Solvent-Free Mechanosynthesis of Oligopeptides by Coupling Peptide Segments of Different Lengths - Elucidating the Role of Cesium Carbonate in Ball Mill Processes.

We report an idea for the synthesis of oligopeptides using a solvent-free ball milling approach. Our concept is inspired by block play, in which it is possible to construct different objects using segments (blocks) of different sizes and lengths. We prove that by having a library of short peptides and employing the ball mill mechanosynthesis (BMMS) method, peptides can be easily coupled to form different oligopeptides with the desired functional and biological properties. Optimizing the BMMS process we found that the best yields we obtained when TBTU and cesium carbonate were used as reagents. The role of Cs2CO3 in the coupling mechanism was followed on each stage of synthesis by 1H, 13C and 133Cs NMR employing Magic Angle Spinning (MAS) techniques. It was found that cesium carbonate acts not only as a base but is also responsible for the activation of substrates and intermediates. The unique information about the BMMS mechanism is based on the analysis of 2D NMR data. The power of BMMS is proved by the example of different peptide combinations, 2+2, 3+2, 4+2, 5+2 and 4+4. The tetra-, penta-, hexa-, hepta- and octapeptides obtained under this project were fully characterized by MS and NMR techniques.

"Crystal memory" Affects the Properties of Peptide Hydrogels - The Case of the Cyclic Tyr-Tyr dipeptide.

In this work a relationship between the crystal form and morphology and rheological properties of peptide-based hydrogels is examined. We show, that under favorable circumstances a correlation between a starting solid material and a self-assembly processes in solution can exist, leading to different properties of a resulting soft matter. This observation, together with an in-depth analysis of the influence of stereochemistry of self-assembled (ll) and (dl) Tyr-Tyr cyclic dipeptides (cYY) on the observed relationship between gelation and crystallization allowed us to gain a deeper understanding of the peptide hydrogelation processes at a molecular level, using liquid state NMR, rheological studies and scanning electron microscopy. In the course of our studies, several crystal forms of (ll)-cYY has been discovered and described in details using single crystal X-ray diffraction, as well as advanced solid state NMR, X-ray diffraction of powders, thermal analysis, FTIR, circular dichroism and crystal structure prediction (CSP) calculations. Subsequently, we found that while (ll)-cYY easily assembles into hydrogels with different properties depending on the starting solid form, (dl)-cYY always precipitated as one crystal form in the tested conditions. Molecular-level justification for this observation is given.

Laser Patterning a Graphene Layer on a Ceramic Substrate for Sensor Applications.

This paper describes a method for patterning the graphene layer and gold electrodes on a ceramic substrate using a Nd:YAG nanosecond fiber laser. The technique enables the processing of both layers and trimming of the sensor parameters. The main aim was to develop a technique for the effective and efficient shaping of both the sensory layer and the metallic electrodes. The laser shaping method is characterized by high speed and very good shape mapping, regardless of the complexity of the processing. Importantly, the technique enables the simultaneous shaping of both the graphene layer and Au electrodes in a direct process that does not require a complex and expensive masking process, and without damaging the ceramic substrate. Our results confirmed the effectiveness of the developed laser technology for shaping a graphene layer and Au electrodes. The ceramic substrate can be used in the construction of various types of sensors operating in a wide temperature range, especially the cryogenic range.

Correction: Analysis of local molecular motions of aromatic sidechains in proteins by 2D and 3D fast MAS NMR spectroscopy and quantum mechanical calculations.

Correction for 'Analysis of local molecular motions of aromatic sidechains in proteins by 2D and 3D fast MAS NMR spectroscopy and quantum mechanical calculations' by Piotr Paluch et al., Phys. Chem. Chem. Phys., 2015, 17, 28789-28801.

Analysis of local molecular motions of aromatic sidechains in proteins by 2D and 3D fast MAS NMR spectroscopy and quantum mechanical calculations.

We report a new multidimensional magic angle spinning NMR methodology, which provides an accurate and detailed probe of molecular motions occurring on timescales of nano- to microseconds, in sidechains of proteins. The approach is based on a 3D CPVC-RFDR correlation experiment recorded under fast MAS conditions (ν(R) = 62 kHz), where (13)C-(1)H CPVC dipolar lineshapes are recorded in a chemical shift resolved manner. The power of the technique is demonstrated in model tripeptide Tyr-(d)Ala-Phe and two nanocrystalline proteins, GB1 and LC8. We demonstrate that, through numerical simulations of dipolar lineshapes of aromatic sidechains, their detailed dynamic profile, i.e., the motional modes, is obtained. In GB1 and LC8 the results unequivocally indicate that a number of aromatic residues are dynamic, and using quantum mechanical calculations, we correlate the molecular motions of aromatic groups to their local environment in the crystal lattice. The approach presented here is general and can be readily extended to other biological systems.

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.

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.

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.

Study of host-guest interactions in benzodiazacoronands by means of solid state NMR spectroscopy, X-ray diffraction and quantum mechanical computations.

In this work we present solid state data for five host-guest complexes formed by N-(4,19-dioxo-2,8,15,21-tetraoxa-5,18-diazatricyclohexacosa-1(25),9(14),10,12,22(26),23-hexaen-26-yl)-benzamide (1) belonging to the group of benzodiazacoronands, achiral compounds for which chiral crystals were found (J. Kalisiak and J. Jurczak, Cryst. Growth Des., 2006, 6, 20). The X-ray structure was resolved for four of them. It was found that 1 crystallizes in P2(1)/c, P1 and P2(1)/n achiral space groups. Differentiation of molecular packing and the presence of guest molecules within the crystal lattice were analyzed with solid state NMR. An attempt was made to correlate changes in (13)C δ(ii) and (15)N δ(ii) chemical shift tensor values, obtained from analysis of spinning sidebands of 1D and 2D (2D PASS) NMR spectra, with changes in the strength of hydrogen bonding. Quantum mechanical DFT GIAO calculations of NMR shielding parameters carried out on structures with coordinates taken from XRD were employed for signals assignment and verification of structural constraints.

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).

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.

Synthesis and solid-state study of supramolecular host-guest assemblies: Bis[6-O,6-O'-(1,2:3,4-diisopropylidene-alpha-D-galactopyranosyl)thiophosphoryl] dichalcogenides.

A complementary approach for studying structural details of complex solid materials formed by symmetrical and unsymmetrical dichalcogenides, which employs both X-ray diffraction (XRD) and solid-state NMR (SS NMR), is presented. The new diagnostic technique allows reversible crystallographic space group change and very subtle distortion of host geometry to be followed during guest migration in the crystal lattice. Bis[6-O,6-O'-(1,2:3,4-diisopropylidene-alpha-D-galactopyranosyl)]thiophosphoryl selenenyl sulfide, a representative of wheel-and-axle host (WAAH) molecules, can be synthesized in the solid state by grinding and gentle heating of disulfide 1 and diselenide 2. Full characterization of disulfide 1 in the solid phase has been reported (J. Org. Chem. 1995, 60, 2549). In the current work, the synthesis and both XRD and SS NMR studies of the isostructural diselenide substrate 2 are presented. A (31)P cross polarization magic angle spinning experiment is employed to follow the progress of synthesis of selenenyl sulfide 3 in the solid state. It is concluded that selenenyl sulfide exists in equilibrium with disulfide and diselenide in a 1:1:1 ratio in both the liquid and the powdered solid. A mixture of isostructural dichalcogenides crystallized from different solvents form three-component host-guest inclusion complexes with columnar architecture. In the host-guest complex of diselenide 2 with toluene (space group C2), columns of host molecules are in parallel orientations along all the axes, whereas in the structures of diselenide 2 with propan-2-ol and propan-1-ol (space group P3 2), the columns of host molecules lay along the 3-fold symmetry axis. Thermal processes effecting structural changes in the host lattice and the kinetics of reversible guest molecule diffusion were investigated using SS NMR spectroscopy. Finally, the Se/S scrambling phenomenon and limitations in the X-ray structure refinement of organic compounds containing selenium and sulfur in chains are discussed.