Ninhydrin Reaction with Alanine in Latent Fingerprints
This is an ab initio computational chemistry project and all energies of the compounds in this multi-step reaction were calculated via WebMo, using Hartree-Fock 6-31G geometry optimization.
Background
Fingerprinting is an important tool used in forensic science and solving crimes. Latent fingerprints is one of the easiest ways to connect an individual with the crime. These types of fingerprints are created when any surface is touched and there is a transfer of a thin layer of chemical residue from the tips of your fingers. Multiple methods of lifting fingerprints are available, but chemical methods is the most effective for nonporous surfaces.1 In this project, I am focusing on the use of ninhydrin to lift a fingerprint. Ninhydrin reacts with the proteins in the latent fingerprint and create an amino acid residue that becomes a purple color after a multi-step reaction. The ninhydrin condenses the primary amine of an amino acid, alanine in this case, to form an imine. The resulting imine decarboxylates and hydrolyzes in water to form another primary amine that condenses with a second ninhydrin molecule to form Ruhemann's purple.2
Calculations
| Structure | Energy (Hartree) | Run Time |
|---|---|---|
| Ninhydrin | -643.27 | 7.3 sec |
| Alanine | -321.77 | 2.1 sec |
| 1 | -889.50 | 27.6 sec |
| 2 | -626.84 | 21.3 sec |
| 3 | -548.97 | 10.6 sec |
| Acetaldehyde | -152.91 | 0.6 sec |
| 4 | -625.77 | 16.7 sec |
| 5 | -1041.85 | 43.0 sec |
| 5' | -1117.79 | 50.4 sec |
| 6 | -568.77 | 9.7 sec |
| 7 | -568.84 | 9.9 sec |
| 8 | -1128.16 | 7 min 11 sec |
| 9 | 547.69 | 9.7 sec |
| 10 | -567.65 | 4.9 sec |
| 11 | -813.39 | 24.3 sec |
| 12 | -625.82 | 14.1 sec |
| Ruhemann's purple, isomer 1 | -1040.48 | 1 min 15 sec |
| Ruhemann's purple, isomer 2 | -1040.57 | 1 min 1 sec |
| Ruhemann's purple, isomer 3 | -1041.07 | 2 min 43 sec |
| Water | -75.98 | 0.6 sec |
| Carbon Dioxide | -185.58 | 0.6 sec |
| Ammonia | -56.10 | 0.6 sec |
Citations
1. Friesen, J.B. Forensic Chemistry: The Revelation of Latent Fingerprinting. Journal of chemical education, 2015. 92: p. 497-504.
2. Petraco et al. Amino Acid Alanine Reactivity with the Fingerprint Reagent Ninhydrin. Journal of Forensic Science, 2006. 51: 6. p. 1267-1275.