Objectives

This experiment is a simulation of experiments a chemist would be doing in analyzing organic materials from a meteorite. The difference is the size of the sample - you will be given more organics than the actual amount that can be isolated from an average-size meteorite. Also, you will develop a method for searching for two specific chemicals that are suspected to exist on meteorites, but their presence has not been confirmed as yet.

Background

Guanazole, a heterocyclic compound (1), was hypothesized to be an important candidate for prebiotic self-replicating systems since it is a mimic of diaminopyrimidine [1]. Urazole (2) is another such candidate, since it mimics uracil. The structures of 1 and 2, including the compounds that they mimic, are shown below. The arrows indicate the H-bonding sites that would be involved in the recognition of the complementary base pairs. It is clear that 1 and 2 have similar H-bonding patterns as the compounds they mimic. In the pre-RNA world, 1 and 2 could be involved in the primordial genetic systems, as they have an advantage over the present-day bases, such as uracil, that they make nucleosides non-enzymatically, by a reaction with sugar in an aqueous medium [1]. It is suspected that both 1 and 2 should be found on meteorites, since they can form easily under simulated prebiotic conditions from chemicals that are found in the interstellar space. However, a question arises if guanazole's presence on meteorites can be easily detected due to its known ability to make complexes with various metals [2-4] that might be present on meteorites. If guanazole were not liberated in an unchanged form from its metal complexes during the standard extraction procedure of organics from the meteorites, one would miss its possible presence on meteorites. The same applies to the metal complexes of urazole, some of which we have recently prepared in our laboratory.

Experimental

To solve the above problem, you will first prepare complexes of 1 with several metals that could be found on meteorites, by following the procedures given below. You will identify these complexes via their IR spectra and elemental analysis. Then you will try the same procedures with 2 to synthesize metal complexes of 2. The first step, then, is preparation of the metal complexes.

After you prepare the complexes, you will imagine that they are the material that is found on a meteorite. You will need to "extract" the metal complexes from the rest of the imaginary meteorite. In your case, the "extraction" would be actually the process in which you will dissolve the complexes in some solvent, such as water, ether, methylene chloride, alcohol, dilute acid (HCl), or dilute base (NaOH). Thus, the second step is to dissolve the metal complexes in a suitable solvent.

In the third step you will evaluate the stability of the metal complexes under the extraction procedure you used, and will try to liberate guanazole from its metal complexes. You will find out if guanazole survived the procedure and if it could be recovered without destruction. This part of the experiment you will design and conduct independently. You need to do the following: 

1) Design a mild method for the decomposition of the guanazole-metal complex, which would lead to a recovery of guanazole, but would not cause its chemical destruction. Perform the experiment. 

2) Design the extraction procedure for the recovery of the organic component from the reaction mixture from 1). The organic material will be presumably guanazole, but possibly also some of its decomposition products. The method for extraction of the organic material should have an emphasis on the quantitative aspect of recovery. Perform the extraction. 

3) Perform spectral analyses of the extracted organic component. 

4) Assign the structure of the organic component as pure guanazole, impure guanazole, or some other product. 

5) Identify impurities in the organic component, if any. 

6) Calculate the percent recovery of guanazole from the guanazole-metal complex. This would be your recovery of guanazole from the meteorite. Repeat the same sequence for the urazole metal complexes.

Experimental Procedures

I a,b,c: Synthesis of Metal Complexes (Me = Co, Ni, Zn) of Guanazole (1)[2]

Guanazole (1) (0.349 g; 3.5 mmol) is dissolved in warm water (1.5 mL) and then acetone (8.0 mL) is added. Next, the solution of metal nitrate (0.5 mmol) to be used [a) Co (NO3) 2 .6H2O, or b) Ni (NO3) 2 .6H2O, or c) Zn (NO3) 2.6H2O] in 2.0 mL of acetone is added while stirring. The complexes should precipitate rapidly. They are digested on a water bath for half an hour, washed with acetone, and dried in a vacuum desiccator. The IR spectra are taken in Nujol mull or KBr pellet.

I d. Synthesis of Iron (III) Complex of Guanazole (1)[3]

A solution of 1 (0.68 g, 0.006 mol) is dissolved in 50% ethanol (3.0 mL) with heating and mixed with iron (III) nitrate (0.24 g) dissolved in ethanol (4.0 mL). The precipitate is filtered off, washed with water and ethanol, and dried first in air, and then in a vacuum desiccator. The compound obtained is Fe (guanazole) 3(NO3) 3. 0.5 H2O. Please record the IR spectrum.

I e. Synthesis of Silver (I) Complex of Guanazole (1)[4]

Dissolve 0.5 mmol of solver (I) nitrate in a small volume of water and then add 2.0 mL of acetone. Dissolve separately 1.5 mmol of 1 in a small volume of warm water and 8.0 mL of acetone. Mix both solutions. A white complex will precipitate rapidly. It should be washed with acetone and dried in a vacuum desiccator. Please record the IR.

II a-e. Synthesis of Metal Complexes of Urazole (2)

Repeat the procedures above, with the same number of moles, but use urazole (2) instead of guanazole (1). Carefully record any observations. Urazole forms complexes much slower that guanazole does. Set up a reflux apparatus and start with a minimum of 4 hrs of reflux.

Please observe: Not all students will be preparing all the complexes. Please see your instructor for the individual assignments.

References:

 [1] V. M. Kolb, J. P. Dworkin and S. L. Miller, J. Mol. Evol., 38, 549-557 (1994). 

[2] M. Gabryszewski and B. Wieczorek, Polish J. Chem., 73, 2061-2066 (1999). 

[3] M. L. Barmin, E. L. Kasatikova, I. B. Karaulova and V. V. Mel'nikov, Russian J. Coord. Chem., 22, 434-437 (1996). 

[4] M. Gabryszewski and B. Wieczorek, Polish J. Chem., 72, 2352-2355 (1998). 

Structure of guanazole, 1. Please notice the presence of several tautomers.

The structures of 1 and 2, including the compounds that they mimic. The arrows indicate the H-bonding sites that would be involved in the recognition of the complementary base pairs.

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