Abstract
Illicit drugs and their trafficking require worldwide efforts in investigation, detection, and control. Colorimetric tests are often applied to identify drugs. Cocaine has some well-known adulterants that can provide a false positive response. Cucurbit[6]uril (CB[6]) has been suggested as a potential detector for cocaine and other illicit drugs. This work uses in silico methods to evaluate the use of CB[6] to detect cocaine and these interfering substances. More specifically, this work analyzes different possibilities of CB[6] complexation with cocaine, lidocaine, caffeine, and procaine and compares the results achieved for cocaine and its adulterants. Different methodologies were employed: quantum chemistry was investigated through DFT B3LYP/TZVP (density functional theory-Becke, three-parameter, Lee-Yang-Parr with triple zeta valence plus polarization basis set) and the semi-empirical methods Austin model 1 (AM1), parametric methods 3, 6, and 7 (PM3, PM6, PM7), and Recife model 1 (RM1). We used these methodologies intending to compare the reasonability and reproducibility of the results in the gas phase condition. Solvent influence was studied by molecular dynamics (MD) simulations. Results showed that CB[6] does not bind to these substances, as judged from the positive values of binding free energy obtained with all methods. DFT and MD were the most reliable methods whereas semiempirical ones were not reproductible in describing these systems. Results also showed that interactions are not specific, so CB[6] does not provide a good response for cocaine detection.
Highlights
Drug trafficking and consumption are worldwide concerns, and integrated efforts are needed to combat them
We observe that the DFT calculation returned positive values for the Gibbs free energy, evidencing that encapsulation was not spontaneous even when exothermic values were obtained for enthalpic contribution
We identified a stable conformation of the CB[6]-caffeine complex in at least one molecular dynamics (MD) simulation replicate, in which the drug’s six-membered ring was inserted in CB[6], whereas the other two poses were unstable during their respective MD simulations (Figure 4)
Summary
Drug trafficking and consumption are worldwide concerns, and integrated efforts are needed to combat them. Correct drug identification is essential to ensure human rights: it can prevent the arrest of innocents and avoids the miscarriage of justice.. Correct drug identification is essential to ensure human rights: it can prevent the arrest of innocents and avoids the miscarriage of justice.2,3 It is important in harm reduction projects because there are advantages in testing drugs before they are consumed. Presumptive tests are less time-consuming and less expensive. Most of these tests consist of colorimetric tests and can give doubtable results.. The Scott test is the most widely employed for cocaine identification in law enforcement actions. It can return false positives because cocaine is not sold in its pure form. Confirmatory tests are more trustful, despite being more expensive as they require specialized equipment, trained examiners, and complex sample preparation, besides they
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