Intermolecular π-π Stacking Interactions Made Visible

Manganese-Catalyzed Enantioselective Dearomative Epoxidation of Naphthalenes with Aqueous Hydrogen Peroxide

Arenes are abundantly occurring molecules of significant interest as versatile starting materials in organic reactions. Typically, oxidation of arenes yields planar molecules such as phenols and quinones. However, several iron dependent oxygenases can disrupt the aromaticity of arenes through oxidation and introduce C(sp3)─O stereogenic centers, resulting in precious enantioenriched epoxide or diol products. Emulating this enzymatic behavior with synthetic catalysts has met little success until now. Herein we describe a catalytic chemo- and enantioselective dearomative epoxidation of naphthalenes. The singular chemo- and enantioselectivity features of the reaction critically rely on a manganese catalyst that combines electron donating groups and steric demand on the ligand and activates hydrogen peroxide under mild conditions and short reaction times. Assisted with an N-protected amino acid, this catalyst epoxidizes a range of naphthalenes providing chemically versatile diepoxides in moderate to good yields and high levels of enantioselectivity. Straightforward elaboration gives diverse access to densely functionalized 3D structurally rich oxygenated molecules. The reaction constitutes a paradigmatical example of expedient access to stereochemically rich, valuable oxygenated molecules from readily available feedstocks, enabled by highly reactive yet selective biologically inspired oxidation catalysts.

A Disila[2]ferrocenophane with a Bridging 9,9'-Bi-9H-9-Silafluorene Moiety

A disila[2]ferrocenophane bearing a 9,9'-bi-9H-9-silafluorene (9-silafluorene dimer) moiety as a bridging unit was synthesized and isolated as a stable crystalline compound. Disila[2]ferrocenophane 1, newly obtained in this study, has been characterized by spectroscopic analyses, single crystal X-ray diffraction (SC-XRD) analysis, and electrochemical measurements. It was found that the obtained disila[2]ferrocenophane was reduced by a reducing agent to generate the corresponding 1,1'-ferrocenediyl-bis(silylanion) via the reductive Si-Si σ-bond cleavage. The trapping reactions of the 1,1'-ferrocenediyl-bis(silylanion) thus generated with electrophiles have also been attempted.

Different Stacking Types in a Single Hybrid Cocrystal System: π···π- and π-Hole-Based Organic-Inorganic Planar Assemblies

The planar bis-chelated complex [Pd(N∩O)2] (1; N∩O = 4-MeC5H3NNC(O)NMe2) exhibits two distinct stacking modes with electron-deficient aromatics: π···π stacking with hexafluorobenzene (C6F6) versus charge-transfer π-hole interactions with 1,2,4,5-tetracyanobenzene (TCB). Cocrystallization of the complex with C6F6 or TCB yields cocrystals 1·3(C6F6) and 1·2TCB, respectively, which display different colors and stacking patterns despite similar structural motifs. Comprehensive analysis using X-ray diffraction, combined with quantum theory of atoms-in-molecules (QTAIM), an independent gradient model based on Hirshfeld partition (IGMH), extended transition state natural orbital for chemical valence theory with charge displacement function (ETS-NOCV/CDF), many-body interaction analysis, and symmetry-adapted perturbation theory (SAPT), reveals fundamentally different interaction mechanisms. In 1·3(C6F6), the stacking is primarily governed by intermolecular polarization without significant charge transfer, with dispersion forces contributing approximately 70% of the attractive energy. In contrast, 1·2TCB exhibits pronounced charge transfer (35 me) and significant inductive components alongside dispersion forces, characteristic of π-hole interactions. This dichotomy in stacking behavior provides new insights into the nature of organic-inorganic planar assemblies and demonstrates that seemingly similar structural patterns can arise from distinctly different combinations of noncovalent forces, which is essential for rational crystal engineering of hybrid materials.

Influence of π-π interactions on organic photocatalytic materials and their performance

Currently, organic photocatalyst-based photocatalysis has garnered significant attention as an environmentally friendly and sustainable reaction system due to the preferable structural flexibility and adjustable optoelectronic features of organic photocatalysts. In addition, π-π interactions, as one of the common non-bonded interactions, play an important role in the structure and property adjustments of organic photocatalysts due to their unique advantages in modulating the electronic structure, facilitating charge migration, and influencing interfacial reactions. However, studies summarizing the relationship between the π-π interactions of organic photocatalysts and their photocatalytic performance are still rare. Therefore, in this review, we introduced the types of π-π interactions, characterization techniques, and different types of organic photocatalytic materials. Then, the influence of π-π interactions on photocatalysis and the modification strategies of π-π interactions were summarized. Finally, we discussed their influence on photocatalytic performance in different photocatalytic systems and analyzed the challenges and prospects associated with harnessing π-π interactions in photocatalysis. The review provides a clear map for understanding π-π interaction formation mechanism and its application in organic photocatalysts, offering useful guidance for researchers in this field.

Upcycling Humins via Esterification Reactions of Hydroxyl Groups: From Functional Powders to PLA Foams and Compatibilized Blends

The valorization of humins side streams from bio-refineries holds significant economic and sustainability potential. One plausible strategy involves using them as building blocks to create new materials. However, humins pose conceptual challenges in their natural state due to their high viscosity, processing difficulties, and temperature sensitivity. This article presents a synthetic strategy for modifying humins properties to make them thermally stable and processable. Employing a sequence of esterification reactions and varying the reagent steric length, we showcase the selective transformation of humins into thermally-stable fine powders and low-viscosity liquids. We extend this approach by reacting humins with polyesters such as polylactic acids and polycaprolactone. In particular, we detail a one-pot single-step synthesis of micro-phase separated compatibilized blends of polylactic acid and humins capped with the polylactic acid arms. Processed via solution-casting, the obtained materials behave as high-strength thermoplastic elastomers having uniform foam morphologies and material characteristics superior to the pure polylactic acid. By varying the content of D-enantiomers, we demonstrate an additional possibility of manipulating the cellular structures of the foams. Finally, we provide a solution to product circularity by reporting a dissolution recycling method.

Small Molecule Compound DHPA Screened by Computer-Aided Drug Design and Molecular Dynamics Simulation Inhibits Neuroblastoma Cell Proliferation by Targeting TrkB

Neuroblastoma (NB) is a rare and malignant pediatric solid tumor. Due to its heterogeneity, it poses significant challenges for treatment, resulting in a high mortality rate. This study aimed to identify new therapeutic drugs by modeling the TrkB receptor from PDB 4AT5 and conducting virtual screening of compounds from the YaTCM database (containing 47,696 compounds derived from 6220 Traditional Chinese Medicines). The screening utilized the E-pharmacophore approach to select compounds with potential binding affinity to TrkB. The binding abilities of these compounds were tested through molecular dynamics simulations, stretch dynamics simulations, and US simulations. Among the top 11 optimized hit compounds, DHPA and 3″-demethylhexahydrocurcumin are prominent. Further simulations reveal that they form stable receptor-ligand binary complexes with TrkB. In subsequent in vitro cell experiments, 3″-demethylhexahydrocurcumin is eliminated due to its high IC50 for killing NB cells. Low concentrations of DHPA can significantly kill NB cells. Additionally, DHPA can inhibit the expression of TrkB, the activation of TrkB's downstream signaling pathways, and affect the thermal stability of TrkB protein and its response to streptase protease degradation. DHPA may be a potential TrkB inhibitor.

Chiral Spirophosphoric-Acid-Catalyzed Divergent Vinylogous Mannich and aza-Friedel-Crafts Reactions of 2-Methoxyfuran

The first enantioselective vinylogous Mannich reaction is developed using 2-methoxyfuran under chiral spirophosphoric acid catalysis. The strategy involves 4-isoxazoline derivatives as cyclic ketimine surrogates and provides γ-butenolide scaffolds (up to 97% ee and >20:1 dr). The mechanistic investigations suggest that an in situ generated water molecule plays a crucial role in delivering γ-butenolide, while the use of molecular sieves delivers aza-Friedel-Crafts products. The synthetic utility of γ-butenolide is shown toward obtaining piperidone skeleton via a lactone-lactam rearrangement.

A Rapid 3-Day Excipient Screening Methodology and its Application in Identifying Chemical Stabilizers for Solid Formulations with Mixed Mechanisms of Degradation

This study outlines a practical approach for assessing chemical instability by heating the drug-excipient binary mixtures or multi-excipient formulations at 75°C for 3 days before characterization. Differentiating itself from other excipient compatibility methods, our methodology necessitates a saturated aqueous slurry rather than arbitrarily fixed water content. This allows bulk and surface water in the excipient to contribute to drug degradation. The synergistic impact of surface water and elevated temperature expedites degradation kinetics, resulting in accelerated data generation. Among excipient compatibility methods available, our method is quantitative and merges with traditionally used methodologies. The devised nomograph enables extrapolation of shelf life at 20°C from experimental data obtained at 75°C. This methodology also helped identify stabilizers for the drug NVS-1 where traditional excipient compatibility programs had failed. Incorporation of monovalent salts, such as sodium/potassium chloride and sodium bicarbonate at 5% w/w, significantly enhanced the chemical stability of NVS-1, ensuring stable tablet formulations. Our hypothesis posits that stabilization is due to increased ionic strength in the slurry, which stabilizes an induced dipole within the polar NVS-1 drug. Additionally, the presence of ions in the moisture layer is anticipated to stabilize π-π stacking of two planar aromatic NVS-1 molecules. The expedited generation of experimental data allowed the identification of inorganic salts to supplement a standard excipient compatibility screening panel. Considering the economic implications of stability testing methodologies in effort, cost, and duration, a faster turnaround in chemical stability data enhances formulation selection. This ultimately facilitates the development of drug formulations with greater efficiency without delays.

Hydrogen-Bonding Motifs in Adducts of Allylamine with the 10 Simplest n-Alcohols: Single-Crystal X-ray Diffraction Studies and Computational Analysis

In this paper, we analyzed the homologous series of 10 allylamine adducts with n-alcohols from methanol to decanol. These are the first adduct structures containing aliphatic n-alcohols and an aliphatic amine as co-formers. While all of the ingredients are liquids under ambient conditions, the phases were synthesized with the use of the in situ crystallization technique assisted by IR laser-focused radiation at atmospheric pressure. The structures were characterized by single-crystal X-ray diffraction. All of the phases contain the amine and alcohol in a 1:1 ratio. The architecture of the structures, based on hydrogen-bonding interactions between NH₂ and OH moieties, depends on the size of the alcohol and changes in a systematic way. The three smallest alcohol adducts contain centrosymmetric layers of molecules of the L4(4)8(8) type. The next four alcohol adducts have the T4(2) topology. The structures with the biggest alcohols contain non-centrosymmetric L6(6) layers. The structural investigations were supported by periodic DFT calculations at the B3LYP/pobTZVP level. The cohesive and adhesive energies made up of layer (E _lbe) and ribbon (E _rbe) binding energies were used to predict which type of architecture can be formed. The thermal stabilities of the adducts correlate with the melting points of the co-forming alcohols, with no evident relation to the adduct architecture.

What Goes in Must Come out: The Story of Uric Acid

Birds and reptiles convert waste ammonia into uric acid, while mammals excrete urea, with only small amounts of uric acid ending up in urine. This column explores the varying roles of uric acid and important calcium and sodium salts, and introduces π-stacking interactions in solid-state structures.

DFT and IsoStar Analyses to Assess the Utility of σ- and π-Hole Interactions for Crystal Engineering

The interpretation of 36 charge neutral 'contact pairs' from the IsoStar database was supported by DFT calculations of model molecules 1-12, and bimolecular adducts thereof. The 'central groups' are σ-hole donors (H2 O and aromatic C-I), π-hole donors (R-C(O)Me, R-NO2 and R-C6 F5 ) and for comparison R-C6 H5 (R=any group or atom). The 'contact groups' are hydrogen bond donors X-H (X=N, O, S, or R2 C, or R3 C) and lone-pair containing fragments (R3 C-F, R-C≡N and R2 C=O). Nearly all the IsoStar distributions follow expectations based on the electrostatic potential of the 'central-' and 'contact group'. Interaction energies (ΔEBSSE ) are dominated by electrostatics (particularly between two polarized molecules) or dispersion (especially in case of large contact area). Orbital interactions never dominate, but could be significant (∼30 %) and of the n/π→σ*/π* kind. The largest degree of directionality in the IsoStar plots was typically observed for adducts more stable than ΔEBSSE ≈-4 kcal⋅mol-1 , which can be seen as a benchmark-value for the utility of an interaction in crystal engineering. This benchmark could be met with all the σ- and π-hole donors studied.