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Serine and cysteine thermal decomposition withrespect to fossil dating and carbonaceous meteorites
Item Type text; Thesis-Reproduction (electronic)
Authors Nagi, David Michael
Publisher The University of Arizona.
Rights Copyright © is held by the author. Digital access to this materialis made possible by the University Libraries, University of Arizona.Further transmission, reproduction or presentation (such aspublic display or performance) of protected items is prohibitedexcept with permission of the author.
Download date 08/06/2018 13:57:00
Link to Item http://hdl.handle.net/10150/557991
SERINE AND CYSTEINE THERMAL DECOMPOSITION
WITH RESPECT TO FOSSIL DATING AND CARBONACEOUS METEORITES
by
David Michael Nagi
A Thesis Submitted to the Faculty of the
DEPARTMENT OF GEOSCIENCES
In Partial Fulfillment of the Requirements for the Degree of
MASTER OF SCIENCE
In the Graduate College
THE UNIVERSITY OF ARIZONA
1 9 8 4
STATEMENT BY AUTHOR
This thesis has been submitted in partial fulfillment of requirements for an advanced degree at the University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.
Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of the source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgement the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.
SIGNED:
APPROVAL BY THESIS DIRECTOR
This thesis has been approved on the date shown below:
B. Nagy Date
Professor of Geosciences
ACKNOWLEDGEMENTS
This research was supported by the University of Arizona Graduate
Research Fund and NASA grant NGR 03-022-171o I thank Dr« Hiroshi
Ogino for technical help and Professors Bo Nagy, HoKo Hall Jr, and
JoFo Schreiber, Jr„ for their guidance*
I would like to also thank Tsuneko Ogino, Rich and Shelly Arinin,
Mike and Noreen Conarro, Randy Segal and Jane Allardt for their
companionship, during my stay in Tucson and in the future *
One sentence of acknowledgement doesn't even begin to express the
appreciation and thanks to my father and mother who have helped me
develop intellectually and emotionally* And my deepest thanks to my
wife Jane who found time in her life to set aside her career to share
in this achievement *
iii
TABLE OF CONTENTS
Page
LIST OF TABLES o o o o o o o o o « © o e o o o o © o © © o o v
LIST OF ILLUSTRATIONS vi
ABSTRACT o © © # © © © © © © © ® © © © © © © © © ® © © © © © "vn
1. INTRODUCTION. 1
Fossils© 6 0 © © 0 © 6 O Carbonaceous Meteorites.
12
2 © EXPERIMENTAL 7
Purification of Reagents . . . . . .Sample Preparations. . . . . . . . .TLC Separation . . . . . . . . . . .GC and IR Analysis © © . . © © . . .
78 910
3. RESULTS AND DISCUSSION. 12
Fossils © © © © © © © * © © © © © © © Carbonaceous Meteorites. . . . . © © ©
Condensation of Free Amino Acids.
121820
LIST OF REFERENCES. 22
iv
LIST OF TABLES
I o GC Nonhydrolysis of Hydrolysis Results» » e <> <> «, » <> <> <> 11
IIo Decomposition Yields of Serine and Cysteine 0 , 0 0 . 0 0 12
IIIo Glycine-Alanine Ratios of Serine Dehydration, , , , , , , 15
IVo Relative Yields of Alanine and Glycine From , , , , , , , 17Serine in the Presence of Troilite,
Page
v
LIST OF ILLUSTRATIONS
1 o Dehydration Mechanism of Serine and Cysteine
2 o Aldol Cleavage of Serine and Cysteine o o
Decarboxylation of Serine and Pyruvic Acid
Serine and Cysteine Rate Equations o o o » «>
o o o o o o o o o
o o o o o o o o o o
o o o o o o o o o
o o o o o o o
Alkaline Cleavage of the Disulfide Bond of Protein BoundAmino Acids o o o o o o o o o o o o o o o o o o o o o o
Complexation of Fe with Pyruvic Acid o o o o o o o
2+Six Member Fe Complex of Serine o o o o o o o o o o o o o
8 o Five Member Fe^ Complex of Serine o o o o o o o o
3
4
4
14
16
19
19
19
Page
vi
ABSTRACT
Decomposition of cysteine showed only alanine products as opposed
to serine which produces both alanine and glycine,, A comparison of
rates of decomposition can explain the low glycine - alanine ratios
found in fossil shellso Thermal exposure of serine in the presence of
FeS, troilite, gave larger yields of alanine and glycine. Theo+mechanism of decomposition is given as well as Fe complexes with
serine and pyruvic acid. These complexes are discussed in terms of
the catalytic effect observed. Hydrolysis results indicate
autocondensation of free amino acids in this abiotic system although
no peptides were found.
vii
CHAPTER 1
INTRODUCTION
The recent emphasis on organic sulfur compounds and their role in
abiotic reactions associated with carbonaceous meteorites as well as
biological influence on fossil diagenesis has expanded* The
electronegativity of sulfur gives increased versatility of chemical
reactions, reactions dominated by oxygen* Both applications are
discussed in this study*
Fossils
The potential application of amino acid diagenesis to fossil
dating has been noted a number of times (e*g* AbeIson, 1957;
Vallentyne, 1964; Hare, 1969)* More recently, the unstable hydroxy
amino acids serine and theonine (Vallentyne, 1964) have been applied
to fossil dating (Bada, Shou, Man and Schroeder, 1978; Steinberg and
Bada, 1983) due to their instability compared to more stable amino
acids* Other amino acids such as alloisoleucine have been used for
dating purposes (Wehmiller and Hare, 1971; Schreoder and Bada,
1977)* Another unstable amino acid which has not received enough
attention is cysteine, the sulfur equivalent to serine*
Two possible diagenetic reactions for serine have been proposed
(Wieland and Wirth, 1949)* These reactions can also be applied to
1
2
cysteine (Figure 1)» One path involves dehydration of serine Q ) to
pyruvic acid (2)o The alternative path involves aldol cleavage of
serine giving formaldehyde and glycine (Figure 2)o
Other reactions which influence serine levels in fossils (Figure
3), are decarboxylation of both serine and pyruvic acid leaving
ethanol amine (15) and ethanal (16) respectively.
It should be noted that the cysteine mechanism to form alanine is
probably the same as serine. However* some of the intermediates like
thiol pyruvic acid are very unstable and the alpha-mercapto acrylic
acid tautomer may actually be the reactive species.
Relative amounts of serine and cysteine have been determined for
several fossil shells (Hare* 1963; Degens and Love* 1965). Cysteine
is at least ten percent relative to the serine content and as much as
forty nine percent in the inner ligament of Mytilus shells (Hare,
1963). The availability of cysteine is apparent. The influence of
cysteine as it applies to fossil dating by serine diagenesis is part
of the text of this research.
Carbonaceous Meteorites
The famous contribution of the Miller-Urey (1959) electrical
discharge experiment sparked interest in abiotic synthesis of organic
compounds. The role of sulfur in terms of has expanded to the
latest models for meteorite formation and the resulting hydrocarbons
(Block and Wirth* 1971 )o The latest models involve Fishef-Tropsch
hoch2c h(nh2)COOH 1
H 2S M h2oHSCH2CH(NH2)COOH
H2S orH2C sC(,NH2)COOH — ---- >
3 H20
COOHh3c -c=o
HqC-C=S rzz H?C=C-S-H3 I ^ ICOOH COOH6 6°
H RCH 0i 2
C H o 1 3
H R C H o C H o
- H 2 R | 2 I L ,
C H - C H R H1 3 1 2 h 2 r
H - C - N ( H ) = C - R - H ------ H « C « N » C| | x
h - c ~ n = c --------------- >
I 1HOOC COOHCOOH COOH HOOC COOH
7 8 9
hrch2 c h3R-C-N(H)-C-H ----> CH3C(NH2)(H)COOHH COOH ioOH 11
IjO
R is oxygen or sulfur.
Figure 1. Dehydration Mechanism of Serine and Cysteine.
4
NH9I
h-o-c h2-c -cooh ---^ 0=CH2 + H2G(NH2)GOOHIH
1 12 . 1 4NH2IH-S-CHg-C-COOH --- ^ S=CH2 + 14H
2 13
Figure 2. Aldol Cleavage of Serine and CysteineNH0I VH-O-CHg-C-C
* ( 0-HH
1
ch35
hoch2ch2nh2 +
15
CH3CHO +
16
co2
CO2
SFigure 3* Decarboxylation of Serine and Pyruvic Acid.
5
synthesis using iron-nickel carbonyls in the presence of gas
(Block and Miller, 1971; Bierman and Michael, 1978)o Nevertheless, it
should be noted that observed discrepancies in the nitrogen
heterocyclic content of carbonaceous meteorites (Folsone, Lawless,
Romiez and Ponnamperuman, 1973; Hayatsu, Moore and Anders, 1975) have
not been adequately explained by this methodo Other synthesis models
include high energy reactions (Miller et alo, 1965)o
Regardless of the possible mechanisms of formation, analyses of
carbonaceous meteorites have revealed many classes of organic
compounds including amino acids (Nagy, 1968; Engel and Nagy, 1982)<,
Analyses has also revealed important sulfur compounds o An example is
the Murchison meteorite where the matrix, a layer-lattice silicate,
comprises 77 volume percent of the meteorite® The total sulfur
content has been determined at 1 <>6-2<>2 weight percent® Troilite
(ferrous sulfide) and pentlandite have abundances of Oo13 weight
percent with point counting and 7024 weight percent from bulk chemical
analysis (Fuchs, Olsen and Jensen, 1973)„ The point counting results
are low due to fine dispersion of these minerals in the matrix®
The role of sulfur compounds, such as troilite, may reveal
information concerning the stability and resultant distribution of
amino acids in meteorites® It should be noted, however, that the
comlexity of the mineral matrix of carbonaceous meteorites provides a
multitude of reactive environments in terms of supplying free ions and
heterogeneous catalytic surfaces®
6
The chemical environment for this portion of the study is
reducing and thus assimilates meteorite conditions<, This thermal
model consists of FeS (troilite), and serine*. The effect of
troilite on serine decomposition is the purpose of this portion of
this study
CHAPTER 2
EXPERIMENTAL
The use of amino acids at a micro analytical level requires a
complete contamination free environment<> To accomplish this level of
cleanliness many everyday laboratory methods were modified and other
meticulous procedures incorporatedo Many procedures took several
attempts to master the techniques involvedo
Purification of Reagents
All glassware and Teflon parts were washed in microcleaning
solutions with deionized water, then acid cleaned with hot 85 percent
and 15 percent concentrated and HNOg, respectivelyo
The 6N HC1 for hydrolysis work up was double distilledo The
O0O6N HC1 solution for ion exchange was a mixture of distilled 6N HC1 and triple distilled deionized watero
The 6N HC1, 2N NaOH and 1o5N HC1 for reconditioning and cleaning
the Dowex AG 50W-8X 50-100 mesh cation ion exchange resin was
formulated with triple distilled deionized water and stock 12N HC1 and
NaOH pellets; pellets were electronic grade purity*. the 204N NH^OH
for ion exchange elution was made with ultrapure NHg gas bubbled
through triple distilled deioninzed water»
The 2o6N HC1 in 1-Butanol for esterfication was prepared with
anhydrous HC1 gas vented across Fisher CAS registered 1-Butanol*. The
7
8
tare weight versus finished weight determined the molecular
concentrationso
Pentafluoropropionic anhydride and were not conditioned®
Blank samples showed no contamination from these stock solutions as
well as prepared solutions®
Sample Preparations
Solutions of 0®005g serine with 0®000g, 0®001g, 0®010g and 0®051g
of powdered FeS, ferrous sulfide, in 1®0ml of boiled, triple distilled
and deionized water were glass sealed under nitrogen® The sealed test
tubes were placed in a 100°C constant temperature heating block for
172®5 hours® At the end of the heating period the test tubes were
cooled to 25°C and opened® The sample was filtered on micropore 1®2
micron filters, with the sample container rinsed several times with a
0®06N HC1 solution®
A hydrolysis portion of the filtration was separated and dried
under nitrogen, double distilled 6N HC1 was added and the sample was again glass sealed® This sample was refluxed in a constant
temperature oil bath maintained at 100°C for 24 hours® The sample was
cooled and opened immediately®
Upon opening, the amino acid-bearing solutions, both hydrolyzed
and nonhydrolyzed samples, were dried under nitrogen and then
transferred in 0®06N HC1 to the cation ion exchange column® This
sample was washed with 25ml of phenolphthalein-tainted triple
distilled deionized water® The amino acids were then eluted with 2®4N
9
NH^OHo The sample was dried on a rotary evaporator and transferred to
a 2o5 dram reaction vial with O0O6N HC1, then dried under nitrogen and
solvent dried with CB.2^^2 0
Approximately 1o5ml of anhydrous I06N HC1 in butanol was used for esterification* Complete esterification took place after three hours
in a 100°C oil bath* Dried under nitrogen, the sample was acylated
with pentafluoropropionic anhydride (0*2ml) and (0*2ml)overnight*
TLC Separation
Thin layer chromatrography was done on precoated cellulose from
EM Laboratories* Separation of peptides was done with a
CH-^OHrCHClg :NH^OH~( 17%), (2:2:1) solvent* Seven 0*2 microliter spots
of a nonhydrolyzed sample with 180 minutes of solvent were
separated* Ninhydrin was used to locate the amino acid and polymer
fractions of one of the seven sample spots* Ultraviolet light located
the remaining sample fractions that were used for preparatory work
up* The slowest fraction was separated and the soluble compounds
extracted with water and then centrifuged* The sample was divided,
half for hydrolysis and half for direct esterification* The methods
of esterification were previously described* Retention ratios were as
follows: 0*601(ALA*), 0*523 (SER* and GLY0 ), 0*440 (residue
polymers)*
10
GC and IR Analysis
Sample analysis was done by gas chromatography using a Hewlett
Packard model 5880A with SP-2100 phase 25 meter by 0*25 millimeter
inner diameter fused glass columno Helium flow was 1o5mlo min * with
GC programme at 80°C to 190°C; an initial 80°C temperature was held
for five minuteso Sample injection size was 0*5 microliterso Amino
acids were assigned by coinjection and retention time*
Infrared spectra were determined on a Perkin Elmer model 137
spectrometer, Nonesterified samples, dried in the natural oil phase
and spread thinly over NaCl cells, were used. The spectrums were
taken on the slowest speed possible for best resolution. Polyethylene
film standards gave calibration for wavelength assignment,The
following is the list of assignments for the 0,051g sample in
reciprocal centimeters: 3400, 3000, 2650, 1970, 1745, 1600, 1510,
1410, 1280-1190, 1120, 1050, The HPLC analysis was done by Dr,
Michael Engel and William P, Lanier at the University of Oklahoma,
Table lo GC Nonhydrolysis and Hydrolysis Results<>
Nonhydrolysis Sample - FeS Alanine/Serinea Glycine/Serine3A - O.OOOg 0.147 ± 0.002 0.61 ± 0.01B - OoOOlg 0.68 ± 0.01 1.53 ± 0.04
C - O.OlOg 2.70 ± 0.04 6.9 ± 0.1
D - 0o051g 2.90 ± 0.08 7.2 ± 0.1
Hydrolysis^ Sample - FeS Alanine/Serine3 Glycerine/Serine3A - O.OOOg 0.145 ± 0.007 0.68 ± 0.01B - O.OOlg 1.01 ± 0.03 1.93 ± 0.02
C - O.OlOg 3.2 ± 0.1 7.3 ± 0.1
D - 0.051g 3.42 ± 0.07 8.00 ± 0.01
aAlanine and glycine serine is assumed tc
values are relative ) maintain a steady
to serine, state.
^Serine samples were exposed 172.5 hours at 100°C.
CHAPTER 3
RESULTS AND DISCUSSION
Fossils
Table II shows the yield of alanine and glycine from cysteine and
serine as a function of thermal exposure <> Cysteine degradation formed
no glycine *
Table II o Decomposition Yields of Serine and Cysteine <>
Alanine Glycine
Serinea 0ol45c 0 068cCysteine^ 1 „53^ none
aSerine exposed 172 05 hours at 100°C<,
^Cysteine exposed 32 05 hours at 100°Co
cAlanine and glycine values are relative to serine, serine assumed a steady stateo
^Alanine value is relative to cysteine, cysteine assumed a steady stateo
The lack of glycine expected to form from cysteine decomposition
can be explained in terms of the thiol being a good leaving group
producing dehydroalanine as opposed to the difficulty of cleaving a
carbon-carbon bond to produce thio formaldehyde»
12
13
It should be noted that if the cysteine decomposition mechanism
is the same as serine (Figure 1) the yield of alanine (Table II) may
give insight into the rate determining stepo Thiol pyruvic acid is
more reactive than the alkoxy pyruvic acid o This fact suggests that
slow step is where intermediate _7_ (Figure 1) is formed o
The argument could also be made that serine forms glycine whereas
cysteine does not, therefore, the aldol cleavage reaction is competing
with decarboxylation © .This could explain cysteine ?s greater
production of alanineo This argument does not apply to this study
because both serine and cysteine concentrations remain very large
compared to the products, where steady state assumptions can be made o
The implications of these results are twofold <> The source of
pyruvic acid would not only come from serine (Patchornik and
Sokolousky, 1964) but also from cysteineo Pyruvic acid has been
isolated from degradation of cysteine and cysteine peptides (Clarke
and Inouge, 1931; Nicolet, 1931)o
The reaction kinetics of pyruvic acid, which appear to be first
order as proposed (Steinberg et alo, 1983), may not necessarily change
with cysteine as a second source of pyruvic acido The combined rate
equation of serine and cysteine may remain first order as long as each
source of pyruvic acid remains first order and the mechanism of the
reaction does not change <>
It is only reasonable to consider that the rate constant
determined experimentally with fossil shells would be a combination of
14
both individual rate constant, as well as other influences of the
shell matrix such as metal ions (Metzler, Longenecker, and Snell,
1953; Metzler, Longenecker and Snell, 1954)» The metal ions would not
[CYS] --- ^ [PYR] (1)ks
[SER] -----^[PYR] (2)
kcs[CYS] + [SER] -----3, [PYR] (3)
d[PYR]/dt = kc [CYS] (1)d[PYR]/dt = kg [SER] (2)d[PYR]/dt = kcs [CYS] [SER] (30
Figure 4 „ Serine and Cysteine Rate Equationso
change the reaction order, if they remain a catalyst only, and if
there is no change in the mechanism of dehydration <> There is another
source of pyruvic acid not considered in the literature, the reverse
reaction of alanine producing pyruvic acido The kinetics require the
equations in Figure 4 to be irreversible first ordero The2+racemization reaction of alanine in the presence of Cu ions has
isolated pyruvic acid (Gillard, O ’Brien, Norman and Phipps, 1977)0
This reaction was found not to follow the first order kinetics
associated with serine decompositiono The apparent first order
kinetics determined the fossil shells may truly be pseudo first order
15
kinetics where one reactant concentration is essentially a steady
state forcing the overall reaction to appear first ordero
Empirically the cysteine influence will give larger values to
pyruvic acid than expected with serine dehydration aloneo Cysteine,
since it forms no glycine, will affect the glycine-alanine ratio®
Also, the cysteine rate of decomposition is greater, affecting the
glycine-alanine ratio and relative amounts of pyruvic acid and alanine
(Table III)® The increase in rate can be explained in terms of the
flexibility of sulfur to be a better leaving group and also a better
nucleophile than its alkoxy counterpart (Hipkin and Satchell, 1965)®
The glycine-alanine ratios published (Bada et al®, 1978) range from
0®76 to 1®48 in fossil shells® The data in Table III indicates a
glycine-alanine ratio three to six times greater®
Table III® Glycine-Alanine Ratios of Serine Dehydration®
Sample ALA/SER GLY/SER GLY/ALA
A 0®145 0®68 4®7
The foraminifera, mollusc and Chione shells used by Bada and
associates house the serine containing protein in a matrix, a matrix
which also influence the decomposition® Another possible influence is
the protein structure itself® The disulfide bond of the protein could
hinder degradation of cysteine® It has been found that the hydrolysis
of the disulfide bond is quite easy under mild alkaline conditions
16
(Asquith and Carthew, 1972); see Figure 5» It should be noted that
with each breaking of the disulfide bond, one dehydroalanine molecule
forms o
What may have a negative effect on serine fossil dating
reproducibility is the available hydrogen sulfideo The source of 2
can originate from degradation of cysteine inherent in the fossil
itself or externally from kerogen or sediment maturation (LeTran,
1971) or early in diagenesis from microbial activity, such as sulfate
reducing bacteria <> The equation in Figure 1 gives the reversible
reaction of l^S on serine (_1_) forming cysteine (_2) „
> > >N-H N-H N-HI \ OH I
CH-CHg-S-S-O^-CH -------C=CH2CO CO CO< 17 < < 3
>N-HI
HS-CHn-CHfCO
2 <
Figure 5 o Alkaline Cleavage of the Disulfide Bond, of Protein Bound, Amino Acids
Questions have arisen regarding the validity of serine going to
pyruvic acid, then alanine (Figure 1) (Wieland and Wirth, 1949)0 We
do agree that pyruvic acid is an intermediate of serine dehydration <>
Our experiments have shown that serine in the presence of pyruvic acid
almost completely goes to alanine in support of this mechanisme
17
Further study of the shell matrix and other diagenetic influences
are needed to make this method of dating reliableo Furthermore, basic
kinetic studies of serine and pyruvic acid and the correlation of
these studies to the diagenetic process are neededo Conclusions that
variations of temperature account for lack of reproducibility
(Steinberg et alo, 1983) are not justified* Even though temperature
has an exponential effect on the rate of reaction, in most cases,
other diagenetic effects have to be considered* The shell matrix,
sedimentary petrology, percolation of water and gases, microbial
action and depositional environment may be significant* Research
concentrated on these factors may provide the necessary information to
make amino acid fossil dating a reproducible and accepted method*
Table IV» Relative Yields of Alanine and Glycine From Serine in the Presence of Troilite*
Sample FeS Alanine3 Glycine3 GLY/ALAb
A O.OOOg 1.0 1.0 4.7
B O.OOlg 7.0 2.8 1.9
C O.OlOg 22.1 10.7 2.2D 0o051g 23.3 11.8 2.3
^Values are relative to serine, serine is assumed to maintainstate*
^Values are calculated from Table I.
18
Carbonaceous Meteorites
The use of troilite in this study is intended to reflect the
influence of one mineral on serine» Both compounds are constituents
of meteorites as previously described,,
The catalytic activity of FeS on serine decomposition is
twofold: The formation of and subsequent reaction with serine, asp+previously described, and the role of Fe ion as a-catalyst®
The role of Fe^+ ion on serine and cysteine decomposition is not 2+known, although Fe ion has been found to increase decomposition of
cysteine (Mori, 1957)o The Fe "*" ion will also complex with pyruvic
acid (Forsbers, Gellard, Ulmgren and Walberg, 1978)0 This may
stabilizze pyruvic acid as an intermediate and increase the formation
of alanine (Figure 6)® The Fe^+ ion in this complex would have
electron withdrawing effects and provide a more favorable situation
for nucleophilic substitution at the alpha position®
The glycine-alanine ratios possibly supports some kind of
stabilization® The ratios observed at a one milligram FeS level and
observed at the increased 51 milligram level indicate the importance
of the aldol cleavage reaction as it competes with the dehydration
reaction® The aldol cleavage reaction which forms glycine increases
relative to the dehydration reaction which leads to the formation of
alanine® It should be noted that catalytic effects of glycine may
also explain the observed changes in ratios®
Another possible complex of serine is the stabilized six member
conformation (Figure 7)® This six member complex where Fe^+ ion would
19
Figure 6
Figure 7
Figure 8
„ 2+O' \\\ O
/ C zH-X X 3 \ 0
2+Complexation of Fe with Pyruvic Acid
^ F ex-o
I II
H NH2 19
24-Six Member Fe Complex of Serine.
H ' X /O — C H2 \ ©
Five Member 2+ Complex of Serine.
20
have a similar electron withdrawing effect at the beta carbon-oxygen
position would lead to more favorable dehydration conditions for the
formation of alanineo The rate determining step would have to be the
loss of water rather than the reaction of pyruvic acid as proposed*
A pH effect may be present where increased pH increases the
formation of these complexes * The solutions were checked for pH and
they remained at pH 6-7* It is important to note that this system is
heterogeneous» Where FeS is a solid and serine is dissolved in water,
this could lead to local variations of pH on the surface of the solid
troilite* The increased formation of glycine is also indicated and
may be explained by the amine complex of serine (Figure 8)*
Condensation of Free Amino Acids
Thermal condensation of free amino acids has been accomplished in
both nonaqueous (Yamada, Tereshima and Wagatsuma, 1970; Fox and Dose,
1972; Saunders and Rohlfing, 1974) and aqueous systems (Jackson, 1971;
Weber and Orgel, 1979; Rao, Odom and Oro, 1980)* Our hydrolysis
results indicate condensation or polymerization of free amino acids
(Table 1)* Preparatory thin layer chromatography separation followed
by hydroloysis gave free glycine and serine amino acids* Gas
chromatography of samples B, C and D (Table 1) gave high molecular
weight peaks* These peaks had greater retention times than the
dipetide standards* We therefore report abiotic condensation of amino
acids in this aqueous system
21
One of the plausible reaction pathways for autocondensation to2-foccur in this sytem is the formation of a thiol ester* The Fe ion
present may have electron withdrawing effects on the carbonyl, if
complexed, making the carbonyl more reactive for nucleophilic attack
by the thiol anion* These results as well as others (Weber et al*,
1979) using thiol esters for autocondensation in abiotic models looks
promising* High performance liquid chromatography analysis confirmed
there were no dipeptides in these thermally exposed samples although
high molecular weight compounds were also observed*
Laboratory models of abiotic synthesis provide very limited
conclusions when applied to meteorites* the conclusions of this
thesis are derived from experimental resits of laboratory models *
These models reflect both fact and speculation of the chemical
environment of carbonaceous meteorites* Until analysis of meteorites
can be done without terrestrial contamination and no alteration by
analytical techniques with correlation of more than one sample, the
stated conclusions of this thesis are confined to the limits of
laboratory speculation
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Asquith, R <>S », and Carthew, P o, Biochem <> Biophys o Acta, 278, 8-14 (1972).
Bada, Jeffery L., Schreoder, Roy A., Naturwiss o, 62, 71 (1975) .
Bada, Jeffrey L., Shou, Ming-Yung, Man, Eugene H ., and Schroeder, Roy A o, Earth Plant « Sci <> Lett o, 41, 67-76 (1978) .
Bierman, L a n d Michael, K.W., The Moon and the Planets, 18, 477 (1978).
Bloch, M.Ro, and Miller, 0., Earth Planet* Sci * Lett*, 12, 134 (1971).
Bloch, M.R., and Wirth, H.L., The Meteoritical Society 34th Meeting1971, Experiments for Iron-Meteorites Simulation*
Bloch, M *R *, and Wirth, H*L*, Origin of Life, Ed* Y* Wolmen, D * Reidal Publishing, 65-71, 1981 *
Clarke, H *T *, and Inouge, J *M *, J . Biol* Chem *, 94, 541 (1931).
Degens, Egon T *, and Love, Steven, Nature, 205, 876-878 (1965)*
Degens, Egon T *, Spencer, Derek W ., and Parker, Robert H *, Comp*Biochem* Physiol *, 20, 553-579 (1967).
Engel, Michael H *, and Nagy, Bartholomew, Nature, 296, 837-840 (1982)*
Folsome, C *E *, Lawless, J *G *, Romiez, M *, and Ponnamperuma, C *, Geochim* Cosmochim* Acta, 37, 455 (1973)*
Forsbero, Ove, Gellard, Bertil, Ulmgern, Per, and Walberg, Olof, Acta Chem * Scand*, 32, 345 (1978)*
Fox, S *W*, Dose, K ., Molecular Evolution and the Origins of Life, Freeman: San Francisco 1972 *
Fuch, L *H *, Olsen E *, and Jensen, K *J *, Smithsonsian Contributions to the Earth Sciences; No* 10 (1973)*
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