Cosmic-ray and UV induced processes within mixed ices and at formamide :

mineral interfaces

School of Chemistry and Biochemistry

Georgia Institute of Technology

Atlanta, GA USA

School of Chemistry and Biochemistry

Georgia Institute of Technology

Atlanta, GA USA

T. M. Orlando, G. Grieves, M. Dawley,H. Barks, N. Hud, and Ernesto Di Mauro

JPL NAI Titan Kickoff Meeting, July 8, 2009

JPL NAI-Titan as a Prebiotic Chemical System

Image from NASA Website

We are interested in cosmic ray, solar-photon and impact induced surface chemistry.

I Cosmic ray (i.e. low-energy electron) interactions with ice.

II. Reactive scattering with trapped methane. Formation of CO, CO2, HCOOH, etc.

III. Reactive scattering with PAHs, Tholins and graphite to form sugar precursors.

IV. The importance of another bio-solvent – formamide (NH2COH). Nulceobase formation on mineral surfaces. A plausible route to RNA?

Figure from 2008 JPL-NAI proposal Surfaces chemistry can mean aerosol surfaces as well as Titan’s surface.

Orlando Research Group Simulating Titan’s atmospheric aerosol surface chemistry.

UHV-Surface Science “ideal” conditions - Metal oxides and mineral surfaces

Mineral/surfaces reactions under Low-temp/higher pressure conditions

Generating Vacuum Ultraviolet (VUV) Photons – Third Harmonic Generation

VUV photons can be used to generate aerosols and in sensitive detection of desorbed products using-SPI*:

High sensitivity

High ionization efficiency

Little or no fragmentation

355 nm

118 nm

P3 ω = N2 | χ(3 ω)|2 P ω3 F(b,Δk, L)

P: laser densityN: number density of Xenon χ: linear susceptibility ω: input angular frequencyF: phase matching function b: confocal beam parameterΔk: wave-vector mismatchL: length of medium

Xe

355 nm 355 nm

118 nm

85 nm* Ediristinghe, P.D.; et al. Anal. Chem. 2004, 4267-70

Laser based methods for multidimensional MS analysis of complex hydrocarbon mixtures

Nd:YAG Laser

Nd:YAG Laser

Pulse Generator

Amplifier

Oscilloscope

Data Acquisition

TOF

118nm 355nm

MCP

LiF Lens

Turbo Pump

Gate Valve

Loading Chamber

Mechanic Pump

ManipulatorLoading Dock

Linear Stage

Sample Stage with XYZ Movement Control, 360° Rotation Control, and Temperature Control

VUV THG Cell(Xenon)

Mass(m/z)

50 75 100 125 150 175 200 225 250 275 300 325 350

Rel

ativ

e In

tens

ity

0

1000

2000

3000

4000

5000

6000

4:His+

5:Arg+

6:Trp+

***

1

2

3

4

5

6

****

1:Gly+

2:Gln+

3:Met+

a

cd

b

58

a: [His - 74]+

b: [Gln - 45]+

c: [Met - 45]+e

d: [Arg - 45]+

e: [Trp - 74]+

•Analyzing complex hydrocarbon mixtures using two-step laser desorption and photoionization.

•Couple this to 2-D GC methods

UHV system to simulate cosmic ray bombardment

Ice surfaces produced under ultrahigh vacuum (2x10-10 torr)

Surface cooled by closed cycle helium refrigerator and heated resistively for TPD

Surface is irradiated with 1-100 eV electrons from pulsed electron gun

•Electron induced production and desorption of products measured with TOF, REMPI-TOF and QMS.

•Also equipped with an FTIR (during and post irradiation).

Post-Irradiation TPD: D2O with CH4 dosed in pores

• CH4 at 16 amu shows low temperature desorption and release during pore collapse

• N2 (from background) and CO at mass 28 also released from pores

• CO2 is retained until the ice overlayer desorbs at 190 K – forms only at the interfacesGrieves and Orlando manuscript in prep.

100 eV

200 nA 2 hours

rastered

Measuring ion yields from PAH’s, tholins or graphitic inclusions/substrates?

Polyunsaturated fragments are produced which resemble graphite step-edge plus oxidized functional groups. This is with less than 1ML of water present. Oxidation is very facile.

0

500

1000

1500

2000

2500

3000

0 10 20 30 40 50 60 70 80 90 100

Mass (AMU)

CH3+

H2O+

H+

H2+

(HCCH)H+

HCO+

HCCO+

H3CCO+

C3H3-6+

C4H5-9+

HOCO+

C5H5-9+

x10

0

0.2

0.4

0.6

0.8

1

1.2

35 37 39 41 43 45 47 49

C3H3+

39

C3H5+

41

C3H7+

43

HCCO+

1 2 3 4 5 6 7 8 9 10 11 12 13

What about oxidants from PAH’s, tholins or graphitic inclusions/substrates?

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

1 2 3 4 5 6 7

IR reflectance spectra of tholins (Sample from Mark Smith, UA).)

Tholins/Ice mixture - BlackPure Tholins - Blue

A two-tier system – VUV induced formation of aerosols.

Analyzing deposited material-IR reflectance, FTIR, Auger, Raman

Can deposit micron sized “grains”

TPD of NH3 and HCN.

Can formamide reactions occur during impact events?

Figure from 2008 JPL-NAI proposal

Speculation –

Perhaps formamide chemistry was important during impact events?

High temperature excursions could have occurred. (Calculations on longevity of impact oases on Titan: 103-104 yrs. (O’Brien, Lorenz, and Lunine, Icarus 173, (2005) 243

NH3 may be needed with limited amount of water.

.

• This component of Theme 3 will address:• the VUV and low-energy electron induced formation of organic

aerosols via gas-phase photochemical and low-energy electron induced nucleation processes.

• the uptake, “dissolution” and oxidation of these organic aerosols by condensed ices and simulated cosmic ray bombardment.

• laser desorption, single-photon mass spectrometry analysis of complex organic mixtures produced by photochemical deposition.

• silicate, phosphate mineral reactions with HCN, nitriles and possibly formamide which may lead to polymer and nucleobase formation.

Visit us at http://web.chemistry.gatech.edu/~orlando/epicslab/Tholin work in collaboration with T. McCord and M. Smith

Retention Time (Minutes)0 5 10 15 20 25 30

Re

lativ

e In

ten

sity

(A

rbitr

ary

Un

its)

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4No CatalystCaCO3Na4P2O7

1

23

4

x105

Retention Time (Minutes)0 5 10 15 20 25 30

Re

lativ

e In

ten

sity

(A

rbitr

ary

Un

its)

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4No CatalystCaCO3Na4P2O7

1

23

4

x105

130 oC for 48 hours

Heating formamide produces only purine unless minerals are present

Effects of mineral catalysts and The presence of radiation. (UV

light)?

• Mineral catalyst required to produce anything but purine

• Nonspecific product distributions reduces requirement for particular minerals

• Synergistic with mineral catalysts, UV light further enhances synthesis rather than purely degradation.

5 guanine

2 allopurinol

3 adenine

1 purine

4 hypoxanthine

formamide

, h

Retention Time (Minutes)0 5 10 15 20 25 30

Re

lativ

e In

ten

sity

(A

rbitr

ary

Un

its)

-0.20.00.20.40.60.81.01.21.41.61.82.0

No Catalyst

CaCO3 Catalyst

Na4P2O7 Catalyst1

2

3

4

5

Retention Time (Minutes)0 5 10 15 20 25 30

Re

lativ

e In

ten

sity

(A

rbitr

ary

Un

its)

-0.20.00.20.40.60.81.01.21.41.61.82.0

No Catalyst

CaCO3 Catalyst

Na4P2O7 Catalyst1

2

3

4

5

UV light expands product diversity

Testing the chemistry

•Time series measurement of the production of adenine from UV irradiated formamide at 130 oC.

•Triangles represent adenine from neat formamide irradiation (magnified twenty times), while diamonds are for the same experiment spiked with 10 mg DAMN in 4 mL.

•The dashed-line with diamonds represents no UV.

Time (hours)

0 12 24 36 48 60 72 84 96

Yie

ld ( g

/ g

form

amid

e)

0

20

40

60

80

100

120

140

160

DAMN plus UV

UV (x20)

DAMN no UV

Scheme 1. Route to formation of adenine from formamide. After thermal degradation of formamide into HCN and water. Reactions proceed via HCN polymerization and are enhanced by mineral catalysts. Spiking with DAMN accelerates both the thermal and nonthermal routes to adenine formation but the UV photochemical route results in significantly higher yields.

formamide

O

H2N

H +

DAMN

AICN

UV

adenine

N

N

NH2

N

HN

AMN

N

N

NH2

NH2HN

N

H2N

NC

NH2

CN

NCHCN

H2O

H2O18 post irradiation

Post irradiation TPD after electron irradiation of methane in H2O18 ice: Production of CO2

18

• No mass coincidence for CO2, CO2

18

We observe all the following masses

• 44 = CO2

• 45 - HOCO

• 46 = O16CO18

• 48 = CO218

CO2 is formed due to reactions with CO and hot/mobile O as well as via HCO and OH. The yield above 190 K is likely a surface/interface reaction

Post irradiation TPD after electron irradiation of

methane in H2O18 ice: Production of CO18

Use O18 labeled water to distinguish between background N2 (mass 28) and stimulated production of CO (mass 28)

CO18 (mass 30)

• Unirradiated sample releases some mass 30 (NO or HCOOH contaminant) during sublimation.

• Irradiated mixture releases mass 30 (primarily CO18) during pore collapse

pore collapse

Mass (a.m.u.)

0 10 20 30 40 50 60 70 80

Inte

nsity

(ar

b.un

its)

0

200

400

600

800

1000

Graphene oxideGrapheneH+

CH3+

H3O+

HCO+

HCCO+

C3Hx+

C2Hx+

C4Hx+

C5Hx+

An example of electron-stimulated removal of edge-sites and defects from epitaxial graphene and graphene-oxide

The H+ yield is very high for both surfaces

There are high mass hydrocarbons fromboth substrates.

There are O-containing Fragments from the graphene oxide.

The total cross sectionfor hydrogen removal is ~10 -19 cm2

Incident electron energy - 50 eV

Post Irradiation TPD: D2O

D2O + CH4 (pores) unirradiated D2O + CH4 (pores) irradiated

Grieves, Orlando, Blake manuscript in prep.

100 eV

200 nA 2 hours

Rastered over 1 cm2

~ 1015 e- /cm2 total dose

0

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45

0

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30Biological building blocks for

RNA and DNA from Formamide? • Formamide provides plausible routes to nucleobase formation, nucleoside phosphorylation and nucleic acid polymerization.

• Saladino and Di Mauro laboratories have demonstrated purine formation from formamide in the presence of mineral catalysts. Review: Chemistry and Biodiversity Vol. 4, 694 (2007)0

5

10

15

20

25

30

purine

adenine

hypoxanthine

uracil

cytosine

dihydrouracil

urea

parabanic acid

formylglycine

carbodiimide

mg

prod

uct p

er g

form

amid

e

cytosine

guanine

allopurinol

hypoxanthine

adenine uracil

purine cytosine

cytosine

formylglycine

formylglycine

Na3PO4

Ludlamite

Hureaulite

Turquoise

purine

formamide