P-P Coupling and Terminal Metal-Phosphorus Intermediates.

Terminal metal-phosphorus (M-P) complexes are of significant contemporary interest as potential platforms for P-atom transfer (PAT) chemistry. Decarbonylation of metal-phosphaethynolate (M-PCO) complexes has emerged as a general synthetic approach to terminal M-P complexes. M-P complexes that are stabilized by strong M-P multiple bonds are kinetically persistent and isolable.

Crystallography Reveals Metal-Triggered Restructuring of β-Hairpins.

Metal binding to β-sheets occurs in many metalloproteins and is also implicated in the pathology of Alzheimer's disease. De novo designed metallo-β-sheets have been pursued as models and mimics of these proteins. However, no crystal structures of canonical β-sheet metallopeptides have yet been obtained, in stark contrast to many examples for ɑ-helical metallopeptides, leading to a poor understanding for their chemistry.

Hydrogen atom abstraction by a high spin [Fe=S] complex.

Iron sulfur clusters are critical to a plethora of biological processes; however, little is known about the elementary unit of these clusters, namely the [Fe=S] fragment. Here, we report the synthesis and characterization of a terminal iron sulfido complex. Despite its high spin ( = 5/2) ground state, structural, spectroscopic, and computational characterization provide evidence for iron sulfur multiple bond character.

Divalent Titanium via Reductive N-C Coupling of a Ti Nitrido with π-Acids.

The nitrido-ate complex [(PN)Ti(N){μ-K(OEt)}] (1) (PN=(N-(2-PPr-4-methylphenyl)-2,4,6-MeCH) reductively couples CO and isocyanides in the presence of DME or cryptand (Kryptofix222), to form rare, five-coordinate Ti complexes having a linear cumulene motif, [K(L)][(PN)Ti(NCE)] (E=O, L=Kryptofix222, (2); E=NAd, L=3 DME, (3); E=NBu, L=3 DME, (4); E=NAd, L=Kryptofix222, (5)). Oxidation of 2-5 with [Fc][OTf] afforded an isostructural Ti center containing a neutral cumulene, [(PN)Ti(NCE)] (E=O, (6); E=NAd (7), NBu (8)) and characterization by CW X-band EPR spectroscopy, revealed unpaired electron to be metal centric. Moreover, 1e reduction of 6 and 7 in the presence of Kryptofix222cleanly reformed corresponding discrete Ti complexes 2 and 5, which were further characterized by solution magnetization measurements and high-frequency and -field EPR (HFEPR) spectroscopy.

Electronic Structure of Three-Coordinate Fe and Co β-Diketiminate Complexes.

The β-diketiminate supporting group, [ArNCRCHCRNAr], stabilizes low coordination number complexes. Four such complexes, where R = -butyl, Ar = 2,6-diisopropylphenyl, are studied: (nacnac)ML, where M = Fe, Co and L = Cl, CH. These are denoted , , , and and have been previously reported and structurally characterized.

The Active-Site [4Fe-4S] Cluster in the Isoprenoid Biosynthesis Enzyme IspH Adopts Unexpected Redox States during Ligand Binding and Catalysis.

()-4-Hydroxy-3-methylbut-2-enyl diphosphate reductase, or IspH (formerly known as LytB), catalyzes the terminal step of the bacterial methylerythritol phosphate (MEP) pathway for isoprene synthesis. This step converts ()-4-hydroxy-3-methylbut-2-enyl diphosphate (HMBPP) into one of two possible isomeric products, either isopentenyl diphosphate (IPP) or dimethylallyl diphosphate (DMAPP). This reaction involves the removal of the C4 hydroxyl group of HMBPP and addition of two electrons.

Softer Is Better for Titanium: Molecular Titanium Arsenido Anions Featuring Ti≡As Bonding and a Terminal Parent Arsinidene.

We introduce the arsenido ligand onto the Ti ion, yielding a remarkably covalent Ti≡As bond and the parent arsinidene Ti═AsH moiety. An anionic arsenido ligand is assembled via reductive decarbonylation involving the discrete Ti salt [K(cryptand)][(PN)TiCl] () (cryptand = 222-Kryptofix) and Na(OCAs)(dioxane) in thf/toluene to produce the mixed alkali ate-complex [(PN)Ti(As)](μ-KNa(thf)) () and the discrete salt [K(cryptand)][(PN)Ti≡As] () featuring a terminal Ti≡As ligand. Protonation of or with various weak acids cleanly forms the parent arsinidene [(PN)Ti═AsH] (), which upon deprotonation with KCHPh in thf generates the more symmetric anionic arsenido [(PN)Ti(As){μ-K(thf)}] ().

Metallacyclobuta-(2,3)-diene: A Bidentate Ligand for Stream-line Synthesis of First Row Transition Metal Catalysts for Cyclic Polymerization of Phenylacetylene.

Described here is a direct entry to two examples of 3d transition metal catalysts that are active for the cyclic polymerization of phenylacetylene, namely, [(BDI)M{κ -C,C-(Me SiC SiMe )}] (2-M) (BDI=[ArNC(CH )] CH , Ar=2,6- Pr C H ; M=Ti, V). Catalysts are prepared in one step by the treatment of [(BDI)MCl ] (1-M, M=Ti, V) with 1,3-dilithioallene [Li (Me SiC SiMe )]. Complexes 2-M have been spectroscopically and structurally characterized and the polymers that are catalytically formed from phenylacetylene were verified to have a cyclic topology based on a combination of size-exclusion chromatography (SEC) and intrinsic viscosity studies.

Phosphorylated tau in Alzheimer's disease.

There is a need for blood biomarkers to detect individuals at different Alzheimer's disease (AD) stages because obtaining cerebrospinal fluid-based biomarkers is invasive and costly. Plasma phosphorylated tau proteins (p-tau) have shown potential as such biomarkers. This systematic review was conducted according to the PRISMA guidelines and aimed to determine whether quantification of plasma tau phosphorylated at threonine 181 (p-tau181), threonine 217 (p-tau217) and threonine 231 (p-tau231) is informative in the diagnosis of AD.

The Association of suPAR with Cardiovascular Risk Factors in Young and Healthy Adults.

The soluble urokinase plasminogen activator receptor (suPAR), as a correlate of chronic low-grade inflammation, may be used to predict individual cardiovascular risk. Since chronic low-grade inflammation is thought to be associated with the development of cardiovascular disease, this study aimed to evaluate if suPAR plasma levels are correlated with cardiovascular risk factors in young and healthy adults (aged 25-41 years). Consequently, data from the GAPP (genetic and phenotypic determinants of blood pressure and other cardiovascular risk factors) study were used to investigate suPAR plasma levels in relation to the following cardiovascular risk factors and laboratory parameters: BMI, physical activity, alcohol consumption, smoking status, blood pressure parameters, glucose status, and lipid levels.

Concentrations of Serum Brain Injury Biomarkers Following SARS-CoV-2 Infection in Individuals with and without Long-COVID-Results from the Prospective Population-Based COVI-GAPP Study.

It is unknown whether neurological symptoms are associated with brain injury after SARS-CoV-2 infections and whether brain injury and related symptoms also emerge in Long-COVID patients. Biomarkers such as serum neurofilament light chain (sNfL) and glial fibrillary acidic protein (sGFAP) can be used to elucidate neuro-axonal and astroglial injuries. We investigated whether these biomarkers are associated with COVID-19 infection status, associated symptoms and Long-COVID.

A mononuclear, terminal titanium(III) imido.

We report the first mononuclear Ti complex possessing a terminal imido ligand. Complex [TpTi{NSi(CH)}(THF)] (2) (Tp = hydridotris(3--butyl-5-methylpyrazol-1-yl)borate) is prepared by reduction of [TpTi{NSi(CH)}(Cl)] (1) with KC in high yield. The connectivity and metalloradical nature of 2 were confirmed by single crystal X-ray diffraction studies, Q- and X-band EPR, UV-Vis and H NMR spectroscopies.

Spectroscopic and Magnetic Studies of Co(II) Scorpionate Complexes: Is There a Halide Effect on Magnetic Anisotropy?

The observation of single-molecule magnetism in transition-metal complexes relies on the phenomenon of zero-field splitting (ZFS), which arises from the interplay of spin-orbit coupling (SOC) with ligand-field-induced symmetry lowering. Previous studies have demonstrated that the magnitude of ZFS in complexes with 3d metal ions is sometimes enhanced through coordination with heavy halide ligands (Br and I) that possess large free-atom SOC constants. In this study, we systematically probe this "heavy-atom effect" in high-spin cobalt(II)-halide complexes supported by substituted hydrotris(pyrazol-1-yl)borate ligands (Tp and Tp).

Linewidth, field, and frequency in electron paramagnetic resonance (EPR) spectroscopy.

EPR spectroscopy requires a combination of fixed microwave radiation and resonant external magnetic field. Bigger is not necessarily better in that low-frequency and -field EPR (LFEPR) can provide useful information as well as reduced linewidths that can allow better observation of hyperfine coupling. More importantly, LFEPR allows very low g values to be readily observed, such as often found in low-spin d systems.

Structural and Spectroscopic Characterization of a Zinc-Bound -Oxyphthalimide Radical.

Thermolysis of a 1:1:1 mixture of LH (L = {(2,6-PrCH)NC(Me)}CH), -hydroxyphthalimide (HOPth), and diethylzinc in toluene at 77 °C provided [LZn(OPth)] () in good yield after workup. The subsequent reduction of with 1.3 equiv of KC and 1 equiv of 2.

Photoelectrochemical Conversion of Dinitrogen to Benzonitrile: Selectivity Control by Electrophile- versus Proton-Coupled Electron Transfer.

Nitride complexes are key species in homogeneous nitrogen fixation to NH via stepwise proton-coupled electron transfer (PCET). In contrast, direct generation of nitrogenous organic products from N -derived nitrides requires new strategies to enable efficient reductive nitride transfer in the presence of organic electrophiles. We here present a 2-step protocol for the conversion of dinitrogen to benzonitrile.

Tale of Three Molecular Nitrides: Mononuclear Vanadium (V) and (IV) Nitrides As Well As a Mixed-Valence Trivanadium Nitride Having a VN Double-Diamond Core.

Transmetallation of [VCl(THF)] and [TlTp] afforded [(Tp)VCl] (, Tp = hydro-tris(3-butyl-5-methylpyrazol-1-yl)borate), which was reduced with KC to form a symmetric V complex, [(Tp)VCl] (). Complex has a high-spin ( = 1) ground state and displays rhombic high-frequency and -field electron paramagnetic resonance (HFEPR) spectra, while complex has an = 3/2 A ground state observable by conventional EPR spectroscopy. Complex reacts with NaN to form the V nitride-azide complex [(Tp)V≡N(N)] ().

Paramagnetic resonance investigation of mono- and di-manganese-containing systems in biochemistry.

Although not as important as iron, manganese is one of the key transition metal (d block) elements in biochemistry. The role of Mn in photosynthesis is perhaps its "starring role," but has been extensively covered elsewhere and will not be discussed in this chapter. In contrast to iron, for which Fe Mӧssbauer effect (nuclear gamma resonance) spectroscopy is available, Mn (100% abundant) lacks this ability.

P-tau217 in Alzheimer's disease.

Background And Aims: The potential of disease-modifying therapies for Alzheimer's disease has greatly stimulated interest in the development of minimally invasive testing for early identification of at-risk individuals. Accordingly, identification of blood-based biomarkers is paramount. The recent discovery of plasma phosphorylated at threonine217 (p-tau217) may provide a turning point in Alzheimer's disease detection.

Ruthenium-nitrosyl complexes as NO-releasing molecules, potential anticancer drugs, and photoswitches based on linkage isomerism.

The synthesis of new types of mono- and polynuclear ruthenium nitrosyl complexes is driving progress in the field of NO generation for a variety of applications. Light-induced Ru-NO bond dissociation in solution may involve transient linkage isomers MS1 (Ru-ON) and MS2 (Ru-η-NO), which can be detected spectroscopically and analyzed computationally. The investigation of photoisomerization processes in the solid state may be useful for potential application of such complexes for data storage, photochromic or photomagnetic materials or even non-linear optics.

Cooperative Activation of CO and Epoxide by a Heterobinuclear Al-Fe Complex via Radical Pair Mechanisms.

Activation of inert molecules like CO is often mediated by cooperative chemistry between two reactive sites within a catalytic assembly, the most common form of which is Lewis acid/base bifunctionality observed in both natural metalloenzymes and synthetic systems. Here, we disclose a heterobinuclear complex with an Al-Fe bond that instead activates CO and other substrates through cooperative behavior of two radical intermediates. The complex L(Me)AlFp (, L = HC{(CMe)(2,6-PrCHN)}, Fp = FeCp(CO), Cp = η-CH) was found to insert CO and cyclohexene oxide, producing LAl(Me)(μ:κ-OC)Fp () and LAl(Me)(μ-OCH)Fp (), respectively.

The Ruthenium Nitrosyl Moiety in Clusters: Trinuclear Linear μ-Hydroxido Magnesium(II)-Diruthenium(II), μ-Oxido Trinuclear Diiron(III)-Ruthenium(II), and Tetranuclear μ-Oxido Trigallium(III)-Ruthenium(II) Complexes.

The ruthenium nitrosyl moiety, {RuNO}, is important as a potential releasing agent of nitric oxide and is of inherent interest in coordination chemistry. Typically, {RuNO} is found in mononuclear complexes. Herein we describe the synthesis and characterization of several multimetal cluster complexes that contain this unit.

Hydrocarbon Oxidation by an Exposed, Multiply Bonded Iron(III) Oxo Complex.

The iron oxo unit, [Fe=O] is a critical intermediate in biological oxidation reactions. While its higher oxidation states are well studied, relatively little is known about the least-oxidized form [Fe=O]. Here, the thermally stable complex PhB(AdIm)Fe=O has been structurally, spectroscopically, and computationally characterized as a iron(III) oxo.

Electronic Structure and Magnetic Properties of a Low-Spin Cr Complex: -[CrCl(dmpe)] (dmpe = 1,2-Bis(dimethylphosphino)ethane).

Octahedral coordination complexes of the general formula -[MX(RECHCHER)] (M = Ti, V, Cr, Mn; E = N, P; R = alkyl, aryl) are a cornerstone of both coordination and organometallic chemistry, and many of these complexes are known to have unique electronic structures that have been incompletely examined. The -[CrCl(dmpe)] complex (dmpe = MePCHCHPMe), originally reported by Girolami and co-workers in 1985, is a rare example of a six-coordinate d system with an = 1 (spin triplet) ground state, as opposed to the high-spin ( = 2, spin quintet) state. The ground-state properties of = 1 systems are challenging to study using conventional spectroscopic methods, and consequently, the electronic structure of -[CrCl(dmpe)] has remained largely unexplored.