SERINE AND CYSTEINE THERMAL DECOMPOSITION WITH RESPECT...

32
Serine and cysteine thermal decomposition with respect 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 material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 08/06/2018 13:57:00 Link to Item http://hdl.handle.net/10150/557991

Transcript of SERINE AND CYSTEINE THERMAL DECOMPOSITION WITH RESPECT...

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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

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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

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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

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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

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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

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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

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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

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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.

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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

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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

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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.

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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.

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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®

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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

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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

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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

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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)*

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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,

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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.

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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

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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

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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

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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

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(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

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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.

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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

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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.

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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

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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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