The Formation Of The Amino Acid The Formation Of The Amino Acid Glycine In Extraterrestrial Ices Glycine In Extraterrestrial Ices

Philip D. HoltomPhilip D. Holtom

EPIC Meeting 2004 EPIC Meeting 2004

Tuesday 22Tuesday 22ndnd June 2004 June 2004

Slide2

OverviewOverview

• Introduction – Molecules in the ISM– Search for Glycine

• Experimental Setup– FTIR Spectroscopy

• Results– Observations and Mechanisms

• Future Work

Slide3

IntroductionIntroduction

• Over 130 molecules discovered in the Interstellar Medium (ISM)

• Range from simple diatomic, to complex long chain molecules

• More are being discovered each year with improved detection methods.

• Amino acids are becoming an important area of Astrochemical research. They are the building blocks of proteins and essential to life on Earth.

M17 - Swan Nebula Image © NASA, ESA, and J. Hester (ASU)

Slide4

Dust grainsDust grains

• Surface Chemistry in the ISM thought to occur on surfaces of dust grains in dense molecular clouds.

• Some of these grains are covered with an icy mantle formed by freezing out of atoms/molecules from the gas phase

•The ices in the mantle are bombarded with cosmic rays, Ions, solar UV, electrons.•Chemical modification occurs.

Slide5

Glycine – What is it ? Why study it ?Glycine – What is it ? Why study it ?

• NH2CH2COOH – The simplest amino acid

• Amino acids of the building blocks of proteins

• Higher homologues amino acids can be derived from glycine by replacing one hydrogen atom of the methylene group (CH2) by an organic group

• Amino acids have possibly been detected in the Interstellar medium (Kuan et al 2003)1

• Amino Acids have been formed in laboratory experiments from UV irradiation of ice samples, e.g. Caro et al 2002 Nature 416, 403 - 406 (28 March 2002)

• Detected in Meteorite samples– In excess of seventy amino acids

alone have been detected in the Murchison meteorite sample (Cronin, Cooper, and Pizzarello, 1995)2

1 Kuan, Y,Charnley, S.B., Huang, H.,Tseng, W., Kisiel, Z.,2003,ApJ,593,848

2 Cronin, J. R, Cooper G. W, Pizzarello S.,1995, Advances in Space Research,15, 91

Slide6

Glycine in the ISM ?Glycine in the ISM ?

• Kuan et al 2003 – The Astrophysical Journal,

593:848–867, 2003

• Searched for interstellar conformer I glycine (NH2CH2COOH), the simplest amino acid, in the hot molecular cores Sgr B2(N-LMH), Orion KL, and W51 e1/e

Kleinman-Low (KL) Region of the Orion NebulaSubaru Telescope, NAOJ

Slide7

Detection of Glycine Detection of Glycine

• 27 glycine lines were detected in 19 different spectral bands in one or more source

• They give no firm production pathways to glycine – remains to be determined!

Figure 2 – Glycine detection as reported by Kuan et al, 2003

Slide8

Pathways to GlycinePathways to Glycine

• Potential reaction pathways to form amino acids have also been investigated theoretically.

• Woon (2002) utilized quantum chemical modelling of astrophysical ices. He showed that one possible reaction mechanism for the formation of glycine is the recombination of the COOH (X2A’) radical with CH2NH2(X2A’).

Woon, D. E., 2002, ApJ, L177, 571

Slide9

A brief summaryA brief summary

• Glycine has possibly been detected in the ISM

• Amino acids have also been made in the laboratory from UV irradiated ice mixtures

• Theoretical / Experimental pathways need to be investigated in more detail

• One possible pathway is via CH2NH2 radicals

– These can be formed via Methylamine, CH3NH2

Slide10

Our experimentOur experiment• Experiments were performed at the

University of Hawaii at Manoa in collaboration with Prof. Ralf. Kaiser.

• 15l stainless steel chamber evacuated down to 810-11 torr

• Closed cycle helium refrigerator holds a polished silver mono crystal. This crystal is cooled to 10.8 0.2 K

• Nicolet 510 DX FTIR spectrometer (5000 - 500 cm-1) operates in an absorption–reflection–absorption mode (reflection angle θ = 75°)

Slide11

Experimental ProcedureExperimental Procedure

• Ice sample was prepared at 10 K by depositing binary gas mixtures of methylamine (CH3NH2; and carbon dioxide (CO2) onto a cooled silver crystal.

• Ice thickness & column densities determined by Beer-Lambert Law

• Column densities of carbon dioxide and methylamine of

2.00.4 1016 cm-2 and 7.20.21017 cm-2

respectively• Binary ice thickness of 44519 nm.

Slide12

After depositionAfter depositionFrequency

(cm-1)Molecule

Assignment

Characterization

3705 CO2 υ1 + υ3 combination

3598 CO2 2υ2 + υ3 combination

3296 CH3NH2 υ1 NH2 symmetric stretch

3001/2995 CH3NH2 υ11 CH3 antisymmetric stretch

2950 CH3NH2 υ2 CH3 antisymmetric stretch

2798 CH3NH2 υ3 CH3 symmetric stretch

2363 CO2 υ3 asymmetric stretch

2281 13CO2 υ3(13CO2) isotope peak

1594 CH3NH2 υ4 NH2 scissor

1504 CH3NH2 υ5

CH3 antisymmetric

deformation

1475 CH3NH2 υ12

CH3 antisymmetric

deformation

1413 CH3NH2 υ6 CH3 symmetric deformation

1357 CH3NH2 υ13 NH2 Twist

1167 CH3NH2 υ14 CH3 rocking (shoulder)

1146 CH3NH2 υ7 CH3 rocking

1041 CH3NH2 υ8 CN stretching (shoulder)

820 CH3NH2 υ9 NH2 wagging

667 CO2 υ2 in plane/out of plane bending

645 CO2 υ2(13CO2) isotope peak

0

0.1

0.2

0.3

0.4

5001000150020002500300035004000

2798

( 3

fro

m C

H3

NH

2)

2553

(C

H3

NH

2 /

CO

2 C

om

ple

x)

1357

( 1

3 f

rom

CH

3N

H2

)

2950

( 2

fro

m C

H3

NH

2)

2641

(C

H3

NH

2 /

CO

2 C

om

ple

x)

645

(2

from

13

CO

2)

667

(2

fro

m C

O2

)

820

(9

fro

m C

H3

NH

2)

1041

( 8

fro

m C

H3

NH

2)

1146

( 7

fro

m C

H3

NH

2)

1413

( 6

fro

m C

H3

NH

2)

1504

( 5

fro

m C

H3

NH

2)

1594

( 4

fro

m C

H3

NH

2)

2281

( 3

fro

m 1

3C

O2

)23

63 (

3 f

rom

CO

2)

3296

( 1

fro

m C

H3

NH

2)

3598

(2 2

+ 3

fro

m C

O2

)

3705

(1

+ 3

fro

m C

O2

)

2950

( 2

fro

m C

H3

NH

2)

2641

(C

H3

NH

2 /

CO

2 C

om

ple

x)

645

(2

from

13

CO

2)

667

(2

fro

m C

O2

)

820

(9

fro

m C

H3

NH

2)

1146

( 7

fro

m C

H3

NH

2)

1413

( 6

fro

m C

H3

NH

2)

1504

( 5

fro

m C

H3

NH

2)

1594

( 4

fro

m C

H3

NH

2)

2281

( 3

fro

m 1

3C

O2

)23

63 (

3 f

rom

CO

2)

3296

( 1

fro

m C

H3

NH

2)

3598

(2 2

+ 3

fro

m C

O2

)

3705

(1

+ 3

fro

m C

O2

)Wavenumber (cm

-1)

Ab

sorb

an

ce

Slide13

IrradiationIrradiation

• The ices were irradiated at 10 K for 60 mins with 5 keV electrons generated in an electron gun.

• Accounting for the extraction efficiency of 78.8 % of the electrons, the target is exposed to 1.8×1016 electrons over an irradiation time of 60 min

Slide14

Effects of IrradiationEffects of Irradiation

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

0.26

Abs

orba

nce

500 1000 1500 2000 2500 3000 3500 4000

Wavenumbers (cm-1)

-0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

0.26

Abs

orba

nce

500 1000 1500 2000 2500 3000 3500 4000

Wavenumbers (cm-1)

Figure 3 – Pristine CH3NH2 & CO2 mixture

Figure 4 – 60 minutes after irradiation of the mixture

Slide15

Effects of IrradiationEffects of Irradiation

• After irradiation we see new absorptions at 10K in our infrared spectrum. A selection of relevant ones are presented below.

frequency, cm-1 molecule assignment characterization

1381 NH3+CH2COO- νs COO COO symmetric stretch

1657 CO2- υ3 OCO asymmetric stretch

1846 HOCO υ2 CO stretch

2139 CO υ1 CO stretch

Slide16

After irradiation.After irradiation.

• Sample annealed

• Heated to 300 K

• Recooled to 10 K

• New infrared scan taken

• Residue seen on the silver substrate

Slide17

Spectrum after annealingSpectrum after annealing

0

0.02

0.04

0.06

0.08

0.10

1200140016001800

1335

cm

-1

1708

cm

-1

1667

cm

-1

1381

cm

-1

1416

cm

-1

1495

cm

-1

1596

cm

-1

Wavenumber (cm-1)

Abs

orba

nce

Slide18

Molecules observed in the residueMolecules observed in the residue

• Residue contains– Anionic Glycine– Zwittionic Glycine– Glycine isomers

Frequency

(cm-1)

Peak Area(cm-1)

Full WidthHalf Maximum

(cm-1)NH3

+CH2COO- NH2CH2COO- CH3NHCO2-

Column DensityNH3

+CH2COO-

(molecules cm-2)

Column DensityNH2CH2COO-

(molecules cm-2)

Column DensityCH3NHCO2

-

(molecules cm-2)

816 0.21 18.6 ν CC ν14 3.4 x 1015 3.4 x 1015

1005 0.43 44.3 ν13 6.5 x 1015

1143 0.62 72.1 ν11 1.4 x 1016

1335 4.6 88.6 νs COO ν9 3.55 x 1016 3.65 x1015

1381 0.6 36.8 νs COO ν8 4.6 x1015 1.2 x1015

1416 0.2 28.6 νs COO 1.5 x1015

1495 5.3 94.6 δs NH3 3.6 x1016

1596 9.5 87.1 νas COO 3.2 x1016

1667 4.2 64.3 ν5 1.8 x1015

1708 1.1 5.5 ν5 4.1 x1015

Slide19

Forms of GlycineForms of Glycine

• Zwitterionic glycine

• Anionic

O

O-

C

CH2

NH3+

“A zwitterion is a dipolar ion that is capable of carrying both a positive and negative charge simultaneously”

E.G. NH3+CH2COO-

Negatively charged, e.g. NH2CH3COO-

N

O

O-

CC

HH

H

H

Zwittionic Glycine

Anionic Glycine

Slide20

Recap..Recap..

• We irradiated a mixture of CH3NH2 and CO2 at 10K with 5 KeV electrons.

• We have seen possible evidence for glycine in our mixture after irradiation

• Both zwitterionic and anionic glycine may be present in the residue after annealing.

Slide21

What does this mean ?What does this mean ?

• It may be possible to create amino acids from simple binary mixtures of astrophysical ice

• Amino acids may also form in similar processes on comets subjected to cosmic ray and solar irradiation. They could then be delivered to earth.

• Possible pathways to interstellar glycine

Slide22

How could glycine form from our How could glycine form from our mixture ?mixture ?

• CH3NH2(X1A’) → CH2NH2(X2A’) + H(2S1/2)

•

CH3NH2(X1A’) → CH3NH(X2A’) + H(2S1/2)

Intense absorptions of the methylamine matrix do not allow a direct infrared spectroscopic detection of the CH2NH2(X2A’) and CH3NH(X2A’) species.

H + O C O

O

C O

H

O

C O

Hand/or

O

C O

H

H

C

H N

H

H

O C O+

H

C

H N

HH

C

O

O

H

C

H N

HH

O C

O

H

N

H C H

O C O+

H

H

N

H C

HH

C

O

O

H

N

H C

HH

C

O

O

(1)

(2)

(3)

(4)

(5)

(6)

Slide23

• Recall that in our irradiated mixture at 10K we observe the HOCO radical and the CO2

- anion.

• Superthermal hydrogen atoms can form HOCO in the ice matrix.

• One possible pathway to glycine is

HOCO(X2A’) + NH2CH2(X2A’) NH2CH2COOH(X1A’)

However for this to occur the reaction must take place between neighbouring radicals which hold the correct reaction geometry in the matrix cage

Slide24

SummarySummary

• We irradiated a mixture of Methylamine (CH3NH2) and Carbon Dioxide at 10K with 5 KeV electrons.

• We have the possible identification of glycine in the residue of the electron irradiated mixture of CH3NH2 and CO2

Slide25

Future WorkFuture Work

• Repeat the experiments to confirm the presence of glycine, through IR Spectroscopy and Chromatographic techniques

• Repeat the experiments using other sources that mimic the environments astrophysical ices are exposed to e.g. UV photons, Ion bombardment.

Slide26

AcknowledgementsAcknowledgements

• Prof Nigel Mason• Prof Ralf Kaiser• Mr Christopher Bennett• Dr. Yoshihiro Osamura• Dr Robin Mukerji• Dr Anita Dawes• Mr Mike Davis• EPSRC and PPARC

Slide27

Other Pathways To Glycine ?Other Pathways To Glycine ?

• Radical-radical recombination of an amino radical (NH2; X2B1) – generated via a cosmic ray particle induced nitrogen-hydrogen bond cleavage in a ammonia molecule - with the CH2COOH(X2A’) radical – formed by a carbon-hydrogen bond cleavage of the neutral acetic acid molecule

• (NH2 X2B1) + CH2COOH(X2A’) H2NCH2COOH(X1A’)

• Alternatively, suprathermal NH radicals which can be formed via coulomb explosions in the infra track of cosmic ray particles, can insert into the carbon-hydrogen bond of the acetic acid molecule to form glycine in a one-step reaction sequence

• NH(X3+) + CH3COOH(X2A’) H2NCH2COOH(X1A’)