Tetrahedron clusters serving as a platform for foam-like structure design.

There are a number of exceptional examples indicating the unique position of tetrahedral symmetry in the vast landscape of different spatial organization pathways which can be sampled by matter. This work shows that the design and analysis of relatively simple tetrahedron clusters can lead to the formulation of a new type of dendritic structure together with unique periodic frameworks resembling clathrates and foams. A simple sequential protocol leading from regular tetrahedron clusters to more complex structural motifs can be employed to determine interesting repetitive building units. Accordingly, four different hierarchical superstructures are introduced, in which the dominant population of nodes is based on tetrahedral symmetry. The introduced architectures could be of particular interest for the field of regenerative medicine and metamaterial engineering.

Experimental and theoretical insights into the structure and molecular dynamics of 2,3,3',4'-tetramethoxy-trans-stilbene - a chemopreventive agent.

The methoxy analogue of a trans-stilbene compound - 2,3,3',4'-tetramethoxy-trans-stilbene - was selected to characterize its crystallographic structure, intermolecular interactions and molecular dynamics. The sample was studied using single-crystal X-ray diffraction (XRD), infrared spectroscopy (FT-IR), liquid and solid-state 1H and 13C nuclear magnetic resonance (NMR) and quasielastic neutron scattering (QENS). The compound crystallized in the orthorhombic Pbca space group. The experimental methods were supported by theoretical calculations, density functional theory (plane-wave DFT) and molecular dynamics simulations (MD) methods. Combining several experimental and simulation techniques allowed the detailed analysis of molecular reorientations and provided a consistent picture of the molecular dynamics. The internal molecular mobility of the studied compound can be associated with the reorientational dynamics of four methyl groups. Interestingly, a large diversity of the energy barriers was observed - one methyl group reoriented across low activation barriers (∼3 kJ mol-1), while three methyl groups exhibited a high activation energy (10-14 kJ mol-1) and they are characterised by very different correlation times differing by almost two orders of magnitude at room temperature. The intramolecular interactions mainly influence the activation barriers.

An Investigation of the Sol-Gel Transition of Chitosan Lactate and Chitosan Chloride Solutions via Rheological and NMR Studies.

In recent years, intensive research has been carried out on the use of hydrogels obtained from natural polymers, mainly chitosan. These products are increasingly replacing solutions based on synthetic materials in medicine. This publication presents the results of studies on the sol-gel transition of chitosan solutions as the base material for the preparation of thermosensitive hydrogels for potential applications in tissue engineering. The measurements were carried out for systems consisting of chitosan lactate and chitosan chloride solutions using ß-glycerol phosphate disodium salt pentahydrate and uridine 5'-monophosphate disodium salt as the cross-linking agents. The sol-gel transition point of the solutions was determined based on the rheological measurements in the cone-plate configuration of the rotational rheometer and experiments performed using the method of nuclear magnetic resonance. The obtained results showed a significant influence of the cross-linking agent on the course of the sol-gel transition of chitosan salt solutions, and the systems that consisted of chitosan lactate seemed to be especially interesting for biomedical applications.

Molecular Dynamics and Structure of Poly(Methyl Methacrylate) Chains Grafted from Barium Titanate Nanoparticles.

Core-shell nanocomposites comprising barium titanate, BaTiO3 (BTO), and poly(methyl methacrylate) (PMMA) chains grafted from its surface with varied grafting densities were prepared. BTO nanocrystals are high-k inorganic materials, and the obtained nanocomposites exhibit enhanced dielectric permittivity, as compared to neat PMMA, and a relatively low level of loss tangent in a wide range of frequencies. The impact of the molecular dynamics, structure, and interactions of the BTO surface on the polymer chains was investigated. The nanocomposites were characterized by broadband dielectric and vibrational spectroscopies (IR and Raman), transmission electron microscopy, differential scanning calorimetry, and nuclear magnetic resonance. The presence of ceramic nanoparticles in core-shell composites slowed down the segmental dynamic of PMMA chains, increased glass transition temperature, and concurrently increased the thermal stability of the organic part. It was also evidenced that, in addition to segmental dynamics, local ß relaxation was affected. The grafting density influenced the self-organization and interactions within the PMMA phase, affecting the organization on a smaller size scale of polymeric chains. This was explained by the interaction of the exposed surface of nanoparticles with polymer chains.

Combinations of Piperine with Hydroxypropyl-ß-Cyclodextrin as a Multifunctional System.

Piperine is an alkaloid that has extensive pharmacological activity and impacts other active substances bioavailability due to inhibition of CYP450 enzymes, stimulation of amino acid transporters and P-glycoprotein inhibition. Low solubility and the associated low bioavailability of piperine limit its potential. The combination of piperine with 2-hydroxypropyl-ß-cyclodextrin (HP-ß-CD) causes a significant increase in its solubility and, consequently, an increase in permeability through gastrointestinal tract membranes and the blood-brain barrier. X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) were used to characterize interactions between piperine and HP-ß-CD. The observed physicochemical changes should be combined with the process of piperine and CD system formation. Importantly, with an increase in solubility and permeability of piperine as a result of interaction with CD, it was proven to maintain its biological activity concerning the antioxidant potential (2,2-diphenyl-1-picryl-hydrazyl-hydrate assay), inhibition of enzymes essential for the inflammatory process and for neurodegenerative changes (hyaluronidase, acetylcholinesterase, butyrylcholinesterase).

Hydroxypropyl-ß-cyclodextrin as an effective carrier of curcumin - piperine nutraceutical system with improved enzyme inhibition properties.

The nutraceutical system of curcumin-piperine in 2-hydroxypropyl-ß-cyclodextrin was prepared by using the kneading technique. Interactions between the components of the system were defined by X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR). Application of hydroxypropyl-ß-cyclodextrin as a carrier-solubiliser improved solubility of the curcumin-piperine system, its permeability through biological membranes (gastrointestinal tract, blood-brain barrier) as well as the antioxidant, antimicrobial and enzyme inhibitory activities against acetylcholinesterase and butyrylcholinesterase.

Kinetics of the thermal response of poly(N-isopropylacrylamide co methacrylic acid) hydrogel microparticles under different environmental stimuli: A time-lapse NMR study.

HYPOTHESIS: Hydrogels of N-isopropylacrylamide and methacrylic acid (P(NIPAm-co-MAA)) display pH sensitivity and complex positively charged molecules through carboxylate groups, while having a critical solution temperature at which they reduce in volume and dehydrate. We aimed to elucidate how the responsiveness of MAA to environmental changes alters PNIPAm hydrogels at the molecular level using nuclear magnetic resonance (NMR). Time-lapse NMR allows us to follow the evolution of NMR signal under a temperature stimulus, providing unique information on conformational freedom of the hydrogel polymers. EXPERIMENTS: We used time-lapse NMR to follow the evolution of the NMR signal with time over a temperature change from 25 to 40°C and to study the swelling/deswelling kinetics of P(NIPAm-co-MAA) microgels at different pH values and ionic strengths, and in the presence of positively charged molecules complexing carboxylate groups. FINDINGS: At acid pH, hydrogel collapse is favored over neutral pH, and at basic pH the carboxylates remain steadily hydrated during temperature increase. Increasing ionic strength results in a faster, more effective collapse than decreasing pH. Complexation of medium-sized molecules with several charges (spermine, spermidine) causes a faster collapse than complexation with large molecular weight poly(allylamine) hydrochloride, but similar to the collapse effected by large poly(diallyldimethylammonium) chloride. This work opens new perspectives to using time-lapse NMR to study thermoresponsive systems that respond to multiple stimuli, with particular relevance in designing hydrogels for drug delivery.

Toward Next-Generation Biohybrid Catalyst Design: Influence of Degree of Polymerization on Enzyme Activity.

Due to their capacity to conduct complex organic transformations, enzymes find extensive use in medical and industrial settings. Unfortunately, enzymes are limited by their poor stability when exposed to harsh non-native conditions. While a host of methods have been developed to stabilize enzymes in non-native conditions, recent research into the synthesis of polymer-enzyme biohybrids using reversible deactivation radical polymerization approaches has demonstrated the potential of increased enzymatic activity in both native and non-native environments. In this manuscript, we utilize the enzyme lipase, as a model system, to explore the impact that modulation of grafted polymer molecular weight has on enzyme activity in both aqueous and organic media. We studied the properties of these hybrids using both solution-phase enzyme activity methods and coarse-grain modeling to assess the impact of polymer grafting density and grafted polymer molecular weight on enzyme activity to gain a deeper insight into this understudied property of the biohybrid system.

The effect of substrate and surface plasmons on symmetry breaking at the substrate interface of the topological insulator Bi2Te3.

A pressing challenge in engineering devices with topological insulators (TIs) is that electron transport is dominated by the bulk conductance, and so dissipationless surface states account for only a small fraction of the conductance. Enhancing the surface-to-volume ratio is a common method to enhance the relative contribution of such states. In thin films with reduced thickness, the confinement results in symmetry-breaking and is critical for the experimental observation of topologically protected surface states. We employ micro-Raman and tip-enhanced Raman spectroscopy to examine three different mechanisms of symmetry breaking in Bi2Te3 TI thin films: surface plasmon generation, charge transfer, and application of a periodic strain potential. These mechanisms are facilitated by semiconducting and insulating substrates that modify the electronic and mechanical conditions at the sample surface and alter the long-range interactions between Bi2Te3 and the substrate. We confirm the symmetry breaking in Bi2Te3 via the emergence of the Raman-forbidden [Formula: see text] mode. Our results suggest that topological surface states can exist at the Bi2Te3/substrate interface, which is in a good agreement with previous theoretical results predicting the tunability of the vertical location of helical surface states in TI/substrate heterostructures.

Molecular dynamics of 1-ethyl-3-methylimidazolium triflate ionic liquid studied by 1H and 19F nuclear magnetic resonances.

The molecular dynamics of an ionic liquid (IL) composed of a 1-ethyl-3-methylimidazolium cation and a triflate (trifluoromethanesulfonate) anion, abbreviated as [Emim][TfO], were studied by NMR spectroscopy. By measuring the temperature-dependent high-field 1H and 19F spin-lattice relaxation (SLR) rates, the frequency-dependent 1H and 19F SLR dispersion curves using fast-field-cycling relaxometry, and the temperature-dependent 1H and 19F diffusion constants, and by utilizing the fact that the primary NMR-active nucleus on the Emim cation is 1H, whereas on the TfO anion it is 19F, the cationic and anionic dynamics were studied separately. A single theoretical relaxation model successfully reproduced all the experimental data of both types of resonant nuclei by fitting all the data simultaneously with the same set of fit parameters. Upon cooling, [Emim][TfO] exhibited a supercooled liquid phase between TSL = 256 K and the crystallization temperature TCr ≈ 227-222 K, as confirmed by differential scanning calorimetry (DSC) experiments. Theoretical analysis revealed that within the liquid and the supercooled liquid states of [Emim][TfO], the 1H and 19F relaxation rates are affected by both the rotational and translational diffusional processes with no discontinuous change at TSL. While the rotational diffusion is well described as an Arrhenius thermally activated process, the translational diffusion undergoes strong freezing dynamics that are well described by the Vogel-Fulcher model assuming a freezing temperature of T0 = 157 K. The existence of the supercooled liquid region in the [Emim][TfO] IL should be taken into account when using this IL for a specific application.

Molecular and Vibrational Dynamics in the Cholesterol-Lowering Agent Lovastatin: Solid-State NMR, Inelastic Neutron Scattering, and Periodic DFT Study.

Molecular and vibrational dynamics of a widely used cholesterol-lowering agent, lovastatin, have been studied by combining nuclear magnetic resonance relaxation experiments (1H NMR) with inelastic neutron scattering (INS) and periodic density functional theory modeling (plane-wave DFT). According to a complementary experimental study, lovastatin shows no phase transitions down to cryogenic conditions, while a progressive, stepwise activation of several molecular motions is observed below room temperature. The molecular packing and intermolecular forces were analyzed theoretically, supported by a 13C NMR study and further correlated with observed molecular dynamics. The NMR relaxation experiments combined with theoretical calculations disclose that molecular dynamics in solid lovastatin is related to methyl group motions and conformational disorder in the methylbutanoate fragment. This is precisely assigned and analyzed quantitatively from both experimental and theoretical perspectives. The neutron vibrational spectroscopy further corroborates that the methyl rotors have a classical nature. In addition to the intramolecular reorientations, the vibrational dynamics was analyzed with an emphasis on the low-wavenumber range. For the first time, the terahertz response of lovastatin was studied by confronting neutron and optical techniques and clearly illustrating their complementarity. The consistent picture of the molecular dynamics is provided, which may support further considerations on alternative drug formulations and the amorphization tendency in this important lipid-lowering drug.

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

Three isostructural 1,4-dihydropyridines (DHPs), namely, nifedipine, nitrendipine and nimodipine were selected to characterize their structure, intermolecular interactions and molecular dynamics. The studied samples were analyzed using powder X-ray diffraction (XRD), neutron (INS) and infrared spectroscopy (FT-IR) as well as solid-state nuclear magnetic resonance (NMR), where each technique was supported by the state-of-the-art theoretical calculations for solid-state. By combining multiple experimental techniques with advanced theoretical calculations we were able to shed light on the mutual relation between the structure, stabilizing intermolecular interactions and their spectral response. For the first time, unambiguous computationally-supported assignment of the most prominent spectral features in DHPs is presented to give a valuable support for polymorph screening and drug control. Molecular motions were interpreted in details, revealing that a dynamic reservoir of each compound is dominated by intra-molecular reorientations of methyl groups and large-amplitude oscillations in terminal chains. Our study successfully validates the realm of applicability of first-principles solid-state calculations in search of the mutual relation between the structure and spectroscopy in this important class of drugs. Such approach gives a first necessary step to gather combined structure-dynamics data on functionalized DHPs, which are of importance to better understand crystallization and binding tendency. The NMR relaxation experiments reveal that nitro groups significantly hinder the reorientation of methyl rotors and provide the first evidence of low-temperature methyl-group tunneling in DHPs, an intriguing quantum-effect which is to be further explored.

Experimental and solid-state computational study of structural and dynamic properties in the equilibrium form of temazepam.

Structural properties and rotational dynamics of methyl groups in the most stable form of temazepam were investigated by means of (13)C CP MAS NMR, quasielastic neutron scattering (QENS), and (1)H NMR spin-lattice relaxation methods. The QENS and (1)H NMR studies reveal the inequivalency of methyl groups, delivering their activation parameters. The structural properties of the system were explored in frame of periodic density functional theory (DFT) computations, giving insight into the reorientational barriers and providing understanding of the solid-state NMR results. The theoretical computations are shedding light on the intermolecular interactions along their relation with particular asymmetric structural units.