What Quantum Chemistry Can Do for Forensic Science

1. Danielle Sapse and Nicholas D. K. Petraco John Jay College of Criminal Justice City University of New York What Quantum Chemistry Can Do for Forensic Science Amino Acid Alanine Reactivity with the Fingerprint Reagent Ninhydrin. H=E

2. Outline • How a Quantum Chemist can Help Forensic Science • History and Trivia on Fingerprints • Ninhydrin + Alanine Gives Ruhemann’s Purple • Results • Future Applications for Forensic Science • More fingerprints • Explosives detection • Probes for illegal drugs

3. Forensic Science – Quantum Chemistry A Potential Synergy • Opportunity to improve communication between theorists and (bio) analytical chemists and biologists • Computer speed always improving and big molecular systems can be treated • Theory can't replace the lab but can help!

4. What Can We Learn From Y? • Energy and Structures of Molecules • Molecular orbitals and relative energetics to help understand reactivity • Structures help us understand reactivity and design useful molecules such as materials, drugs and probes • Electronic Spectra • Vibrational, Rotational Spectra • NMR and ESR Spectra • Thermodynamic data from Statistical-Mechanics

5. A Forensic Science Classic: Fingerprints! • Palm prints used for human identification in courts perhaps as early as 1st century Roman Empire • 7th century China, was perhaps the first documented use of fingerprints as means of identification. • It was probably Faulds (1880) who first proposed exploiting fingerprints for criminalistics in modern times. • As a means of identification, fingerprints are still par excellence.1

6. Fluorescence, Phosphorescence I.S.C. Singlet Exc. State Triplet Exc. State Fluorescence Energy Phosphorescence Laser Closed Shell Ground State Fingerprint Amplification • Latent prints, only trace amounts of biomaterial • Very hard or impossible to see by themselves. • Solution: Use some kind of developing agent.

7. Menzel et al. After Fingerprint Amplification • Fingerprint fluorescence is faint • Treat fingerprint with materials to obtain fluorescent or phosphorescent compounds Menzel et al. Before

8. ninhydrin Ruhemann’s purple Ninhydrin-Ruhemann’s Purple System • Ninhydrin first suggested to develop latent fingerprints in 1950’s. • Ninhydrin reacts with amino acids in fingerprints to produce Ruhemann's purple • Brightly colored and easy to identify by eye • Fluoresces slightly at the 582 nm and 407 nm when treated with a zinc or cadmium salts • Starting material, ninhydrin, is cheap

9. Motivation • Synthesize new compounds with properties superior to Ruhemann's purple. • No known chemical system which offers significant advantages in color to Ruhemann’s purple. • Ultimately we want to help improve chromogenic and fluorogenic properties • An unequivocal understanding of the mechanism of formation for Ruhemann’s purple is important! • The mechanism for the reaction between amino-acids and ninhydrin was never fully settled. • McCaldin Mechanism • Lamothe Mechanism • Friedman Mechanism • We have attempted to understand these mechanisms using ab-inito computations.

10. Computational Methods • Structures of all molecules in McCaldin, Lamothe and Friedman mechanisms optimized at RHF-SCF level using a 6-31G* basis set and analytic derivative methods. • Gradients optimized to > 0.0001 a.u. • Largest Abelian point groups used • Harmonic vibrational frequencies computed for all structures using finite difference of analytic gradients. • All computed structures found to be energetic minima • Benchmark structures for ninhydrin, alanine and Ruhemann’s Purple were found using DFT B3LYP and a 6-31G**.

11. DFT Benchmark Structures Ruhemann’s Purple ninhydrin

12. CO2 Strecker degradation intermediate Strecker degradation ninhydrin + a-amino acid aldehyde dehydration and hydrolysis hydrindantin and possible side products several intermediates Ruhemann’s Purple General Scheme for the Reaction of Ninhydrin with a-amino acids to form Ruhemann’s Purple

16. Our postulated mechanism at 25oC

17. New HF-6-31G** Results on Substituted Ninhydrin-Ruhemann’s Purple Systems

18. Forensic Science – Quantum Chemistry • Future Projects • Compute low lying excited electronic and vibrational states to predict fluorescent/ phosphorescent ability • Tailor molecules to cheap portable lasers! • Ruhemann's Purple-Transition Metal-Halide • Explore substituted ninhydrines • Derivatives of indanediones • Quantum Dots! • Clusters of Atoms • Exotic quantum properties • Phosphoresce well

19. Forensic Science – Quantum Chemistry • Explosives Detection • Live in an age of terrorism • Many articles to examine • Ideally testing must be • Fast and user friendly • Portable • Safe and reliable • Lanthanide complexes • Have been useful for finger prints • Phosphoresce well • Coordinate well with explosives • Quantum Dots

20. Forensic Science – Quantum Chemistry • Quantum Chemistry can help with design • Metal and Ligand excited states • Determine efficiency of metal-ligand energy transfer process • Indicate ligand structures to prevent binding of unwanted species • Metal-Ligand possibilities • Europium, Terbium • Derivatives of thenoyiltrifloroacetone and othrophanthrolene • Quantum dots • CdS, CdSe, GaAs, InAs

21. Forensic Science – Quantum Chemistry N N CF3 S O O thenoyiltrifloroacetone othrophanthrolene

22. Forensic Science – Quantum Chemistry • Molecular Sensors • Miniaturization to the molecular level • Improve selectivity and detection limits • Widen range of detectable analytes • Sensor modeling allows optimization of response properties to analyte • Important factors • Molecular topology • Binding site geometry • Binding and stabilizing interactions • Few probes for illegal drugs, yet many binding sites

23. Forensic Science – Quantum Chemistry • Molecular Sensors for canabinols and amphetamines • Species are of reasonable size NH OH O R O C5H11 O Canabinol 3,4-Methylenedioxymethamph.

24. Forensic Science – Quantum Chemistry R R • Ferrocene based barbiturate sensors N O N O HN HN R Fe N O HN R Fe O N HN

25. Acknowledgments • John Jay College of Criminal Justice • Our co-authors: • Prof. Anne-Marie Sapse • Prof. Gloria Proni • Jennifer Jackiw • Our collaborators and colleagues: • Prof. Thomas Kubic • Chris Chen • Chris Barden • Prof. Jon Riensrta-Kiracofe • Detective Nicholas Petraco (NYPD ret.) • Officer Patrick McLaughlin (NYPD)