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Transcript of Sigam o Nitrogênio - USP › ~amancio › aga0316_notas › 15aga0316_nitrogen_1.pdfAbundances of...
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Sigam o Nitrogênio
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FOLLOW THE LIFE
• Solvent
• Biogenic elements
• Source of Free Energy
searches for life within our solar system commonly retreat from a search for life to a search for “life as we know it,” meaning life based on liquid water, a suite of so-called “biogenic” elements (most famously carbon), and a usable source of free energy.
(Chyba & Hand, 2005, p. 34)
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FOLLOW THE LIFE
• Follow the water
• Follow the carbon
• Follow the nitrogen
• Follow the energy
• Follow the entropy
• Follow the information
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Why Nitrogen?
• N is the fourth more abundant chemically active
element in the Universe
• N is one of the elements (together with N, C, O
and P) entering in the composition of the carrier
of biological information in Earth (DNA)
• N allows the assembling of a number of
complex, heterocyclic, assymetric compounds
• The odd-valence of N compounds introduces
asymmetries, which are a necessary condition for
information storage
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Four types of organic
macromolecules
in living systems.
Most of the molecules in the living systems are
water (H2O) and large organic
macromolecules:
• Carbohydrates
• Lipids
• Proteins
• Nucleic Acids
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Proteins
• “Proteios” – primary
• Long “trains” of amino acids
• Different proteins have different sequence of amino acids
• 20 amino acids used in any organism
• Some provide structure (fingernails, hair)
• Some serve as catalysts
• Enzymes – proteins with catalitic properties
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Polymerization
• A polymer is a substance composed of
molecules with large molecular mass
composed of repeating structural units, or
monomers, connected by covalent
chemical bonds. Well known examples of
polymers include plastics and DNA.
http://en.wikipedia.org/wiki/Molecular_masshttp://en.wikipedia.org/wiki/Structural_unithttp://en.wikipedia.org/wiki/Monomerhttp://en.wikipedia.org/wiki/Covalenthttp://en.wikipedia.org/wiki/Chemical_bondhttp://en.wikipedia.org/wiki/Plasticshttp://en.wikipedia.org/wiki/DNA
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L-Alanine Glycine
Linked by dehydration reaction
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Proteins
• “Proteios” – primary
• Long “trains” of amino acids
• Different proteins have different sequence of amino acids
• 20 amino acids used in any organism
• Some provide structure (fingernails, hair)
• Some serve as catalysts
• Enzymes – proteins with catalitic properties
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Proteins (continued)
• Even though there are ~70 amino acids
any known life uses only 20
• Amino acids derived abiotically are a mix
of both “left-handed” and “right-handed”
ones. Biological amino acids are only left-
handed.
Chirality
• Was there a common ancestor for all life?
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Biology uses only
left-handed Alanine
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Amino acids synthesized in laboratory:
The Miller-Urey-Experiment
FIRST EXPERIMENTAL FORMATION OF BIOLOGICALLY
RELEVANT MOLECULES UNDER PREBIOTIC CONDIDTIONS
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Murchison (1969, Australia)
Amino acids found in the space:
The Murchinson Meteorite
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Does Chirality come from outer space?
Enantiomeric Excesses in Meteoritic Amino Acids
Pizzarello and Cronin, Geochim. Cosmochim. Acta 64, 329-338 (2000)
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En
anti
om
eric
Exc
ess
(%)
Murchison
Murray
2-A
min
o-2
,3-d
imeth
yl-
pe
nta
no
ic a
cid2
S,3
S/2
R,3
R
2S
,3R
/2R
,3S
Iso
vali
ne
a-M
eth
yln
orv
ali
ne
a-M
eth
ylv
ali
ne
a-M
eth
yln
orl
eu
cin
e
a-M
eth
yl-
n-b
uty
ric
ac
id
No
rva
lin
e
Ala
nin
e
Va
lin
e
Mechanisms?
Racemization?
Amplification?
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Meteorites represent the only extraterrestrial
material which can be studied on Earth !
Volatile fraction:
Insoluble C-fraction:
60-80 % aromatic carbon
highly substituted small
aromatic moieties branched
by aliphatic chains
Murchison (1969, Australia)
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Abundances of soluble organic compounds in the Murchison meteorite (Botta & Bada 2002, Sephton 2002, 2004)Compound Class Concentration(ppm)
Amino Acids CM 17-60CI ~5
Aliphatic hydrocarbons >35
Aromatic hydrocarbons 3.3
Fullerenes > 1
Carboxylic acids > 300
Hydroxycarboxylic acids 15
Dicarboxylic acids &
Hydroxydicarboxylic acids 14
Purines & Pyrimidines 1.3
Basic N-heterocycles 7
Amines 8
Amides linear > 70
cyclic > 2
Alcohols 11
Aldehydes & Ketones 27
Sulphonic acids 68
Phosphonic acids 2
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Difficulties of the organic synthesis
via Meteorites
• Simple organics only – no
macromolecules
• It is hard to accumulate necessary mass of
carbon for the “concentrated” prebiotic
soup.
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Building Macromolecules:
Polymerization
• Polymerization produces longer molecules
from simple organic molecules
• One type of polymerization is through the
loss of water
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Minerals can help polymerization• Organic soup was probably too dilute to form very long
molecules
• Minerals (like clay) can provide a repeating pattern to act as a template for polymerization
• Small organic molecules could have stuck to the mineral surface
Kaolinite
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Catalysts in Chemistry
• Suppose chemical reaction:
A + B → AB is a slow reaction
• The same reaction can be accelerated with catalyst (D):
A + D → AD fast step
B + AD → AB + D fast step
The net result is still:
A + B → AB but it is much faster
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Some Proteins are Catalysts
• They are the Enzymes - the largest class of proteins.
• They accelerate the rates of several biological reactions
• They are typically named based on the reaction that they catalyze, and have suffixes with the letters -ase. Example:
Protease (e.g. trypsin, carboxypeptidases)
Lactace (hydrolyzes milk sugar)
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Nucleic acids (DNA/RNA)
• Deoxyribonucleic acid (DNA), is a
nucleic acid that contains the
(genetic) instructions used in the
development and functioning of all
known living organisms.
• Collection of nucleotides linked
together in long polymers – the
largest macromolecule
http://en.wikipedia.org/wiki/Nucleic_acidhttp://en.wikipedia.org/wiki/Geneticshttp://en.wikipedia.org/wiki/Developmental_biologyhttp://en.wikipedia.org/wiki/Life
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Each nucleotide:
1) Five-carbon sugar molecule
2) One or more phosphate groups
3) Nitrogen-containing compound –
nitrogenous base
Nucleotide
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Strand
DNA strand DNA strand
A T
T A
G C
C G
Hydrogen bond
(weak)
A can link only with T
G can link only with C
Watson and Crick (1953) realized
that DNA have a double helix.
Two DNA strands are “complimentary”
to each other
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DNA vs. RNA
• Deoxyribonucleic acid (DNA) –deoxyribose sugar
• Ribonucleic acid (RNA) – ribose sugar
Four bases:
DNA RNA
A – adenine – A
G – guanine – G
C – cytosine – C
T – thymine U – uracil
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Pyrimidines
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Nitrogenated Organic Compounds
in Astrobiology
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H2O
CO
CO2CH3OH
NH3CS2HCN
SO2
CH4C2H2C2H6H2CO
OCS
MOLECULAR STRUCTURE OF THE COMA
CO+
CO2+
O+
H2O+
H3O+
OH
HI
NH2S2CN
SO
NS
HNC
C2, C3
H2CO CO
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Sagittarius B2
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Horse Head Nebula
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CHO Molecules
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Nitrogenated Molecules
(Abundances relative to CN)
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Simple Organic Molecules
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Using Isotopic Fractionation (D, C13, N15, O18)
to explore production channels
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Nitriles
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Bell et al. 1997. On the Detection of Cyanodecapentayne,
HC11N, in TMC-1. Astrophys. J. 483, L61–L64
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Nitriles
C2N2 – cyanogen
HC3N – cyanoacetylene
HC5N – cyanodiacetylene
CH3CN – acetonitrile
CH2CHCN – acrylonitrile
CH3C3N – methylcyanoacetylene
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From Nitriles to
Nitrogen Heterocyclic
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Simple heterocyclic compounds
to be aimed in future observations of the
interstellar and circumstellar medium
oxazole pyrrole pyridine
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Titan as a Benchmark
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Formation of Pyridine in Titan
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Produção de Heterocíclicos em Titan
(Krasnopolsky, 2009)
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Propenal and Propanal
in Sgr B2(N)
(Hollis et al. 2004)
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Formation of pyrrole from butenal
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Formation of pyrrole from s-triazine
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Formation of pyridine from pyrrole
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PAH-Heterocyclic Connection
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PAHs: extremamente resistentestempo de sobrivência no ISM ~ 1 Gano
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O PAH pode perder hidrogênios, pois a energia necessária para a perda de um átomo de hidrogênio é 4,5 eV
Um parâmetro adicional que descreve um PAH é o seu grau de hidrogenação, αH/C
Desidrogenação de PAHs
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Incorporation of
Nitrogen Atoms
into PAHs
(Ricca et al. 2001)
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H
C
N
Which PANHs viable?
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A PAH Channel for Production of Pyridine
The PAHs have typically ~ 50 C atoms per PAH
Pericondensates with D6h symmetry: C6n²H6n
n=3 C54H18
C54H18 + γ → C54H17 + H
C54H18 + H → C54H17 + H2C54H17 + HCN → C55H18N + γ
C55H18N + C2H2 → C57H19N + H
C57H19N + γ → C54H18 + HC3N
C57H19N + C2H4→ C54H18+ C5H5N
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PAHs and PANHs (root PAH C54H18)
Pericondensates with D6h symmetry: C6n²H6n
n=3 C54H18
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Channels for Production of Pyridine
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Production of pyrrole vs. pyridine
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Densidades de Coluna
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IRC+10216 (AGB star)
N < 7.3-8.6 x 1012 cm2
CRL 618 (PN)
N < 2.3-2.7 x 1013 cm2
Searchs for Pyridine in the ISM(Charnley et al. 2005)