Amino Acid Alanine Reactivity With the Fingerprint Reagent Ninhydrin: A Detailed Ab Initio Computational Study

• NCJ Number: 216797
• Journal: Journal of Forensic Sciences Volume: 51 Issue: 6 Dated: November 2006 Pages: 1267-1275
• Author(s): Nicholas D.K. Petraco Ph.D.; Gloria Proni Ph.D.; Jennifer J. Jackiw Ph.D.; Anne-Marie Sapse Ph.D.
• Date Published: November 2006
• Length: 9 pages
• Publication Format: Article
• Publication Type: Report (Study/Research)
• Language: English
• Country: United States of America

Annotation

This paper reports on a computational study of the mechanisms and reaction energetics (science that deals with the laws of energy and its transformations) of the formation of Ruhemann's Purple (intensive colored compound) from ninhydrin (one of the most widely used reagents for the chemical development of fingerprints on porous surfaces) and alanine (representative amino acid contained in latent fingerprints).

Abstract

The study computed the chemical structures and energetics for three proposed mechanisms of formation for Ruhemann's Purple from ninhydrin and an alpha-amino acid, using high-level ab initio quantum chemical calculations. The results imply that under relatively high temperatures (approximately 100 degrees C), where excess energy is abundant, each chemical step in all three mechanisms is energetically feasible. The multiple-reaction paths open to Ruhemann's Purple formation help to explain the higher yields at these temperatures. Using the study's computations as a guide, researchers also determined the mechanisms for the formation of Ruhemann's Purple at a temperature of approximately 25 degrees C, which is a reasonable temperature at which ninhydrin would be applied to fingerprints in the field. The scheme basically follows that of the McCaldin mechanisms, with the primary difference being intermediate 5 of the McCaldin mechanism being replaced with 5' from the Lamothe mechanism. This work is significant for forensic science, because obtaining information about the energetics of the mechanisms of reaction between ninhydrin and amino acids could lead to the design of better analogues of ninhydrin or other alternatives. The long-term goal of these computations is to help the forensic chemistry community obtain products with stronger chromo-fluorogenic properties to aid in detecting fingerprints at crime scenes. 3 tables, 7 figures, and 36 references