In search of the mutual relationship between the structure, solid-state spectroscopy and molecular dynamics in selected calcium channel blockers

Forced Solid-State Oxidation Studies of Nifedipine-PVP Amorphous Solid Dispersion

In the present study, the oxidative degradation behavior of nifedipine (NIF) in amorphous solid dispersions (ASDs) prepared with poly(vinyl pyrrolidone) (PVP) with a short (K30) and a long (K90) chain length was investigated. The ASDs were prepared via dry ball-milling and analyzed using Fourier transform infrared (IR) spectroscopy, X-ray scattering, and differential scanning calorimetry. The ASDs were exposed to accelerated thermal-oxidative conditions using a pressurized oxygen headspace (120 °C for 1 day) and high temperatures at atmospheric pressure (60-120 °C for a period of 42 days). Additionally, solution-state oxidative degradation studies showed that pure NIF degrades to a greater extent than in the presence of PVP. Electronic structure calculations were performed to understand the impact of drug-polymer intermolecular interactions on the autoxidation of drugs. While no drug degradation was observed in freshly prepared ASD samples, alkyl free radicals were detected via electron paramagnetic resonance (EPR) spectroscopy. The free radicals were found to be consumed to a greater extent by PVP K30- than PVP K90-based ASDs upon exposure to high oxygen pressures. This was consistent with the greater solid-state oxidative degradation of NIF observed in ASDs with PVP K30 than with PVP K90. As no drug recrystallization occurred during this study period, the lower glass-transition temperature and presumed greater molecular mobility of PVP K30 and its ASD as compared to the PVP K90 system appear to contribute to the greater drug degradation in PVP-K30-based ASDs. The extent and the rate of oxidative degradation were higher in the case of PVP-K30-based ASD as compared to that in PVP-K90-based ASD, and the overall degradation increased with an increase in temperature. IR spectral analysis of drug-polymer interactions supports the electronic calculations of the oxidation process. We infer that, apart from the initial free radical content, the difference in the extent of drug-polymer intermolecular interactions in ASDs and amorphous stabilization during the forced oxidation experiments contribute to the observed differences in the autoxidative reactivity of the drug in ASDs with different PVP chain lengths. Overall, the chemical degradation of NIF in ASDs with two PVP chain lengths obtained from accelerated solid-state oxidation studies was in qualitative agreement with that obtained from long-term (3 years) storage under ambient conditions. The study highlights the ability of accelerated processes to determine the oxidative degradation behavior of polymeric ASDs and suggests that the polymer chain length could factor into chemical as well as physical stability considerations.

Spectroscopic Signatures of Hydrogen-Bonding Motifs in Protonic Ionic Liquid Systems: Insights from Diethylammonium Nitrate in the Solid State

Diethylammonium nitrate, [N0 0 2 2][NO3], and its perdeuterated analogue, [N D D 2 2] [NO3], were structurally characterized and studied by infrared, Raman, and inelastic neutron scattering (INS) spectroscopy. Using these experimental data along with state-of-the-art computational materials modeling, we report unambiguous spectroscopic signatures of hydrogen-bonding interactions between the two counterions. An exhaustive assignment of the spectral features observed with each technique has been provided, and a number of distinct modes related to NH···O dynamics have been identified. We put a particular emphasis on a detailed interpretation of the high-resolution, broadband INS experiments. In particular, the INS data highlight the importance of conformational degrees of freedom within the alkyl chains, a ubiquitous feature of ionic liquid (IL) systems. These findings also enable an in-depth physicochemical understanding of protonic IL systems, a first and necessary step to the tailoring of hydrogen-bonding networks in this important class of materials.

Low rotational barriers for the most dynamically active methyl groups in the proposed antiviral drugs for treatment of SARS-CoV-2, apilimod and tetrandrine

A recent screening study highlighted a molecular compound, apilimod, for its efficacy against the SARS-CoV-2 virus, while another compound, tetrandrine, demonstrated a remarkable synergy with the benchmark antiviral drug, remdesivir. Here, we find that because of significantly reduced potential energy barriers, which also give rise to pronounced quantum effects, the rotational dynamics of the most dynamically active methyl groups in apilimod and tetrandrine are much faster than those in remdesivir. Because dynamics of methyl groups are essential for biochemical activity, screening studies based on the computed potential energy profiles may help identify promising candidates within a given class of drugs.

Periodic DFT Calculations-Review of Applications in the Pharmaceutical Sciences

In the introduction to this review the complex chemistry of solid-state pharmaceutical compounds is summarized. It is also explained why the density functional theory (DFT) periodic calculations became recently so popular in studying the solid APIs (active pharmaceutical ingredients). Further, the most popular programs enabling DFT periodic calculations are presented and compared. Subsequently, on the large number of examples, the applications of such calculations in pharmaceutical sciences are discussed. The mentioned topics include, among others, validation of the experimentally obtained crystal structures and crystal structure prediction, insight into crystallization and solvation processes, development of new polymorph synthesis ways, and formulation techniques as well as application of the periodic DFT calculations in the drug analysis.

Diversity of methyl group dynamics in felodipine: a DFT supported NMR and QENS study

Computationally-supported NMR and neutron scattering experiments were combined to provide new insights into the structure–dynamics relationship in the most stable polymorph of felodipine.

On the molecular dynamics in long-acting calcium channel blocker lacidipine: solid-state NMR, neutron scattering and periodic DFT study

A new-generation lipophilic calcium channel blocker lacidipine (LCDP) has been thoroughly explored by combining solid-state nuclear magnetic resonance (NMR) with high-flux quasi-elastic (QENS) and inelastic neutron scattering (INS) experiments.