) .




688

628

640

668

688

7ΘΘ

FLUORESCENCE

720

748

768

788

WAVELENGTH

Metal Complexes in Fossil Fuels - American Chemical Society

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