A series of 2:1 fluorinated arylboronic ester adducts with 4,4′-bipyridine sustained by N→B dative bonds have been synthesized. The degree of fluorination in the arylboronic esters derived from catechol is shown to modulate the molecular conformation of the coordinated boronic ester moieties and the intermolecular interactions by means of C−H•••F and F•••F contacts that sustain the crystal lattices. The adduct derived from the catechol ester of 2,4-difluorophenylboronic acid was chosen to examine the formation of inclusion complexes with a large number of aromatic guests, affording solvates, cocrystals, and a cocrystal solvate. Six different crystal structure types with 1:1, 1:2, and 1:2:2 N→B adduct−guest ratios were observed, whose supramolecular organization is strongly influenced by the formation of sandwich-type complexes between the host and guest molecules. The host−guest interactions involve π•••π interactions with the bipyridine linkers and additional contacts with the catecholate and Baryl F substituents, indicating a large flexibility of the N→B adducts to adapt to the guest stereochemistry. The versatility of the crystallization system was employed to isolate o-xylene from an equimolar mixture of o-, m-, and p-xylene.

The combination of one dipyridyl linker [1,2-di(4-pyridyl)ethylene (DPE), 1,2-di(4-pyridyl)ethane (DPEt), or 4,4′-azopyridine (DPA)] with two molecules of arylboronate ester 1 produced dinuclear Lewis-type N→B adducts that can act as acyclic host for polycyclic aromatic hydrocarbons (PAHs) in the solid state. Nine crystalline solids of composition PAH@adduct (i.e., one PAH per adduct) were obtained from solutions containing a single PAH. On the basis of the single-crystal X-ray diffraction analysis of the compound ANT@A1 (ANT = anthracene; A1 = adduct being composed of DPE and two boronate esters 1), the PAH inclusion selectivity is related to a size-fitting adaptation to an octaedral-shaped pocket assembled by CH-π interactions between fragments of the diamine and the arylboronate ester 1. The resulting reversible organic clathrates can perform "catch and release" cycles of PAHs such as pyrene and can sequester selectively PAHs from mixtures in solution.T he molecular recognition of polycyclic aromatic hydrocarbons (PAHs) is a challenging issue given the variety of sizes, shapes, and properties of these widespread materials. 1 PAHs are among the most intensively studied pollutants in the environmental analysis of air, water, food, and solid-waste samples. Methods for quantitative separation and detection of PAHs often rely on traditional chromatographic and solventextraction protocols. 2 A well-established supramolecular approach to bind PAHs in solution consists of the use of polycationic macrocycles and cages derived from extended viologens, which are assembled covalently 3 or through metal coordination. 4 The association constants of these host−guest complexes in water and polar solvents range between 10 1 and 10 6 M −1 , and a significant number of X-ray crystal structures of such complexes has been reported. Yet these elegant supramolecular receptors were made in multistep synthetic procedures 3 or involved costly transition metals. 4 Thus, it is still a demanding task to develop simple methods to selectively detect PAHs, and also to be able to recover them quantitatively as a single (or multiple) PAH from mixtures in solution. 1,2 In the past decade, various research groups have comprehensively explored the interaction of aromatic amines with boronate esters and boroxines to provide a broad variety of discrete and polymeric materials, such as macrocycles, 5 nanostructures, 6 coordination polymers, 7 and gels. 8 Hence, supramolecular assembly based on dative N→B interactions is recognized as a useful strategy for the generation of complex systems, and given its thermodynamic stability (−11 to −38 kJmol −1 ) 6,7 and kinetic lability in polar coordinating solvents, the central N→B binding motif can be compared to a typical noncovalent interaction. The potential of this approach is well exemplified by the prismatic organic cages assembled via N→B bonds that were able to encapsulate triphenylene or coronene in the solid state. 6c These previous reports have also evidenced that simple arylmonoboronate esters ...

The thermodynamic stability of 1 : 1 and 2 : 1 boron–nitrogen (B←N) adducts formed between aromatic boronic esters with mono‐ and diamines was studied in solution by NMR and UV‐vis spectroscopy with association energies (ΔG°) ranging from −11 to −28 kJ mol−1. The effect of different substituents in the boronic ester, the nature of the diamine linker, and the effect of the solvent was explored. Stable 2 : 1 B←N adducts with diamines such as 1,3‐diaminopropane were produced in solutions of hydrogen‐bonding acceptor solvents (acetonitrile and ethyl acetate), which can be isolated in the solid state as crystalline solvates, whereas the use of noncoordinating solvents such as 1,2‐dichloroethane afforded mainly 1 : 1 B←N adducts. In suitable combinations, aromatic bis‐pyridyl diamines produced stable 2 : 1 B←N adducts that were isolated either as solvent‐free solids, solvates, or cocrystals. In these crystalline forms, double‐tweezer hosts were observed with an exceptional syn/anti conformational guest‐adaptability driven by simultaneous donor‐acceptor and C−H⋅⋅⋅π interactions in the tweezer cavities, resembling preorganized covalent tweezer hosts. Interestingly, cocrystals with electron‐rich guests such as tetrathiafulvalene and pyrene showed non‐centrosymmetric crystal lattices with infinite π‐stacked donor–acceptor columns.

Purpose: To prepare some 2-amino-4-(p-substituted phenyl)-oxazole derivatives and to evaluate their in vitro antiprotozoal activity against Giardia lamblia and Trichomonas vaginalis. Methods: The 2-amino-4-(p-substituted phenyl)-oxazoles (a-g) were synthesized by microwave (MW) irradiation of mixtures of p-substituted 2-bromoacetophenones and urea in dimethylformamide (DMF). All compounds were identified by 1 H and 13 C nuclear magnetic resonance (NMR) spectroscopy and lowand high-resolution mass spectrometry (HRMS). NMR assignments were made based on heteronuclear single quantum coherence (HSQC) and heteronuclear multiple bond correlation (HMBC) experiments. Each synthesized compound's melting point was determined. Antiprotozoal activity against Giardia intestinalis and Trichomonas vaginalis was quantified using a rigorous and sensitive subculture method. The commercial drug, metronidazole, was used as positive control. The 50 % inhibitory concentration (IC50) of the antiprotozoal agents for each protozoa was determined. Results: Seven 2-amino-4-(p-substituted phenyl)-oxazoles (a-g) were synthesized. The most active compounds against G. lamblia was 2-amino-4-(p-benzoyloxyphenyl)-oxazole (3d) with an IC50 of 1.17 µM, while compound 3e (2-amino-4-(p-bromophenyl)-oxazole) showed the highest anti-trichomonal activity (IC50, 1.89 µM). Conclusion: The in vitro antigiardial activity of 2-amino-4-(p-benzoyloxyphenyl) oxazole was higher than that exhibited by metronidazole; however, it is necessary increase the number of synthetic derivatives in order to be able to determine their structure-activity relationship.

Refractory aromatic sulfur compounds present in gasoline, diesel, and jet fuels cause serious environmental problems and must be removed to minimize the emissions of SO x , according to environmental regulations worldwide. Herein, we present a novel approach for the removal of organosulfur compounds from model liquid fuel solutions employing a nonporous host crystalline material (A1) that undergoes transformation into cocrystals with aromatic sulfur compounds like benzothiophene (BT) and dibenzothiophene (DBT) (i.e., A1⊃BT and A1⊃DBT). In experiments using a single component in cyclohexane solutions, crystalline A1 reached a quantitative uptake of DBT after 12 h at 25 °C with equimolar or slightly increased molar ratios of DBT over A1 (e.g., 1.45 ± 0.05 mmol of S/g of A1, which is equivalent to 267.3 ± 9.3 mg of DBT/g of A1 at C 0 = 3000 ppmwS). The crystalline material A1 can be recycled from cocrystal A1⊃DBT by a two-step process: (i) the generation of the solid A1⊃toluene upon extraction of DBT in toluene and (ii) the subsequent thermal treatment at 150 °C for desolvation to recover microcrystalline A1; after four recycling processes, the uptake capacity of A1 is maintained at 97.5%. In competitive experiments using a five-component equimolar cyclohexane solution containing BT, DBT, 4,6-dimethyldibenzothiophene (DMDBT), fluorene (FLUO), and naphthalene (NAPH), the uptake efficiency of A1 after 12 h at 25 °C followed the trend: DBT > FLUO > NAPH > BT > DMDBT. The selective uptake of DBT in these model fuel solutions is explained by matching of the π-electron rich guest with π-electron deficient diamine linkers and concomitant CH−π interactions within the enclosed cavities of the double-tweezer B←N host A1, as exhibited in the X-ray crystal structure. Size fitting is important for guest selectivity because attempts to isolate cocrystals with DMDBT were unsuccessful. Crystal-to-cocrystal is a solution mediated phase transformation that competes favorably in the removal of DBT with several examples of high-surface nano/microporous materials and composites used in batch adsorption experiments, and A1 can be recycled without compromising efficiency. Thus, crystal-to-cocrystal transformation emerges as a remarkable methodology for the quantitative removal of aromatic organosulfur compounds from liquid fuels because it can be extended to many other aromatic fuel contaminants by using the appropriate host molecule to cocrystallize with it.