Agata Jeziorna

Recent progress in solid-state NMR studies of drugs confined within drug delivery systems.

Recent progress in the application of solid-state NMR (SS NMR) spectroscopy in structural studies of active pharmaceutical ingredients (APIs) embedded in different drug carriers is detailed. This article is divided into sections. The first part reports short characterization of the nanoparticles and microparticles that can be used as drug delivery systems (DDSs). The second part shows the applicability of SS NMR to study non-steroidal anti-inflammatory drugs (NSAIDs). In this section, problems related to API-DDS interactions, morphology, local molecular dynamics, nature of inter- or intramolecular connections, and pore filling are reviewed for different drug carriers (e.g. mesoporous silica nanoparticles (MSNs), cyclodextrins, polymeric matrices and others). The third and fourth sections detail the recent applications of SS NMR for searching for antibiotics and anticancer drugs confined in zeolites, MSNs, amorphous calcium phosphate and other carriers.

Ibuprofen in mesopores of Mobil Crystalline Material 41 (MCM-41): a deeper understanding.

In this work, we compared two methods (incipient wetness and melting) for the encapsulation of ibuprofen in the pores of Mobil Crystalline Material 41 (MCM-41) through NMR (nuclear magnetic resonance) spectroscopy. (1)H NMR spectra were recorded under very fast MAS (sample spinning 60 kHz) conditions in both 1D and 2D mode (NOESY sequence). We also performed (13)C cross-polarization magic angle spinning (CP/MAS) experiments, (13)C single pulse experiments (SPE), and (1)H-(13)C HSQC HR/MAS (heteronuclear single quantum coherence high resolution) HR/MAS correlations. Evaluation of the encapsulation methods included an analysis of the filling factor of the drug into the pores. The stability of Ibu/MCM in an environment of ethanol or water vapor was tested. Our study showed that melting a mixture of Ibu and MCM is a much more efficient method of confining the drug in the pores compared to incipient wetness. The optimal experiments for the former method achieved a filling factor of approximately 60%. We concluded that the major limitation to the applicability of the incipient wetness method (filling factor ca. 20%) is the high affinity of solvent (typically ethanol) for MCM-41. We found that even ethanol vapor can remove Ibu from the pores. When a sample of Ibu/MCM was stored for a few hours in a closed vessel with ethanol vapor, Ibu was transported from the pores to the outer walls of MCM. We observed a similar phenomenon with water vapor, although this process is slower compared to the analogous procedure using ethanol. Our study clearly demonstrates that existing methods used to encapsulate drugs in mesoporous silica nanoparticles (MSNs) require reevaluation.

Synthesis of polyfunctional phosphorodithioates and structural analogues mediated by azetidinium ions and epoxides

Abstract The nucleophilic ring opening reactions of N , N- dialkyl-3-hydroxy(benzyloxy)azetidinium salts 1 and N , N -dibenzyl-2,3-epoxypropylamine 10 with anions of mono- and dithioacids of phosphorus 2 affords phosphorodithioates (and structural analogues) 3 and 11 possessing S -propyl substituents incorporating 2-hydroxy and 3-dialkylamino functionalities. A strong dependence of the stability of these compounds on structural factors is discussed.

Study of the thermal processes in molecular crystals of peptides by means of NMR crystallography

1D and 2D Very Fast Magic Angle Spinning (VF MAS) NMR experiments with sample rotation up to 55 kHz were applied to study both the dihydrate form of Tyr–(D)Ala–Phe–Gly (N-terminal sequence of opioid peptide dermorphin) and the anhydrous form, which was obtained by thermal treatment. Employing both homo-nuclear (1H–1H BABA, 13C–13C SHANGHAI) and hetero-nuclear 2D correlations (1H–13C and 1H–15N) with inverse detection, it was shown that removing water from the crystal lattice of this tetrapeptide does not destroy its subtle pseudo-cyclic structure, and its supramolecular array is preserved. The GIPAW method was employed to compute the geometry of the peptides and calculate the 13C σii principal elements of the NMR shielding tensor parameters and 1H isotropic NMR shifts. The theoretical values of 13C σii were compared with the experimental 13C δii chemical shift tensor values obtained by a 2D PASS experiment. The correlations 13C σii versus δii and 1H σiso versus δiso were used to evaluate the quality of the computational approach. With the new set of coordinates obtained by the GIPAW method, the crystal and molecular structure of the dehydrated Tyr–(D)Ala–Phe–Gly peptide that was obtained by thermal treatment was constructed. Methodology used in this project combining NMR measurements, analysis of X-ray powder diffraction data and advanced quantum mechanical calculations is known as NMR crystallography.

Computational and experimental study of reversible hydration/dehydration processes in molecular crystals of natural products – a case of catechin

When employing a complementary approach that joins theoretical (crystal structure prediction, CSP, gauge-including projector-augmented wave density functional theory, GIPAW DFT) and experimental (solid-state nuclear magnetic resonance, SSNMR) techniques, we prove that detectable changes in the water content in a crystal lattice can be monitored as a continuous or quantum process by using border values of the measurable number of water molecules in the crystal, depending on the observation probe. In the case of a 13C nucleus, which “feels” the presence of water in its nearest neighbourhood, the subtle changes in the structure of the water channel during the dehydration/rehydration process are not reflected until the water loss exceeds a certain number of molecules. Here, the dehydration of (+)-catechin 4.5-hydrate with a loss of ca. 1–1.5 and 2–2.5H2O molecules leads to microcrystalline form II (partially dehydrated) or amorphous form III, respectively. The CSP calculations for the partially dehydrated (+)-catechin (form II), as verified by experimental 1H and 13C shieldings, resulted in two similar probable crystal structures, which have 2 and 2.5 water molecules in the unit cell.

Study of the Mechanism of Thermal Chemical Processes in the Crystals of YAF Tripeptides by Means of Mass Spectrometry and Solid State NMR

Thermal reactions in two Tyr-Ala-Phe (YAF) tripeptide crystals with different molecular packing (monoclinic and hexagonal), distinct stereochemistry of central amino acid (D or L alanine) and specific arrangement of molecules in the crystal lattice (head-to-tail) were investigated. Samples were heated up to 180 °C, while the melting point for YAF crystals is above the 220 °C. Below the melting temperature, in both cases the chemical reactions leading to formation of cyclic dipeptides (YA diketopiperazine) and leaving of phenylalanine were observed. Two possible mechanisms of chemical reaction in the crystal lattice assuming intra- and/or intermolecular pathways were considered. (13)C and (15)N enriched YAF samples were employed to study of mechanism of solid state reactivity using mass spectrometry and advanced solid state NMR techniques (2D DARR (Dipolar Assisted Rotational Resonance) and 2D Double CP (Cross-Polarization) correlations).

Magic angle spinning NMR study of interaction of N-terminal sequence of dermorphin (Tyr-d-Ala-Phe-Gly) with phospholipids.

Two modifications of the Tyr-d-Ala-Phe-Gly tetrapeptide with different C-terminal groups (Tyr-d-Ala-Phe-Gly-OH 1 and Tyr-d-Ala-Phe-Gly-NH(2)2) were investigated by various nuclear magnetic resonance sequences under magic angle spinning. The structural constraints obtained from the magic angle spinning nuclear magnetic resonance measurements suggest that both peptides are aligned on the surface of the membrane and that the sandwich-like π-CH(3)-π arrangement of the pharmacophore is preserved. The influence of the chemical modification of the C-terminal residue of 1 and 2 on their interaction with phosphate group of the phospholipid in the subgel phase L(c) and the conformation of the peptides in the liquid crystalline phase L(α) are discussed. The correlation between the X-ray structure of 1 in the solid state and 1 embedded into a membrane in the L(c) phase is presented on the basis of the comparative analysis of the two-dimensional (13)C-(13)C dipolar-assisted rotational resonance cross-peaks and the (13)C isotropic chemical shifts.

Chapter Two - Recent Progress in the Solid-State NMR Studies of Short Peptides: Techniques, Structure and Dynamics

In this chapter, progress in the solid-state NMR studies of short peptides published during the last 10 years is reviewed. The chapter is divided into sections. After the preface, Section 2 presents a comprehensive introduction to the modern NMR techniques which are used in structural studies of peptides. Techniques employing fast magic-angle spinning with sample rotation over 40 kHz are highlighted. Two-dimensional homo- and heteronuclear correlation experiments with inverse detection (based on J and dipolar interactions) are discussed for spin I = 1/2 nuclei as well as for quadrupolar nuclei (I > 1/2). Section 3 reviews methodologies which are employed to analysis of molecular dynamics of peptides in the solid state. Tools for inspection of local molecular motions in different time scales such as measurements of relaxation times, chemical shift anisotropies, line-shape analysis of static spectra and heteronuclear dipolar couplings obtained by means of recoupling sequences are shortly discussed. Section 4 is devoted to problem of polymorphism and solvatomorphism. Special attention is paid to NMR study of hydrates and their solid-state transformations. In Section 5, the complementarity of theoretical (GIPAW, GIAO, ONIOM) and NMR methods in structural analysis of peptides in the solid state is reviewed. The attention is paid to the assignment problem, refinement of crystal and molecular structure for disordered peptides and correlations between theoretical and experimental shielding parameters for systems which are under fast exchange regime.

Influence of environmental humidity on organization and molecular dynamics of heteromacrocyclic assemblies.

1D and 2D NMR study, Car-Parrinello molecular dynamics, as well as classical molecular dynamics were employed to investigate three derivatives of benzodiazacoronands (achiral compounds which are able to form single crystals with a planar chirality) with intention to explain all subtle effects important during their preorganization, the step anticipating formation of crystals. The experimental study was carried out in two solvents: chloroform and DMSO either containing traces of water (commercial samples) or carefully dried over molecular sieves. Both methods revealed that environmental humidity has a dramatic influence on topology of solute-solvent interactions. Damping of the macrocycle dynamics by its diverse types of interactions with water molecules was shown by computational means. In the most spectacular experiment, we have proved that in chloroform-d during the low temperature measurements traces of water dramatically change the spectral pattern, leading to isochronous NMR signals of the AB spin system of benzodiazacoronand. The temperature of isochronous point (TIP) strongly depends on the benzodiazacoronand/water (BW) ratio. This observation opens a pathway to a new strategy based on variable temperature crystallizations and fitting of BW ratio with hope to optimize conditions for formation of chiral crystals.