Is Iron the New Ruthenium?

Ruthenium complexes with polypyridine ligands are very popular choices for applications in photophysics and photochemistry, for example, in lighting, sensing, solar cells, and photoredox catalysis. There is a long-standing interest in replacing ruthenium with iron because ruthenium is rare and expensive, whereas iron is comparatively abundant and cheap. However, it is very difficult to obtain iron complexes with an electronic structure similar to that of ruthenium(II) polypyridines. The latter typically have a long-lived excited state with pronounced charge-transfer character between the ruthenium metal and ligands. These metal-to-ligand charge-transfer (MLCT) excited states can be luminescent, with typical lifetimes in the range of 100 to 1000 ns, and the electrochemical properties are drastically altered during this time. These properties make ruthenium(II) polypyridine complexes so well suited for the abovementioned applications. In iron(II) complexes, the MLCT states can be deactivated extremely rapidly (ca. 50 fs) by energetically lower lying metal-centered excited states. Luminescence is then no longer emitted, and the MLCT lifetimes become much too short for most applications. Recently, there has been substantial progress on extending the lifetimes of MLCT states in iron(II) complexes, and the first examples of luminescent iron complexes have been reported. Interestingly, these are iron(III) complexes with a completely different electronic structure than that of commonly targeted iron(II) compounds, and this could mark the beginning of a paradigm change in research into photoactive earth-abundant metal complexes. After outlining some of the fundamental challenges, key strategies used so far to enhance the photophysical and photochemical properties of iron complexes are discussed and recent conceptual breakthroughs are highlighted in this invited Concept article.     

Calixthiacrown:A New Multidentate Ligand for Platinum Metal

CalixarenesareafamilyofcyclicoligmerspreparedfromfOrmaldehydeandpara-substitutedphenolsviacycliccondensationunderalkalineconditions.Itwassuggestedthatthecalixarenescanbecountedasthethirdhostmoleculeorthethirdgenerationofsupramolecules,aftercrownethersandcyclodextrinst,,,j.TbeycanbeusedaspIatformsorbuildingblockstoconstructaseriesofcompoundsbavingpreorganizedstructures.Whencalixareneswerebridgedbypolyoxyetbylenecbainintra-orintermolecularyly,cal-.ixcrownswereobtained.Someofthelatterexhibitedou…     

Is Cyanide Really a Strong‐Field Ligand?

Iron man or weakling? Ligand‐field strengths are conveniently expressed by the empirical spectrochemical series. Although cyanide has been deeply entrenched as a strong‐field ligand, a couple of recent examples cast doubt toward the position of this ligand, namely the high‐spin (S=2) states of [Cr^II(CN)₅]^3? and [Fe^II(tpp)(CN)]^?. tpp=meso‐tetraphenylporphinate.

     

Is the Bis(μ-oxo)dicopper Core Capable of Hydroxylating an Arene?

Direct attack of the bis(μ-oxo)dicopper core on an arene appears feasible in tyrosinase and model complexes on the basis of studies of new [Cu^III₂(μ-O)₂]²⁺ compounds supported by bidentate imine/amine ligands. In the first demonstration of such reactivity for a bis(μ-oxo)dicopper core, decomposition of these intermediates caused hydroxylation of a pendant phenyl ring [Eq. (a)] in a reaction analogous to that catalyzed by tyrosinase.     

Combinatorial Chemistry in Heterogeneous Catalysis: A New Scientific Approach or “the King's New Clothes”?

The spectacular success in materials science of the application of combinatorial chemistry has raised the hope that it may eventually lead to a new scientific approach to catalyst development. This method is, within the constraints of heterogeneous catalysis, merely a potentially efficient tool to be used in rational catalyst development and should not be considered an independent novel strategy towards rational catalyst design.     

The Determination of the Protonation Constants of A New Macrocyclic Dinucleating Ligand, BDBPH

One of our current interests focuses on the design and synthesis of polyaza macrocyclic ligands, the determination of their protonation constants, and the stabilities of corresponding metal complexes. Two polyazadiphenol macrocycles, R(babp)2(dfc)21 and [24]RBPyBC2, one octaazamacrocycle, BPBD3,4, and several hexaaza macrocyclic ligands, BFBD5, BMXD6, and OBISDIEN7, have been reported recently. We have also reported the synthesis of a new dinucleating 24-membered hexaazadiphenol macr…     

Tramadol—A True Natural Product?

We have independently investigated the source of tramadol, a synthetic analgesic largely used for treating moderate to severe pain in humans, recently found in the roots of the Cameroonian medicinal plant, Nauclea latifolia. We found tramadol and its three major mammalian metabolites (O‐desmethyltramadol, N‐desmethyltramadol, and 4‐hydroxycyclohexyltramadol) in the roots of N. latifolia and five other plant species, and also in soil and local water bodies only in the Far North region of Cameroon. The off‐label administration of tramadol to cattle in this region leads to cross‐contamination of the soil and water through feces and urine containing parent tramadol as well as tramadol metabolites produced in the animals. These compounds can then be absorbed by the plant roots and also leached into the local water supplies. The presence of tramadol in roots is, thus, due to an anthropogenic contamination with the synthetic compound.     

Tramadol—A True Natural Product?

We have independently investigated the source of tramadol, a synthetic analgesic largely used for treating moderate to severe pain in humans, recently found in the roots of the Cameroonian medicinal plant, Nauclea latifolia. We found tramadol and its three major mammalian metabolites (O‐desmethyltramadol, N‐desmethyltramadol, and 4‐hydroxycyclohexyltramadol) in the roots of N. latifolia and five other plant species, and also in soil and local water bodies only in the Far North region of Cameroon. The off‐label administration of tramadol to cattle in this region leads to cross‐contamination of the soil and water through feces and urine containing parent tramadol as well as tramadol metabolites produced in the animals. These compounds can then be absorbed by the plant roots and also leached into the local water supplies. The presence of tramadol in roots is, thus, due to an anthropogenic contamination with the synthetic compound.     

What Can We Learn from Molecular Recognition in Protein–Ligand Complexes for the Design of New Drugs?

The understanding of noncovalent interactions in protein–ligand complexes is essential in modern biochemistry and should contribute toward the discovery of new drugs. In the present review, we summarize recent work aimed at a better understanding of the physical nature of molecular recognition in protein–ligand complexes and also at the development and application of new computational tools that exploit our current knowledge on structural and energetic aspects of protein–ligand interactions in the design of novel ligands. These approaches are based on the exponentially growing amount of information about the geometry of protein structures and the properties of small organic molecules exposed to a structured molecular environment. The various contributions that determine the binding affinity of ligands toward a particular receptor are discussed. Their putative binding site conformations are analyzed, and some predictions are attempted. The similarity of ligands is examined with respect to their recognition properties. This information is used to understand and propose binding modes. In addition, an overview of the existing methods for the design and selection of novel protein ligands is given.     

A New Phase in the Binary Iron Nitrogen System?—The Prediction of Iron Pernitride,FeN2

Among numerous different AB₂ structures with the hypothetical composition FeN₂, the structures lying lowest in energy have been determined by a series of density‐functional electronic‐structure calculations. The most likely FeN₂ phase crystallizing in the space group R$\bar 3Among numerous different AB(2) structures with the hypothetical composition FeN(2), the structures lying lowest in energy have been determined by a series of density-functional electronic-structure calculations. The most likely FeN(2) phase crystallizing in the space group R3m must be considered an iron pernitride incorporating binuclear N-N units (d=1.275??) with an anionic charge of 2-. This high-pressure magnetic phase with a bulk modulus of about 192?GPa and an iron saturation moment of approximately 1.68?μ(B) should already form at a pressure of 17?GPa at an assumed reaction temperature of 1000?K. Besides bonding Fe-N interactions, antibonding N-N and Fe-Fe interactions exist in the crystal structure.