Combined Experimental and Computational Investigations of Rhodium‐Catalysed CH Functionalisation of Pyrazoles with Alkenes

Detailed experimental and computational studies have been carried out on the oxidative coupling of the alkenes C₂H₃Y (Y=CO₂Me ( a ), Ph ( b ), C(O)Me ( c )) with 3‐aryl‐5‐R‐pyrazoles (R=Me ( 1 a ), Ph ( 1 b ), CF₃ ( 1 c )) using a [Rh(MeCN)₃Cp*][PF₆]₂/Cu(OAc)₂ ? H₂O catalyst system. In the reaction of methyl acrylate with 1 a , up to five products ( 2 aa – 6 aa ) were formed, including the trans monovinyl product, either complexed within a novel Cu^I dimer ( 2 aa ) or as the free species ( 3 aa ), and a divinyl species ( 6 aa ); both 3 aa and 6 aa underwent cyclisation by an aza‐Michael reaction to give fused heterocycles 4 aa and 5 aa , respectively. With styrene, only trans mono‐ and divinylation products were observed, whereas with methyl vinyl ketone, a stronger Michael acceptor, only cyclised oxidative coupling products were formed. Density functional theory calculations were performed to characterise the different migratory insertion and β‐H transfer steps implicated in the reactions of 1 a with methyl acrylate and styrene. The calculations showed a clear kinetic preference for 2,1‐insertion and the formation of trans vinyl products, consistent with the experimental results.     

Can CH⋅⋅⋅π Interactions Be Used To Design Single‐Chain Magnets?

This theoretical study suggests that CH???π stacking interactions between monomeric units can be used to design novel single‐chain magnets (SCMs), as the sign of coupling is predictable and such chains inherently yield negative axial anisotropy, a condition often difficult to achieve in conventional SCMs.     

Torands Revisited: Metal Sequestration and Self‐Assembly of Cyclo‐2,9‐tris‐1,10‐phenanthroline Hexaaza Macrocycles

A series of novel toroidal cyclo‐2,9‐tris‐1,10‐phenanthroline macrocycles with an unusual hexaaza cavity are reported. Nickel‐mediated Yamamoto aryl–aryl coupling was found to be a versatile tool for the cyclotrimerization of functionalized 1,10‐phenathroline precursors. Due to the now improved processability, both liquid‐crystalline behavior in the bulk phase and two‐dimensional self‐assembly at the molecular level could be studied, for the first time, for a torand system. The macrocycles exhibited a strong affinity for the complexation of different metal cations, as evidenced by MALDI‐TOF analysis and spectroscopic methods. Experimental results were correlated to an extensive computational study of the cyclo‐2,9‐tris‐1,10‐phenanthroline cavity and its binding mode for metal cations. Due to the combination of several interesting features, toroidal macrocycles may find future applications in the field of ion and charge transport through molecular channels, as well as for chemical sensing and molecular writing in surface‐confined monolayers under STM conditions.     

Magnetic Relaxation in Single‐Electron Single‐Ion Cerium(III) Magnets: Insights from Ab Initio Calculations

Detailed ab initio calculations were performed on two structurally different cerium(III) single‐molecule magnets (SMMs) to probe the origin of magnetic anisotropy and to understand the mechanism of magnetic relaxations. The complexes [Ce^III{Zn^II(L)}₂(MeOH)]BPh₄ ( 1 ) and [Li(dme)₃][Ce^III(cot′′)₂] ( 1 ; L=N,N,O,O‐tetradentate Schiff base ligand; 2 ; DME=dimethoxyethane, COT′′=1,4‐bis(trimethylsilyl)cyclooctatetraenyldianion), which are reported to be zero‐field and field‐induced SMMs with effective barrier heights of 21.2 and 30 K respectively, were chosen as examples. CASSCF+RASSI/SINGLE_ANISO calculations unequivocally suggest that m_J|±5/2〉 and |±1/2〉 are the ground states for complexes 1 and 2 , respectively. The origin of these differences is rooted back to the nature of the ligand field and the symmetry around the cerium(III) ions. Ab initio magnetisation blockade barriers constructed for complexes 1 and 2 expose a contrasting energy‐level pattern with significant quantum tunnelling of magnetisation between the ground state Kramers doublet in complex 2 . Calculations performed on several model complexes stress the need for a suitable ligand environment and high symmetry around the cerium(III) ions to obtain a large effective barrier.     

Study of the forced degradation behavior of prasugrel hydrochloride by liquid chromatography with mass spectrometry and liquid chromatography with NMR detection and prediction of the toxicity of the characterized degradation products

Prasugrel was subjected to forced degradation studies under conditions of hydrolysis (acid, base, and neutral), photolysis, oxidation, and thermal stress. The drug showed liability in hydrolytic as well as oxidative conditions, resulting in a total of four degradation products. In order to characterize the latter, initially mass fragmentation pathway of the drug was established with the help of mass spectrometry/time‐of‐flight, multiple stage mass spectrometry and hydrogen/deuterium exchange data. The degradation products were then separated on a C₁₈ column using a stability‐indicating volatile buffer method, which was later extended to liquid chromatography‐mass spectrometry studies. The latter highlighted that three degradation products had the same molecular mass, while one was different. To characterize all, their mass fragmentation pathways were established in the same manner as the drug. Subsequently, liquid chromatography‐nuclear magnetic resonance (NMR) spectroscopy data were collected. Proton and correlation liquid chromatography with NMR spectroscopy studies highlighted existence of diastereomeric behavior in one pair of degradation products. Lastly, toxicity prediction by computer‐assisted technology (TOPKAT) and deductive estimation of risk from existing knowledge (DEREK) software were employed to assess in silico toxicity of the characterized degradation products.     

Imprinted silica nanoparticles coated with N‐propylsilylmorpholine‐4‐carboxamide for the determination of m‐cresol in synthetic and real samples

m‐Cresol‐imprinted silica nanoparticles coated with N‐propylsilylmorpholine‐4‐carboxamide have been developed that contain specific pockets for the selective uptake of m‐cresol. Silica nanoparticles were synthesized by a sol–gel process followed by functionalization of their surface with N‐propylsilylmorpholine‐4‐carboxamide. The formation of m‐cresol‐imprinted silica nanoparticles was confirmed by UV‐Vis spectrophotometry, infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy. Electron microscopic studies revealed the formation of monodispersed imprinted silica nanoparticles with spherical shape and an average size of 83 nm. The developed nanoparticles were filled in a syringe and used for the extraction of m‐cresol from aqueous samples followed by quantification using high‐performance liquid chromatography with diode array detection. Various adsorption experiments showed that developed m‐cresol‐imprinted silica nanoparticles exhibited a high adsorption capacity and selectivity and offered a fast kinetics for rebinding m‐cresol. The chromatographic quantification was achieved using mobile phase consisting of acetonitrile/water (70:30 v/v) at an isocratic flow rate of 1.0 mL/min using a reversed‐phase C₁₈ column and detection at λ_max = 275 nm. The limits of detection and quantification were 1.86 and 22.32 ng/mL, respectively, for the developed method. The percent recoveries ranged from 96.66–103.33% in the spiked samples. This combination of this nanotechnique with molecular imprinting was proved as a reliable, sensitive and selective method for determining the target from synthetic and real samples.     

Morphological,mechanical, and in vitro cytocompatibility analysis of poly(vinyl alcohol)–silica glass hybrid scaffolds reinforced with cellulose nanocrystals

Cellulose nanocrystal-reinforced poly(vinyl alcohol)/silica glass hybrid scaffolds were fabricated using the freeze-drying method. In this study, we develop molecular-level-based hybrid scaffolds with possible bioactivity behavior by adding silica sol–gel. The results showed a highly porous structure and a significant improvement in mechanical performance (stiffness) of hybrid scaffolds with an increased content of cellulose nanocrystals followed by the addition of silica-based bioactive glass. In vitro cell study with MC3T3-E1 cells on hybrid scaffolds for 1 and 3 days revealed good cell adhesion and growth. Thus, the obtained hybrid scaffold may be a competitive candidate for bone tissue engineering applications.     

Poly(vinyl alcohol)-α-chitin composites reinforced by oil palm empty fruit bunch fiber-derived nanocellulose

Poly(vinyl alcohol)-α-chitin composite films reinforced by oil palm empty fruit bunch fiber-derived nanocellulose were prepared by casting technique. Fourier transform infrared spectroscopy analysis revealed partial miscibility between chitin and poly(vinyl alcohol) through hydrogen bonding, as supported by differential scanning calorimetry and field emission scanning electron microscopy. Tensile strength of the poly(vinyl alcohol)/chitin films increased with α-chitin content varied from 10 to 30?wt%, which was from 29.06 to 39.27?MPa. With the addition of 1?wt% nanocellulose, a maximum improvement of 57.64 and 50.66% in terms of tensile strength and Young’s modulus was achieved, respectively.