Israel Journal of Chemistry最新文献

Helmut Schwarz is a great scientist and a statesman who has made important fundamental contributions to chemistry as a science, and to the globalization of chemistry when he served as the Vice President of the German Research Foundation and subsequently as the President of the Alexander von Humboldt (AvH) Foundation.

Rovibrationally resolved spectra of the N_j=2₂, K_a=0←1 transition and of the N_j=2₃, K_a=0←0 and K_a=1←0 transitions of the hydrogen-bonded (HF)₂ have been measured in the near infrared range near 1.3 μm by cw-diode laser cavity ring-down spectroscopy in a pulsed supersonic slit jet expansion. The spectroscopic assignment and analysis provided an insight into the dynamics of these highly-excited vibrational states, in particular concerning the predissociation of the hydrogen bond and the tunneling process of the hydrogen bond switching. Together with our previously analyzed spectra of the N_j=2₁ and N_j=2₂ components, the mode-specific dynamics in all three components of this triad can now be compared. In the N=2 triad, the HF-stretching vibration is excited by two quanta with similar excitation energy, but the quanta are distributed in three different ways, which has a distinct influence on the dynamics. The observed band centers and tunneling splittings are in agreement with our recent calculations on the (HF)₂ potential energy hypersurface SO-3, resolving the long-standing discussion about the symmetry ordering of polyad levels in this overtone region. The results are also discussed in relation to the general questions of non-statistical reaction dynamics of polyatomic molecules and clusters and in relation to quasi-adiabatic channel above barrier tunneling.

Pincer ligand complexes, which appeared nearly five decades ago, have provided a valuable platform for the study of fundamental chemical processes and the development of efficient catalysts for many chemical transformations. These complexes have usually contained transition metal atoms or ions, and their respective pincer ligands have often featured phosphine donor groups, which strongly coordinate to the metal center and allow its steric and electronic properties to be fine-tuned. The increasing need to develop cost-effective and sustainable catalytic processes has driven the search for main-group metals as alternatives to commonly-used transition metals. In this review, we show that despite the inherent mismatch between phosphines, which are soft Lewis bases, and main-group metal ions, which are hard Lewis acids, a series of well-defined phosphine-based pincer complexes containing Li(I), Na(I), K(I), Mg(II), Ca(II), Zn(II) and Al(III) have been reported, which have proven to be active catalysts for industrially-relevant transformations.

Nickel-catalyzed cross-electrophile coupling (XEC) is an efficient method to form carbon-carbon bonds and has become an important tool for building complex molecules. While XEC has most often used stoichiometric metal reductants, these transformations can also be driven electrochemically. Electrochemical XEC (eXEC) is attractive because it can increase the greenness of XEC and this potential has resulted in numerous advances in recent years. The focus of this review is on electrochemical, Ni-catalyzed carbon-carbon bond forming reactions reported since 2010 and is categorized by the type of anodic half reaction: sacrificial anode, sacrificial reductant, and convergent paired electrolysis. The key developments are highlighted and the need for more scalable options is discussed.

An “OFF/ON” electric current switching protocol was developed as a new strategy for one-pot organic synthesis. Suzuki-Miyaura coupling of 2-bromopyridines with arylboronic acids in an electrochemical cell was performed without applying an electric current, and subsequently, the Pd-catalyzed electrochemical C−H bromination was conducted using the already-present Pd catalyst to obtain 2-(2-bromoaryl)pyridines as products. The one-pot synthesis of bromoarenes can also be achieved without adding an external Br source in the second step. Furthermore, an OFF/ON/OFF two-times switching protocol also realized the formation of an N-containing teraryl derivative.

A novel metal- and oxidant-free electrooxidative selenylamination of o-aminophenacetylenes with diselenides for achieving 3-selenylindoles has been developed with moderate to excellent yield. The reaction proceeded smoothly with a broad substrate scope and highly functional group tolerance. The synthetic practicality of this innovative approach was demonstrated by its easy scalability. Moreover, mechanistic studies revealed that an in-situ generated selenium cation might be the key intermediate for the electrochemical selenocyclization process.

Infections with multidrug-resistant Gram-negative bacteria constitute a silent pandemic threat that is increasing globally. A major technical and scientific hurdle hampering the development of efficient antibiotics against Gram-negative species is the low permeability of their outer membrane that prevents the entry of most small molecules into the cells. This can be overcome by targeting active iron transport systems of the pathogens in a Trojan-Horse strategy that makes use of drug-loaded artificial siderophores. While we utilized catechols as iron-binding motifs in previous work, this study reports the design, synthesis and characterization of siderophores with a DOTAM scaffold that was substituted with three hydroxamate arms allowing for a hexacoordination of iron. Their iron-chelating capabilities were shown colorimetrically, and the ability of compound 1 to deliver iron into Escherichia coli in a chelation-specific manner was proven by a growth recovery assay. A covalent siderophore-ciprofloxacin conjugate exerted antibiotic effects against E. coli, albeit it was less potent than the free drug. The study qualifies artificial DOTAM siderophores with hydroxamate binders as scaffolds for bacterial Trojan Horses. This contribution for honoring my mentor Helmut Schwarz echoes two motifs of my work with him: Hydroxylamin, the topic of my first paper ever, and the fascinating properties of iron ions, studied in the gas phase during my Ph.D. Thesis, became a core subject of our current chemical biology research on antiinfectives.

The functional roles of structured RNAs in the regulation of biological processes, and hence RNA's potential as an effective therapeutic target, have only recently been appreciated. Robust and high-throughput methods that identify potent RNA ligands are critical to the development of chemical probes and therapeutics. DNA-encoded libraries (DEL) technology has emerged as a powerful tool for protein ligand discovery, and its ability to generate large, custom-tailored, and novel chemical space offers unprecedented opportunities to discover the rules of RNA ligand design. In this review, we discuss the basic principles of DEL selection, current progress on the application of DEL to RNA targets, and the outlook of targeting RNA by DEL.

Self-folding cavitands represent the quintessential form of bioinspired synthetic receptors, featuring deep hydrophobic cavities that engage in host-guest chemistry reminiscent of that operating in biomolecules. Although remarkable proof-of-concept applications have been reported, the narrow and rigid spaces of the legacy resorcin[4]arene derived hosts constitute a liability towards the development of specific applications in catalysis, sensing or sequestration. While notable efforts to expand the size of the cavities have been reported, the development of confined spaces reproducing the highly adaptable nature of biological receptors is a largely unaddressed issue. This review summarizes the development of a new family of calix[5]arene derived self-folding cavitands displaying enhanced induced fit and conformational selection phenomena. Our approach capitalizes on hydrogen bonding preorganization rather than the covalent restriction approaches customary of conventional supramolecular chemistry.