Albrechtsenslot7499

Heterometallic cooperativity is an emerging strategy to elevate polymerisation catalyst performance. Here, we report the first heterotrimetallic Na/Zn2 and K/Zn2 complexes supported by a ProPhenol ligand, which deliver "best of both" in cyclic ester ring-opening polymerisation, combining the outstanding activity (Na/K) and good control (Zn2) of homometallic analogues. Detailed NMR studies and density-functional theory calculations suggest that the Na/Zn2 and K/Zn2 complexes retain their heterometallic structures in the solution-state. To the best of our knowledge, the K/Zn2 analogue is the most active heterometallic catalyst reported for rac-lactide polymerisation (k obs = 1.7 × 10-2 s-1), giving activities five times faster than the Na/Zn2 complex. These versatile catalysts also display outstanding performance in ε-caprolatone and δ-valerolactone ring-opening polymerisation. These studies provide underpinning methodologies for future heterometallic polymerisation catalyst design, both in cyclic ester polymerisation and other ring-opening (co)polymerisation reactions.An important form of biological sulfur is sulfane sulfur, or S0, which is found in polysulfide and persulfide compounds as well as in elemental sulfur. Sulfane sulfur, often in the form of S8, functions as a key energy source in the metabolic processes of thermophilic Archaean organisms found in sulfur-rich environments and can be metabolized both aerobically and anaerobically by different archaeons. Despite this importance, S8 has a low solubility in water (∼19 nM), raising questions of how it can be made chemically accessible in complex environments. Motivated by prior crystallographic data showing S8 binding to hydrophobic motifs in filamentous glycoproteins from the sulfur reducing Staphylothermus marinus anaerobe, we demonstrate that simple macrocyclic hydrophobic motifs, such as 2-hydroxypropyl β-cyclodextrin (2HPβ), are sufficient to solubilize S8 at concentrations up to 2.0 ± 0.2 mM in aqueous solution. We demonstrate that the solubilized S8 can be reduced with the common reductant tris(2-carboxyethyl)phosphine (TCEP) and reacts with thiols to generate H2S. The thiol-mediated conversion of 2HPβ/S8 to H2S ranges from 80% to quantitative efficiency for Cys and glutathione (GSH). Moreover, we demonstrate that 2HPβ can catalyze the Cys-mediated reduction of S8 to H2S in water. Adding to the biological relevance of the developed systems, we demonstrate that treatment of Raw 264.7 macrophage cells with the 2HPβ/S8 complex prior to LPS stimulation decreases NO2 - levels, which is consistent with known activities of bioavailable H2S and sulfane sulfur. Taken together, these investigations provide a new strategy for delivering H2S and sulfane sulfur in complex systems and more importantly provide new insights into the chemical accessibility and storage of S0 and S8 in biological environments.An alternative description is provided for the previously reported novel tetranuclear cadmium carbonyl compound, [Cd(CO)3(C6H3Cl)]4. Specifically, consideration of single crystal X-ray diffraction data indicates that the compound is better formulated as the rhenium compound, [Re(CO)3(C4N2H3S)]4. Furthermore, density functional theory calculations predict that, if it were to exist, [Cd(CO)3(C6H3Cl)]4 would have a very different structure to that reported. Stattic While it is well known that X-ray diffraction may not reliably distinguish between atoms of similar atomic number (e.g. N/C and Cl/S), it is not generally recognized that two atoms with very different atomic numbers could be misassigned. The misidentification of two elements as diverse as Re and Cd (ΔZ = 27) is unexpected and serves as an important caveat for structure determinations.Understanding how metallodrugs interact with their protein targets is of vital importance for uncovering their molecular mode of actions as well as overall pharmacological/toxicological profiles, which in turn facilitates the development of novel metallodrugs. Silver has been used as an antimicrobial agent since antiquity, yet there is limited knowledge about silver-binding proteins. Given the multiple dispersed cysteine residues and histidine-methionine pairs, Escherichia coli malate dehydrogenase (EcMDH) represents an excellent model to investigate silver coordination chemistry as well as its targeting sites in enzymes. We show by systematic biochemical characterizations that silver ions (Ag+) bind EcMDH at multiple sites including three cysteine-containing sites. By X-ray crystallography, we unravel the binding preference of Ag+ to multiple binding sites in EcMDH, i.e., Cys113 > Cys251 > Cys109 > Met227. Silver exhibits preferences to the donor atoms and residues in the order of S > N > O and Cys > Met > His > Lys > Val, respectively, in EcMDH. For the first time, we report the coordination of silver to a lysine in proteins. Besides, we also observed argentophilic interactions (Ag⋯Ag, 2.7 to 3.3 Å) between two silver ions coordinating to one thiolate. Combined with site-directed mutagenesis and an enzymatic activity test, we unveil that the binding of Ag+ to the site IV (His177-Ag-Met227 site) plays a vital role in Ag+-mediated MDH inactivation. This work stands as the first unusual and explicit study of silver binding preference to multiple binding sites in its authentic protein target at the atomic resolution. These findings enrich our knowledge on the biocoordination chemistry of silver(i), which in turn facilitates the prediction of the unknown silver-binding proteins and extends the pharmaceutical potentials of metal-based drugs.Non-luminescent, isostructural crystals of [(C6H11NC)2Au](EF6)·C6H6 (E = As, Sb) lose benzene upon standing in air to produce green luminescent (E = As) or blue luminescent (E = Sb) powders. Previous studies have shown that the two-coordinate cation, [(C6H11NC)2Au]+, self-associates to form luminescent crystals that contain linear or nearly linear chains of cations and display unusual polymorphic, vapochromic, and/or thermochromic properties. Here, we report the formation of non-luminescent crystalline salts in which individual [(C6H11NC)2Au]+ ions are isolated from one another. In [(C6H11NC)2Au](BArF24) ((BArF24)- is tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) each cation is surrounded by two anions that prohibit any close approach of the gold ions. Crystallization of [(C6H11NC)2Au](EF6) (E = As or Sb, but not P) from benzene solution produces colorless, non-emissive crystals of the solvates [(C6H11NC)2Au](EF6)·C6H6. These two solvates are isostructural and contain columns in which cations and benzene molecules alternate.