Cosolvent Exclusion Drives Protein Stability in Trimethylamine N-Oxide and Betaine Solutions.

Using a combination of molecular dynamics simulation, dialysis experiments, and electronic circular dichroism measurements, we studied the solvation thermodynamics of proteins in two osmolyte solutions, trimethylamine N-oxide (TMAO) and betaine. We showed that existing force fields are unable to capture the solvation properties of the proteins lysozyme and ribonuclease T1 and that the inaccurate parametrization of protein-osmolyte interactions in these force fields promoted an unphysical strong thermal denaturation of the trpcage protein. We developed a novel force field for betaine (the KBB force field) which reproduces the experimental solution Kirkwood-Buff integrals and density. We further introduced appropriate scaling to protein-osmolyte interactions in both the betaine and TMAO force fields which led to successful reproduction of experimental protein-osmolyte preferential binding coefficients for lysozyme and ribonuclease T1 and prevention of the unphysical denaturation of trpcage in osmolyte solutions. Correct parametrization of protein-TMAO interactions also led to the stabilization of the collapsed conformations of a disordered elastin-like peptide, while the uncorrected parameters destabilized the collapsed structures. Our results establish that the thermodynamic stability of proteins in both betaine and TMAO solutions is governed by osmolyte exclusion from proteins.

Can X-Ray Powder Diffraction Be a Suitable Forensic Method for Illicit Drug Identification?

New psychoactive substances (NPSs) are associated with a significant number of intoxications. With the number of readily available forms of these drugs rising every year, there are even risks for the general public. Consequently, there is a high demand for methods sufficiently sensitive to detect NPSs in samples found at the crime scene. Infrared (IR) and Raman spectroscopies are commonly used for such detection, but they have limitations; for example, fluorescence in Raman can overlay the signal and when the sample is a mixture sometimes neither Raman nor IR is able to identify the compounds. Here, we investigate the potential of X-ray powder diffraction (XRPD) to analyse samples seized on the black market. A series of psychoactive substances (heroin, cocaine, mephedrone, ephylone, butylone, JWH-073, and naphyrone) was measured. Comparison of their diffraction patterns with those of the respective standards showed that XRPD was able to identify each of the substances. The same samples were analyzed using IR and Raman, which in both cases were not able to detect the compounds in all of the samples. These results suggest that XRPD could be a valuable addition to the range of forensic tools used to detect these compounds in illicit drug samples.

Structure of heroin in a solution revealed by chiroptical spectroscopy.

In this work, the 3-D structure of the well-known opioid drug heroin in a solution was investigated. The goal was to provide a complete and detailed description of the stable conformers with their relative abundances. This knowledge is very important from the pharmaceutical and forensic point of view as it could help significantly with deeper understanding of heroin's metabolism and the development of antagonist medicines for the case of an overdose. As heroin is a chiral compound with five stereogenic centres, the methods of chiroptical spectroscopy supplemented by density functional theory (DFT) calculations were applied to study its conformations in chloroform solution. The selected chiroptical methods, namely, electronic circular dichroism (ECD) and vibrational circular dichroism (VCD), are inherently sensitive to the 3-D structure of small- to medium-sized chiral organic molecules. A thorough conformational analysis revealed four stable conformers of heroin in chloroform solution, where the conductor-like polarizable continuum model of the solvent was used for all the calculations. The simulated ultraviolet (UV), infrared (IR), ECD, and VCD spectra were compared with the experimental ones and very good agreement was found, which enabled a detailed structure description and interpretation of the spectra. Chiroptical spectroscopy in combination with DFT calculations proved to be a very sensitive tool for the analysis of the 3-D structure of heroin in a solution in contrast with conventional spectroscopic methods. Especially, the application of VCD seems to be a promising approach for monitoring structural changes, for instance, those caused by solvents or interactions with other agents.

Cocaine Hydrochloride Structure in Solution Revealed by Three Chiroptical Methods.

Structure and flexibility of natural compounds determine their biological activity. In the present study, electronic circular dichroism (ECD), vibrational circular dichroism (VCD), and Raman optical activity (ROA) spectra of cocaine hydrochloride in aqueous solutions were measured and related to the structure with the aid of density functional theory (DFT) computations. Additional measurements in deuterated environment made assignment of vibrational bands easier. The results suggest that the prevalent cocaine conformation in solution differs from that adopted in hydrochloride crystal. The spectroscopic results and computational analysis are consistent with X-ray structures of known cocaine-receptor complexes, in which the compound adopts a variety of conformations. All three kinds of chiroptical spectra exhibited significantly greater conformational sensitivity than unpolarized absorption or Raman scattering. The ROA technique provided the largest number of well-resolved bands, bearing rich structural information.