Endogenous production of organic molecules

The variation of reaction rate with temperature follows the Arrhenius equation, which we have used to study the rate of chemical reactions in the interstellar medium ISM (Section 5.4, Equation 5.9), and can be applied to the liquid phase or reactions occurring on surfaces. Even the smallest increases in temperature can have a marked effect on the rate constants, as can be seen in the increased rate of chemical reactions at body temperature over room temperature. Considering a reaction activation energy that is of the order of a bond energy, namely 100 kJ mol-1, the ratio of the rate constants at 310 K and 298 K is given by  

Chemistry within the body is approximately five times faster than in a test tube at room temperature. The reverse is true, of course, with chemical reactions in liquid methane at 100 K some 1.2 x 1035 times slower than at 298 K. Neutral chemical reactions remain slow in solution at 100 K if they have a significant activation barrier. As with the ISM, chemistry involving breaking of chemical bonds is frozen out at 100 K and has direct implications for chemistry on the surface of Titan, for example. 

The period of emergence of life on Earth is constrained to be between the period 4.0-3.7 Gyr ago, for which there is no fossil record. Urey postulated that all of the planets formed from the same solar nebula and so the early Earth should have an atmosphere with a composition the same as that of Jupiter (known at the time), 

Estimates of the total lightning energy contribution to the atmosphere are placed at 1.8 x 1022—1 x 1024 eV m-2 yr 1. From the experiments it is possible to work out a yield of all amino acids per electron-volt passed into the experiment. The calculation for glycine is 2 x 10-5 molecules eV-1 for a methane environment and 

If this is an important production reaction for amino acids, what concentrations are required globally to generate the amino acid budget and should this represent a global concentration within the oceans The concentrations of HCN and NH4 1 are limiting in this process and HCN in particular is familiar from comet chemistry. Amino acids seem to be synthesised rather easily in the chemistry of a reducing atmosphere or from exogenous delivery. 

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Chyba C, Sagan C. Endogenous production, exogenous delivery and impact-shock synthesis of organic molecules an inventory for the origins of life. Nature 1992 355 125-132. 

Chu, L. and C. Anastasio (2003) Quantum yields of hydroxyl radical and nitrogen dioxide from the photolysis of nitrate on ice. Journal of Physical Chemistry A, 107, 9594-9602 Chyba, C. and C. Sagan (1992) Endogenous production, exogenous delivery and impact-shock synthesis of organic molecules An inventory for the origins of life. Nature 355, 125-132 doi 10.1038/355125a0... 

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