Chemistry - A European Journal最新文献

We have developed a family of dinuclear complexes using 2,7-disubstituted 1,8-naphthalenediol ligands that bind by molecular recognition to two neighboring phosphate diesters of the DNA backbone with the dinuclear CuII and NiII complexes exhibiting a severe cytotoxicity for human cancer cells. To increase the binding affinity, we intended to synthesize the corresponding dinuclear FeIII complex. Surprisingly, we obtained a tetranuclear FeIII perylene-based complex instead of the expected dinuclear FeIII naphthalene-based complex. In order to establish a rational and reproducible synthesis, we carefully analyzed this reaction. This revealed a multistep oxidative cascade reaction including the pre-coordination of FeII ions in the N3-binding pockets, the Lewis-acid assisted MOM-deprotection of the pre-ligand by the pre-oriented FeII ions, two oxidative aromatic C-C coupling reactions, oxidation of the perylene-based backbone and of FeII to FeIII. The careful analysis of bond lengths, HOMA indices (harmonic oscillation model of aromaticity), FTIR and UV-Vis-NIR spectra supported by DFT calculations reveals the presence of an aromatic 18-electron oxidized perylenequinone ligand backbone. In summary, a multistep cascade reaction involving in total a 10-electron oxidation has been established for the straight-forward synthesis of an unprecedented perylenequinone-based ligand system.

The structural variability and chemical stability of metal phosphonates under harsh conditions are attractive attributes that have drawn considerable attention in recent years. As the needs for more sustainable solutions rise, the demand for novel and tolerant materials also increases. Thus, herein we report, for the first time, the synthesis of a novel diphosphonic organic linker named pyrazole diphenyl phosphonate (PZDP), envisioning the fabrication of durable metal phosphonates. In view of this, a series of M-PZDP materials (M = Ca, Sr, Ba, Zn and Co) were synthesized employing either solvothermal or hydrothermal methods. The crystal structures of the Ca, Sr, Zn, and Co derivatives were determined revealing a 2D-pillared architecture. Zn-PZDP is an anionic framework with dimethylammonium cations. The Co-PZDP compound was tested as a heterogeneous catalyst in olefin epoxidation employing molecular oxygen.

We present a series of six hypervalent bismuth complexes Bi(R1PDPR2)X bearing ligands characterized by the pyridine-2,6-bis(pyrrolide) (PDP) structural motif. While bismuth holds considerable potential for facilitating efficient intersystem crossing (ISC), reports on phosphorescent molecular bismuth complexes are still scarce and mostly based on systems that exhibit inter‑ or intraligand charge transfer character of their optical excitations. Herein, the UV/vis absorptive, luminescent, and electrochemical properties of complexes Bi(R1PDPR2)X are explored, where the substituents R1 and R2, as well as the halide ligand X are varied. These compounds are characterized by an intense HOMO®LUMO transition of mixed ligand-to-metal charge transfer (LMCT) and interligand charge transfer (LL'CT) character, as shown by time-dependent density functional theory (TD-DFT) calculations. At 77 K in a 2-MeTHF matrix, these compounds exhibit red, long-lived phosphorescence with lifetimes ranging from 671 to 20 µs. Cyclic voltammetry measurements and TD-DFT calculations show that the substituents influence HOMO and LUMO energies to almost equal extent, resulting in nearly constant emission wavelengths throughout this series. Single-crystal X-ray diffraction studies of four of the six complexes exemplify the inherent Lewis acidity of the coordinated Bi3+ ion, in spite of its hypervalency.

Cysteine (Cys) detection is recognized as an essential element in this investigation due to the critical function of Cys in several physiological processes in living organisms. A new NIR fluorescent probe SNC-Cys has been synthesized by incorporating a five-membered malononitrile derivatized ring as an electron withdrawing group, and a methacryloyl group detection moiety for cysteine. After adding Cys, SNC-Cys shows an emission of 654 nm and further works as a "Turn-on" probe via ICT photomechanism. SNC-Cys has high sensitivity and selectivity for Cys (LOD = 0.46 µM) and can discriminate it from other closely related amino acids, molecules with structural similarity, and in some cases very close functional group likeness. Thus, these results allow the effective imaging of Cys in living A549 cells which indicates good cell permeability and high applicability in live cell imaging. This study anticipates that SNC-Cys could be an aid in the detection of Cys-relevant diseases.

A Pd(II)-catalyzed non-template synthesis of furo[2,3-b]pyrrolo[2,3-d]pyridines from b-ketodinitriles and buta-1,3-diynes has been accomplished via dual annulative cyclization. The participation of both the nitrile (-CN) groups led to the concurrent construction of three heterocycles viz. furan, pyrrole, and pyridine forming C-C, C=C, C-O, C-N, and C=N bonds in one pot. The synthetic utility of the protocol was further demonstrated through a few post-synthetic manipulations.

Two novel 1,10-phenanthroline-2,9-diamide ligands were constructed based on 2-phenylpyrrolidine and obtained as pure diastereomers. These ligands demonstrated advanced properties in liquid-liquid extraction tests. They revealed high efficiency of americium(III) extraction alongside with the record values of selectivity in the separation of americium from light lanthanides from strongly acidic media. An abrupt increase of extraction efficiency when moving along the lanthanide series from lanthanum to lutetium was observed. The examination of the extraction behavior of pure diastereomeric forms revealed noticeable differences in their selectivity while maintaining the overall extraction trend. The explanation of the discovered patterns was elucidated by a comprehensive study of the ability of the ligands to bind lanthanide nitrates in solutions. All the data collected (UV-vis and NMR titration, X-ray analysis of resulting complexes, solvation numbers estimation) were supported by quantum chemical calculation. These data clearly indicated that in case of light lanthanides the formation of 1:1 complexes is most preferable. In the same time, complexes with heavy lanthanides, such as ytterbium and lutetium, exist as ionic pairs which may consist of [L2M]z+ cations counterbalanced by metallates anions, which may result in formation of unusual composition species L2M2 or even L4M5 clusters.

The absolute and relative configurations of a macrocyclic natural product bearing multiple chirality have a crucial influence on its physical and biological properties. Nevertheless, their preparation with full stereocontrol remains largely unexplored in synthetic community. Here, we show a stereodivergent macrocyclization under dynamic chiral confinement in which the stepwise chirality switching of a chiral space directs complete stereocontrol. To confine a substrate in a dynamic chiral space, we used a chiral capsule enclosing a substrate which is collectively switchable in the chirality in response to external stimuli, but their conformations are firmly fixed by subsequent self-assembly. The consecutive chirality switching enables the confined reactions of an enclosed achiral substrate to sequentially install diverse chirality on a macrocycle product with full stereocontrol in a single pot operation, thus changing only a sequence of physical stimuli enables access to a remarkable stereodivergence in a macrocyclization process.

Oxo-graphene nanoribbons (oxo-GNRs) can be prepared by the oxidative unzipping of single-walled carbon nanotubes. We present an orthogonal functionalization method for the functionalization of the rims and the π-surface, respectively, what is only possible due to the high rim portion in oxo-GNRs. Thus, in particular X-ray photoelectron spectroscopy could be used to trace reaction to detect marker atoms included in addends. We propose that the reported orthogonal functionalization strategy can also be applied on other oxo-functionalized carbon materials, such as carbon dots, or reduced graphene oxide flakes.

Nitrides represent a promising class of materials for a variety of applications. However, bulk synthesis remains a challenging task due to the stability of the N2 molecule. In this study, we introduce a simple and scalable approach for synthesizing nitride bulk materials. Moderate reaction temperatures are achieved by using reactive starting materials, slow and continuous mixing of the starting materials, and by dissipating heat generated during the reaction. The impact on the synthesis of using different starting materials as nitrogen source and the influence of a flux were examined. γ-Sn3N4 was selected as the model compound. The synthesis of pure γ-Sn3N4 bulk material on a large scale has still been a challenge, although a few synthesis methods were already described in the literature. Here we synthesized γ-Sn3N4 by metathesis reaction of argon-diluted SnCl4 with Li3N, Mg3N2 or Ca3N2 as nitrogen sources. Products were characterized by powder X-ray diffraction, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, dynamic flash combustion analysis, hot gas extraction analysis, X-ray photoelectron spectroscopy, Mössbauer spectroscopy and X-ray absorption and emission spectroscopy. Additionally, single-crystal diffraction data of γ-Sn3N4, previously unavailable, were successfully collected.

The use of VIV and CuII spins to design weakly coupled and dissymmetric spin systems has been examined. Such systems were synthesized using porphyrin-based complexes, with external coordination sites allowing for the formation of dimers via a PdII linker ion. Continuous-wave (CW) Electron Paramagnetic Resonance (EPR) spectroscopy allowed the unequivocal magnetic characterization of the mononuclear precursors V and Cu. The porphyrin dimer VPdCu presented a broad and overlapped spectrum that was more pronounced than for the previously reported VPdV, hinting at the effect of weak interspin interactions between dissimilar spins. Pulsed EPR experiments on V, VPdV and VPdCu samples diluted in a diamagnetic matrix confirmed that this complication is also present in the Field-Swept Echo-Detected (FSED) spectra of the heterometallic VPdCu system. Despite the strongly overlapped field-swept spectra, spin nutation experiments revealed two distinct oscillations in the case of VPdCu, which are assigned to transitions with different spin characters. Remarkably, coherence is retained above liquid nitrogen temperatures for all complexes, in particular up to 295 K for V and VPdV and 150 K for VPdCu.