Hydrogen-Mediated Noncovalent Interactions in Solids: What Can NMR Crystallography Tell About?

Resolving the Chemical Formula of Nesquehonite via NMR Crystallography, DFT Computation, and Complementary Neutron Diffraction

Nesquehonite is a magnesium carbonate mineral relevant to carbon sequestration envisioned for carbon capture and storage of CO₂ . Its chemical formula remains controversial today, assigned as either a hydrated magnesium carbonate [MgCO₃  ⋅ 3H₂ O], or a hydroxy- hydrated- magnesium bicarbonate [Mg(HCO₃ )OH ⋅ 2H₂ O]. The resolution of this controversy is central to understanding this material's thermodynamic, phase, and chemical behavior. In an NMR crystallography study, using rotational-echo double-resonance ¹³ C{¹ H} (REDOR), ¹³ C-¹ H distances are determined with precision, and the combination of ¹³ C static NMR lineshapes and density functional theory (DFT) calculations are used to model different H atomic coordinates. [MgCO₃  ⋅ 3H₂ O] is found to be accurate, and evidence from neutron powder diffraction bolsters these assignments. Refined H positions can help understand how H-bonding stabilizes this structure against dehydration to MgCO₃ . More broadly, these results illustrate the power of NMR crystallography as a technique for resolving questions where X-ray diffraction is inconclusive.

Synthesis of a Pyridone-Based Phthalimide Fleximer and Its Characterization and Supramolecular Property Evaluation

In this study, a novel pyridone-based phthalimide fleximer, that is, ethyl 5-cyano-6-(3-(1,3-dioxoisoindolin-2-yl)propoxy)-4-(3-methoxyphenyl)-2-methylnicotinate, was synthesized, and its structure was established by the single-crystal X-ray diffraction method. The supramolecular self-assembly of the titled compound through noncovalent interactions was then investigated thoroughly. The titled compound crystallized with two symmetry-independent molecules (A and B, Z' = 2). In agreement with experimental observations, our density functional theory calculations also showed that the titled compound has a flexible motif and can occur in various conformations, including molecules A and B. The investigation of the supramolecular framework revealed that the molecules are notably bound by the nonclassical C-H···O and C-H···N hydrogen bonds and C-H···π interactions. Hirshfeld surface analysis was carried out to quantify the various intermolecular interactions. The dual anti-inflammatory activity of the tilted compound was also explored by molecular docking in the active sites of 5-LOX and COX-2 receptors, which revealed good binding affinities of -9.0 and -8.6 kcal/mol, respectively.

Co-Crystals of Etravirine by Mechanochemical Activation

The co-crystals formation of etravirine with three carboxylic acids was investigated. New co-crystals of etravirine with adipic acid, benzoic acid, and 4-hydroxybenzoic acid have been synthesized by wet milling of ingredients for 120 min. The novelty of these solid forms was first evidenced by powder X-ray diffraction. Their different morphology was evidenced by SEM microscopy. Spectroscopic analyses (FT-IR, MAS-NMR, and XPS) highlighted the hydrogen bonds between etravirine and co-formers, as a result of the solid-state reaction of the ingredients by wet milling. Thermal analyses pointed out that the milling process caused in co-crystals a reduction in the fusion enthalpy and the melting temperature, compared to the values obtained for etravirine. These co-crystals are stable up to four months on storage under extreme conditions, excepting the co-crystal with benzoic acid which begins to transform into a polymorph of etravirine after 30 days. The UV absorption spectra of the samples tested in three simulated physiological media with pH values of 6, 6.3, and 7 have evidenced the conformation change of etravirine due to hydrogen bonds between etravirine and carboxylic acids.

Polyaniline/Biopolymer Composite Systems for Humidity Sensor Applications: A Review

The development of polyaniline (PANI)/biomaterial composites as humidity sensor materials represents an emerging area of advanced materials with promising applications. The increasing attention to biopolymer materials as desiccants for humidity sensor components can be explained by their sustainability and propensity to absorb water. This review represents a literature survey, covering the last decade, which is focused on the interrelationship between the core properties and moisture responsiveness of multicomponent polymer/biomaterial composites. This contribution provides an overview of humidity-sensing materials and the corresponding sensors that emphasize the resistive (impedance) type of PANI devices. The key physicochemical properties that affect moisture sensitivity include the following: swelling, water vapor adsorption capacity, porosity, electrical conductivity, and enthalpies of adsorption and vaporization. Some key features of humidity-sensing materials involve the response time, recovery time, and hysteresis error. This work presents a discussion on various types of humidity-responsive composite materials that contain PANI and biopolymers, such as cellulose, chitosan and structurally related systems, along with a brief overview of carbonaceous and ceramic materials. The effect of additive components, such as polyvinyl alcohol (PVA), for film fabrication and their adsorption properties are also discussed. The mechanisms of hydration and proton transfer, as well as the relationship with conductivity is discussed. The literature survey on hydration reveals that the textural properties (surface area and pore structure) of a material, along with the hydrophile-lipophile balance (HLB) play a crucial role. The role of HLB is important in PANI/biopolymer materials for understanding hydration phenomena and hydrophobic effects. Fundamental aspects of hydration studies that are relevant to humidity sensor materials are reviewed. The experimental design of humidity sensor materials is described, and their relevant physicochemical characterization methods are covered, along with some perspectives on future directions in research on PANI-based humidity sensors.

Nanoformulations of Ursolic Acid: A Modern Natural Anticancer Molecule

Background: Ursolic acid (UA) is a natural pentacyclic triterpene derived from fruit, herb, and other plants. UA can act on molecular targets of various signaling pathways, inhibit the growth of cancer cells, promote cycle stagnation, and induce apoptosis, thereby exerting anticancer activity. However, its poor water-solubility, low intestinal mucosal absorption, and low bioavailability restrict its clinical application. In order to overcome these deficiencies, nanotechnology, has been applied to the pharmacological study of UA.

Objective: In this review, we focused on the absorption, distribution, and elimination pharmacokinetics of UA in vivo, as well as on the research progress in various UA nanoformulations, in the hope of providing reference information for the research on the anticancer activity of UA.

Methods: Relevant research articles on Pubmed and Web of Science in recent years were searched selectively by using the keywords and subheadings, and were summarized systematically.

Key finding: The improvement of the antitumor ability of the UA nanoformulations is mainly due to the improvement of the bioavailability and the enhancement of the targeting ability of the UA molecules. UA nanoformulations can even be combined with computational imaging technology for monitoring or diagnosis.

Conclusion: Currently, a variety of UA nanoformulations, such as micelles, liposomes, and nanoparticles, which can increase the solubility and bioactivity of UA, while promoting the accumulation of UA in tumor tissues, have been prepared. Although the research of UA in the nanofield has made great progress, there is still a long way to go before the clinical application of UA nanoformulations.