Ab Initio Calculations and Raman and SERS Spectral Analyses of Amphetamine Species

Abstract

For the first time, the differences between the spectra of amphetamine and amphetamine-H + , and between different conformers are thoroughly studied by ab initio model calculations, and Raman and SERS spectra are measured for different species of amphetamine. The spectra of amphetamine and amphetamine-H + samples were obtained and assigned according to a comparison of the experimental spectra and the ab initio MO calculations, performed using the Gaussian 03W program. The analyses were based on complete geometry minimisation of the conformational energy of the S-plus-amphetamine molecule and the S-plus-amphetamine-H + ion. The harmonic frequency calculations provide information about the characteristic features of the Raman spectra and the nature of the bonding in the molecule. It is concluded that vibrational bands from salt anions with internal bonds (sulfates, hydrogen phosphates, etc.) need to be taken into account when employing these spectra for identification purposes. These results also show how Raman spectroscopy can assist the forensic community in drug profiling studies. Furthermore, as their spectra are different, discrimination between the free and protonated forms of amphetamine salts can be observed. Here, we provide evidence for this difference, and show experimentally, how it has been overseen.

Raman Optical Activity and Raman Spectra of Amphetamine Species—Quantum Chemical Model Calculations and Experiments

“…Determination of the ratio of one enantiomer to the other, or the content of impurities in a sample has been a subject for different biophysical methods. However, we have earlier shown that confusions in determination of these molecules and in describing them were surprisingly more common than expected [9]. In that work, we showed that by using Raman and surface enhanced Raman spectroscopy (SERS) combined with quantum chemical DFT calculations, it was possible to demonstrate the differences between what people almost agreed on to be AMP and what really has been measured.…”

“…We have earlier found the Raman spectra of AMP, obtained by quantum chemical calculations or experimentally to be sensitive to the internal rotational degree of freedom around the C7-C8 bond [9]. The rotational geometry can influence the structure of the molecule, so that changes can be seen in the vibrational spectrum, as it will be shown below for the ROA spectra.…”

“…We studied the internal rotations in AMP, i.e. rotation of the bonds attached to the chiral C8 atom, as it can be seen in impurities, which gave a high background level of fluorescence in the spectra [9]. This necessitated cleaning of the sample solutions by centrifugation and filtering, carried out by microspinning for 5 min at 1000 rpm in filter vials (Lida Microspin Filter, 0.2 μm PES, PP w/RCV + cap, Cat# 8508-00).…”

Integrated waveguide and nanostructured sensor platform for surface-enhanced Raman spectroscopy

“…The benefit of SERS lies with its ability to effectively "fingerprint" chemical species applicable to a wide variety of fields including material science, 12,13 biochemistry and biosensing, [2][3][4][5][6][14][15][16] and electrochemistry. 17,18 The dominant mechanism for most SERS processes is electromagnetic enhancement from the amplification of light by the excitation of localized surface plasmon resonances.…”

“…These vibrational transitions are dependent on the molecules; therefore, the inelastic scattering can be used to identify functional subgroups of the test molecule. 1 Devices capable of molecular detection are of great interest for many applications including cancer cell detection, [2][3][4] drug analysis, 5,6 and explosives detection. 7,8 Although extremely useful for bulk sample identification, conventional Raman spectroscopy has limited applications as the level of detection of the inelastic-scattered light is very low.…”