The Formation Of The Amino Acid Glycine In Extraterrestrial Ices Philip D. Holtom EPIC Meeting 2004 Tuesday 22 nd June 2004

Slide2 Overview Introduction –Molecules in the ISM –Search for Glycine Experimental Setup –FTIR Spectroscopy Results –Observations and Mechanisms Future Work

Slide3 Introduction 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 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 ? NH 2 CH 2 COOH – 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 (CH 2 ) 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, (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 ? Kuan et al 2003 –The Astrophysical Journal, 593:848–867, 2003 Searched for interstellar conformer I glycine (NH 2 CH 2 COOH), 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 Nebula Subaru Telescope, NAOJ

Slide7 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 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 (X 2 A’) radical with CH 2 NH 2 (X 2 A’). Woon, D. E., 2002, ApJ, L177, 571

Slide9 A 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 CH 2 NH 2 radicals –These can be formed via Methylamine, CH 3 NH 2

Slide10 Our experiment Experiments were performed at the University of Hawaii at Manoa in collaboration with Prof. Ralf. Kaiser. 15l stainless steel chamber evacuated down to 8  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 ( cm-1) operates in an absorption–reflection–absorption mode (reflection angle θ = 75°)

Slide11 Experimental Procedure Ice sample was prepared at 10 K by depositing binary gas mixtures of methylamine (CH 3 NH 2 ; and carbon dioxide (CO 2 ) onto a cooled silver crystal. Ice thickness & column densities determined by Beer-Lambert Law Column densities of carbon dioxide and methylamine of 2.0  0.4  cm -2 and 7.2  0.2  cm -2 respectively Binary ice thickness of 445  19 nm.

Slide12 After deposition Frequency (cm -1 ) Molecule Assignme nt Characterization 3705CO 2 υ 1 + υ 3 combination 3598CO 2 2υ 2 + υ 3 combination 3296CH 3 NH 2 υ1υ1 NH 2 symmetric stretch 3001/2995CH 3 NH 2 υ 11 CH 3 antisymmetric stretch 2950CH 3 NH 2 υ2υ2 CH 3 antisymmetric stretch 2798CH 3 NH 2 υ3υ3 CH 3 symmetric stretch 2363CO 2 υ3υ3 asymmetric stretch CO 2 υ 3 ( 13 CO 2 )isotope peak 1594CH 3 NH 2 υ4υ4 NH 2 scissor 1504CH 3 NH 2 υ5υ5 CH 3 antisymmetric deformation 1475CH 3 NH 2 υ 12 CH 3 antisymmetric deformation 1413CH 3 NH 2 υ6υ6 CH 3 symmetric deformation 1357CH 3 NH 2 υ 13 NH 2 Twist 1167CH 3 NH 2 υ 14 CH 3 rocking (shoulder) 1146CH 3 NH 2 υ7υ7 CH 3 rocking 1041CH 3 NH 2 υ8υ8 CN stretching (shoulder) 820CH 3 NH 2 υ9υ9 NH 2 wagging 667CO 2 υ2υ2 in plane/out of plane bending 645CO 2 υ 2 ( 13 CO 2 )isotope peak

Slide13 Irradiation 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 1.8×10 16 electrons over an irradiation time of 60 min

Slide14 Effects of Irradiation Figure 3 – Pristine CH 3 NH 2 & CO 2 mixture Figure 4 – 60 minutes after irradiation of the mixture

Slide15 Effects 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 moleculeassignmentcharacterization 1381NH 3 + CH 2 COO - νs COOCOO symmetric stretch 1657CO 2 - υ3υ3 OCO asymmetric stretch 1846HOCOυ2υ2 CO stretch 2139COυ1υ1 CO stretch

Slide16 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 annealing

Slide18 Molecules observed in the residue Residue contains –Anionic Glycine –Zwittionic Glycine –Glycine isomers Frequenc y (cm -1 ) Peak Area (cm -1 ) Full Width Half Maximum (cm -1 ) NH 3 + CH 2 COO - NH 2 CH 2 COO - CH 3 NHCO 2 - Column Density NH 3 + CH 2 COO - (molecules cm -2 ) Column Density NH 2 CH 2 COO - (molecules cm -2 ) Column Density CH 3 NHCO 2 - (molecules cm -2 ) ν CCν x ν x ν x ν s COOν9ν x x ν s COOν8ν8 4.6 x x ν s COO1.5 x δ s NH x ν as COO3.2 x ν5ν5 1.8 x ν5ν5 4.1 x10 15

Slide19 Forms of Glycine Zwitterionic glycine Anionic “A zwitterion is a dipolar ion that is capable of carrying both a positive and negative charge simultaneously” E.G. NH 3 + CH 2 COO - Negatively charged, e.g. NH 2 CH 3 COO - Zwittionic Glycine Anionic Glycine

Slide20 Recap.. We irradiated a mixture of CH 3 NH 2 and CO 2 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 ? 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 mixture ? CH 3 NH 2 (X 1 A ’ ) → CH 2 NH 2 (X 2 A ’ ) + H( 2 S 1/2 ) CH 3 NH 2 (X 1 A ’ ) → CH 3 NH(X 2 A ’ ) + H( 2 S 1/2 ) Intense absorptions of the methylamine matrix do not allow a direct infrared spectroscopic detection of the CH 2 NH 2 (X 2 A ’ ) and CH 3 NH(X 2 A ’ ) species.

Slide23 Recall that in our irradiated mixture at 10K we observe the HOCO radical and the CO 2 - anion. Superthermal hydrogen atoms can form HOCO in the ice matrix. One possible pathway to glycine is HOCO(X 2 A ’ ) + NH 2 CH 2 (X 2 A ’ )  NH 2 CH 2 COOH(X 1 A ’ ) However for this to occur the reaction must take place between neighbouring radicals which hold the correct reaction geometry in the matrix cage

Slide24 Summary We irradiated a mixture of Methylamine (CH 3 NH 2 ) 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 CH 3 NH 2 and CO 2

Slide25 Future 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 Acknowledgements 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 ? Radical-radical recombination of an amino radical (NH 2 ; X 2 B 1 ) – generated via a cosmic ray particle induced nitrogen-hydrogen bond cleavage in a ammonia molecule - with the CH 2 COOH(X 2 A ’ ) radical – formed by a carbon-hydrogen bond cleavage of the neutral acetic acid molecule (NH 2 X 2 B 1 ) + CH 2 COOH(X 2 A ’ )  H 2 NCH 2 COOH(X 1 A ’ ) 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  +) + CH 3 COOH(X 2 A ’ )  H 2 NCH 2 COOH(X 1 A ’ )