Hybrid magnetic materials (Fe3O4–κ-carrageenan) as catalysts for the Michael addition of aldehydes to nitroalkenes

Two hybrid magnetic materials have been prepared from κ-carrageenan and Fe₃O₄ nanoparticles and tested as catalysts for the Michael addition of aldehydes to nitroalkenes. Remarkably, the material prepared from unmodified κ-carrageenan showed catalytic activity in the reaction of choice, while the individual components were inactive. This points out to a synergistic effect between the MNPs and κ-carrageenan. The second catalyst, bearing a diphenylprolinol silyl ether moiety, was also shown to promote the reaction, giving rise to the corresponding adducts in excellent ees. After the reaction is complete, the catalysts can be conveniently retrieved by simple magnetic decantation.     

Synthesis and Electronic Properties of 1,2‐Hemisquarimines and Their Encapsulation in a Cucurbit[7]uril Host

The synthesis of a new class of robust squaraine dyes, colloquially named 1,2‐hemisquarimines (1,2‐HSQiMs), through the microwave‐assisted condensation of aniline derivatives with the 1,2‐squaraine core is reported. In CH₃CN, 1,2‐HSQiMs show a broad absorption band with a high extinction coefficient and a maximum at around λ=530 nm, as well as an emission band centered at about λ=574 nm, that are pH dependent. Protonation of the imine nitrogen causes a redshift of both absorption and emission maxima, with a concomitant increase in the lifetime of the emitting excited state. Encapsulation of the chromophore into a cucurbit[7]uril host revealed fluorescence enhancement and increased photostability in water. The redox characteristics of 1,2‐HSQiMs indicate that charge injection into TiO₂ is possible; this opens up promising perspectives for their use as photosensitizers for solar energy conversion.     

Unexpected Anion Effect in the Alkoxylation of Alkynes Catalyzed by N‐Heterocyclic Carbene (NHC) Cationic Gold Complexes

The intermolecular alkoxylation of alkynes is the oldest application of cationic gold(I) catalysts; however, no systematic experimental data about the role of the anion are available. In this contribution, the role of the anion in this catalytic reaction as promoted by a N‐heterocyclic carbene‐based gold catalyst, [(NHC)AuX] (X=BARF^?, BF₄^?, OTf^?, OTs^?, TFA^?, or OAc^?) is analyzed, through a combined experimental (NMR spectroscopy) and theoretical (DFT calculation) approach. The most important factor seems to be the ability to abstract the proton from the methanol during the nucleophilic attack, and such ability is related to the anion basicity. On the other hand, too high coordination power or basicity of the anion worsens the catalytic performance by preventing alkyne coordination or by forming too much free methoxide in solution, which poisons the catalyst. The intermediate coordinating power and basicity of the OTs^? anion provides the best compromise to achieve efficient catalysis.     

Bispidines for Dual Imaging

The efficient transformation of the hexadentate bispidinol 1 into carbamate derivatives yields functional bispidines enabling convenient functionalization for targeted imaging. The BODIPY‐substituted bispidine 3 combines a coordination site for metal ions, such as radioactive ⁶⁴Cu^II, with a fluorescent unit. Product 3 was thoroughly characterized by standard analytical methods, single crystal X‐ray diffraction, radiolabeling, and photophysical analysis. The luminescence of ligand 3 was found to be strongly dependent on metal ion coordination: Cu^II quenches the BODIPY fluorescence, whereas Ni^II and Zn^II ions do not affect it. It follows that, in imaging applications with the positron emitter ⁶⁴Cu^II, residues of its origin from enriched ⁶⁴Ni and the decay products ⁶⁴Ni^II and ⁶⁴Zn^II, efficiently restore the fluorescence of the ligand. This allows for monitoring of the emitted radiation as well as the fluorescence signal. The stability of the ⁶⁴Cu^II? 3 complex is investigated by transmetalation experiments with Zn^II and Ni^II, using fluorescence and radioactivity detection, and the results confirm the high stability of ⁶⁴Cu^II? 3 . In addition, metal complexes of ligand 3 with the lanthanide ions Tb^III, Eu^III, and Nd^III are shown to exhibit emission of the BODIPY ligand and the lanthanide ion, thus enabling dual emission detection.     

Light‐Driven Organocatalysis Using Inexpensive,Nontoxic Bi2O3 as the Photocatalyst

The development of enantioselective catalytic processes that make use of sunlight as the energy source and nontoxic, affordable materials as catalysts represents one of the new and rapidly evolving areas in chemical research. The direct asymmetric α‐alkylation of aldehydes with α‐bromocarbonyl compounds can be successfully achieved by combining bismuth‐based materials as low‐band‐gap photocatalysts with the second‐generation MacMillan imidazolidinone as the chiral catalyst and simulated sunlight as a low‐cost and clean energy source. This reaction also proceeded with high efficiency when the reaction vial was exposed to the morning sunlight on a clear September day in Tarragona, Spain.     

On the Electrochemical Deposition and Dissolution of Divalent Metal Ions

The deposition of Cu²⁺ and Zn²⁺ from aqueous solution has been investigated by a combination of classical molecular dynamics, density functional theory, and a theory developed by the authors. For both cases, the reaction proceeds through two one‐electron steps. The monovalent ions can get close to the electrode surface without losing hydration energy, while the divalent ions, which have a stronger solvation sheath, cannot. The 4s orbital of Cu interacts strongly with the sp band and more weakly with the d band of the copper surface, while the Zn 4s orbital couples only to the sp band of Zn. At the equilibrium potential for the overall reaction, the energy of the intermediate Cu⁺ ion is only a little higher than that of the divalent ion, so that the first electron transfer can occur in an outer‐sphere mode. In contrast, the energy of the Zn⁺ ion lies too high for a simple outer‐sphere reaction to be favorable; in accord with experimental data this suggests that this step is affected by anions.     

Thorough investigation of the oxygen heterocyclic fraction of lime (Citrus aurantifolia (Christm.) Swingle) juice

Reversed‐phase‐HPLC analysis by means of superficially porous silica particle columns (fused‐core) was applied to the investigation of flavonoids, coumarins, and psoralens in lime juice samples. Hesperidin (367.0 ± 16.0 ppm) and eriocitrin (148.0 ± 7.9 ppm) were the most abundant flavonoids. Fifteen coumarins and furocoumarins were determined, including bergamottin (29.6 ± 1.1 ppm), 5‐geranyloxy‐7‐methoxycoumarin (16.5 ± 0.6 ppm), and oxypeucedanin hydrate (9.9 ± 0.5 ppm) as predominant compounds. These molecules are today well known for their beneficial effects on human health. As a consequence, the present study, beyond investigating for the first time the chemical composition of lime juice, highlights also its health‐promoting qualities, due to its content of flavonoids and coumarins.     

Biotransformation with whole microbial systems in a continuous flow reactor: resolution of (RS)-flurbiprofen using Aspergillus oryzae by direct esterification with ethanol in organic solvent

Cell-bound lipases of dry mycelium of Aspergillus oryzae were used in organic solvent for the resolution of racemic flurbiprofen by direct esterification with ethanol in a flow-chemistry reactor. Under flow conditions a significant reduction of the reaction time and an increase of the enantioselectivity were achieved compared to the batch mode. Moreover, the process was implemented by adding an in-line purification step integrated with the racemization of the unreacted flurbiprofen directly into a polymer-supported resin.     

New 9,10‐Secosteroids from Biotransformations of Hyodeoxycholic Acid with Rhodococcus spp.

The biotransformations of hyodeoxycholic acid with various Rhodococcus spp. are reported. Some strains (i.e., Rhodococcus zopfii, Rhodococcus ruber, and Rhodococcus aetherivorans) are able to partially degrade the side chain at C(17) to afford 6α‐hydroxy‐3‐oxo‐23,24‐dinor‐5β‐cholan‐22‐oic acid ( 2 ; 23%) and 6α‐hydroxy‐3‐oxo‐23,24‐dinorchol‐1,4‐dien‐22‐oic acid ( 3 ; 23–30%), together with two new 9,10‐secosteroids 4 and 5 (10–45%), still bearing the partial side chain at C(17) and adopting an intramolecular hemiacetal form. In addition, the 9,10‐secosteroid 5 showed an unprecedented C(4)‐hydroxylation. The new secosteroids were fully characterized by MS, IR, NMR, and 2D‐NMR analyses.