Oxygen activation in all heme enzymes requires the formation of high oxidation states of iron, usually referred to as ferryl heme. There are two known intermediates: Compound I and Compound II. The ...nature of the ferryl heme—and whether it is an FeIV=O or FeIV‐OH species—is important for controlling reactivity across groups of heme enzymes. The most recent evidence for Compound I indicates that the ferryl heme is an unprotonated FeIV=O species. For Compound II, the nature of the ferryl heme is not unambiguously established. Here, we report 1.06 Å and 1.50 Å crystal structures for Compound II intermediates in cytochrome c peroxidase (CcP) and ascorbate peroxidase (APX), collected using the X‐ray free electron laser at SACLA. The structures reveal differences between the two peroxidases. The iron‐oxygen bond length in CcP (1.76 Å) is notably shorter than in APX (1.87 Å). The results indicate that the ferryl species is finely tuned across Compound I and Compound II species in closely related peroxidase enzymes. We propose that this fine‐tuning is linked to the functional need for proton delivery to the heme.
Enzymatic fine‐tuning of heme reactivity: Free‐electron laser crystal structures of two different heme‐containing peroxidases—cytochrome c peroxidase and ascorbate peroxidase—show differences in the nature of the ferryl species. Precise enzymatic fine‐tuning within structurally similar heme active sites is implicated.
The first isolated examples of intermolecular oxidative addition of alkenyl and alkynyl iodides to AuI are reported. Using a 5,5′‐difluoro‐2,2′‐bipyridyl ligated complex, oxidative addition of ...geometrically defined alkenyl iodides occurs readily, reversibly and stereospecifically to give alkenyl‐AuIII complexes. Conversely, reversible alkynyl iodide oxidative addition generates bimetallic complexes containing both AuIII and AuI centers. Stoichiometric studies show that both new initiation modes can form the basis for the development of C−C bond forming cross‐couplings.
The first isolated examples of intermolecular oxidative addition of alkenyl and alkynyl iodides to AuI are reported. Stoichiometric studies show that both new initiation modes can form the basis for the development of C−C bond forming cross‐couplings.
Syntheses and characterisation of group ten complexes containing the ligand diphenyl‐2‐(3‐methyl)indolylphosphine are presented herein. The complexes trans‐PdCl2{PPh2(C9H8N)}2 (1), ...cis‐PtCl2{PPh2(C9H8N)}2 (2), trans‐Pd(CH3)Cl{PPh2(C9H8N)}2 (3) and trans‐Pt(CH3)Cl{PPh2(C9H8N)}2 (4) have all been structurally characterized by X‐ray crystallography. In all cases, the ligands coordinate to the metal centres via the phosphorus donor atom (κ1‐P) and the pendent NH groups on the indolyl rings of the ligand are orientated so that there is some degree of interaction with the metal–chloride bonds. The unexpected reactivity of 4 with NaB{3,5‐C6H3(CF3)2}4 is also reported. In this case, the product resulting from this reaction was found to be Pt{3,5‐C6H3(CF3)2}2{PPh2(C9H8N)}2.
Palladium and platinum complexes containing diphenyl‐2‐(3‐methyl)indolylphosphine were prepared and characterised. Their crystal structures revealed interactions of the indolyl units with the metal–chloride bonds directed at various positions along this bond. The complex PtMeCl(L2) was shown to cleave B–C bonds in the B{3,5‐C6H3(CF3)2}4 anion.
Organelle movement in plants cells is extremely dynamic. Movement is driven by the acto-myosin system. Higher plant myosins fall into two classes: classes XI and VIII. Localization studies have ...highlighted that myosins are present throughout the cytosol, label motile puncta and decorate the nuclear envelope and plasma membrane. Functional studies through expression of dominant-negative myosin variants, RNAi (RNA interference) and T-DNA insertional analysis have shown that class XI myosins are required for organelle movement. Intriguingly, organelle movement is also linked to Arabidopsis growth and development. The present review tackles current findings relating to plant organelle movement and the role of myosins.
A series of novel, intramolecular Zr(IV)/P frustrated Lewis pairs (FLPs) based on cationic zirconocene fragments with a variety of ancillary cyclopentadienyl and 2-phosphinoaryloxide (−O(C6H4)PR2, ...R = tBu and 3,5-CF3-(C6H3)) ligands are reported and their activity as catalysts for the dehydrocoupling of dimethylamine–borane (Me2NH·BH3) assessed. The FLP system (C9H7)2ZrO(C6H4)PtBu2B(C6F5)4 is shown to give unprecedented turnover frequencies (TOF) for a catalyst based on a group 4 metal (TOF ≥ 600 h–1), while also proving to be the most efficient FLP catalyst reported to date. The mechanism of this reaction has been probed using analogous intermolecular Zr(IV)/P FLPs, permitting deconvolution of the reactions taking place at both the Lewis acidic and basic sites. Elucidation of this mechanism revealed an interesting cooperative two-cycle process where one cycle is FLP mediated and the other, a redistribution of a linear diborazane intermediate, relies solely on the presence of a Zr(IV) Lewis acid.
Objectives
To detect the incidence of clinically important thoracic and abdominal imaging abnormalities in patients with neurological signs but with no clinical signs or laboratory findings ...consistent with thoracic or abdominal disease.
Materials and Methods
Review of imaging findings in dogs with neurological signs but no thoracic or abdominal signs that underwent thoracic, or thoracic and abdominal screening during the same hospitalisation as the neurological investigation.
Results
Two hundred and six dogs were included in the thoracic study. Of those, only eight (3.9%) had clinically important findings and in only five cases (2.4%) were the findings related to pathology identified on MRI. One hundred and forty‐seven dogs were included in the abdominal study. Abnormalities were found in 23 dogs (15.6%), but in only eight (5.4%) were they considered to be of current clinical importance and in only three (2%) were they related to the pathology identified on MRI. Ultrasonography provided valuable additional information in 22 cases (15%) but this was only considered important in four (2.7%) and related to the neurological condition in one (0.7%). As expected, abdominal ultrasonography often provided more information than radiography alone in the abdominal screening but this was rarely clinically relevant or related to the reason for referral.
Clinical Significance
Thoracic and abdominal screening of neurological patients with no clinically evident thoracic or abdominal clinical signs only infrequently identified occult but clinically important pathology which changed the current management plan, regardless of neurolocalisation or age.
Palladium(II) acetate is readily converted into Pd3(μ2‐OH)(OAc)5 (1) in the presence of water in a range of organic solvents and is also slowly converted in the solid state. Complex 1 can also be ...formed in nominally anhydrous solvents. Similarly, the analogous alkoxide complexes Pd3(μ2‐OR)(OAc)5 (3) are easily formed in solutions of palladium(II) acetate containing a range of alcohols. An examination of a representative Wacker‐type oxidation shows that the Pd‐OH complex 1 and a related Pd‐oxo complex 4 can be excluded as potential catalytic intermediates in the absence of exogenous water.
When is palladium acetate not palladium acetate? Anywhere near trace amounts of water or alcohols. Palladium acetate is extremely sensitive to hydrolysis in solution and moderately so in the solid state. The resulting hydroxide complex is likely to be the true starting point for many reactions and catalytic processes that are reported as using palladium acetate.
Expression and tracking of fluorescent fusion proteins has revolutionized our understanding of basic concepts in cell biology. The protocol presented here has underpinned much of the in vivo results ...highlighting the dynamic nature of the plant secretory pathway. Transient transformation of tobacco leaf epidermal cells is a relatively fast technique to assess expression of genes of interest. These cells can be used to generate stable plant lines using a more time-consuming, cell culture technique. Transient expression takes from 2 to 4 days whereas stable lines are generated after approximately 2 to 4 months.
Halide abstraction from the ruthenium N-heterocyclic carbene complex Ru(IPr)2(CO)HCl (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with NaBAr4 F (BAr4 F = B{C6H3(3,5-CF3)2}4) gave the ...salt Ru(IPr)2(CO)HBAr4 F (2), which was shown through a combined X-ray/neutron structure refinement and quantum theory of atoms in molecules (QTAIM) study to contain a bifurcated Ru···η3-H2C ξ-agostic interaction involving one iPr substituent of the IPr ligand. This system complements the previously reported Ru(IMes)2(CO)H+ cation (IMes =1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), where a non-agostic form is favored. Treatment of 2 with CO, H2, and the amine–boranes H3B·NR2H (R = Me, H) gave Ru(IPr)2(CO)3HBAr4 F (3), Ru(IPr)2(CO)(η2-H2)HBAr4 F (4), and Ru(IPr)2(CO)(κ2-H2BH·NR2H)HBAr4 F (R = Me, 5; R = H, 6), respectively. Heating 5 in the presence of Me3SiCHCH2 led to alkene hydroboration and formation of the C–H activated product Ru(IPr)(IPr)′(CO)BAr4 F (7). X-ray characterization of 3 and 5–7 was complemented by DFT calculations, and the mechanism of H2/H exchange in 4 was also elucidated. Treatment of 2 with HBcat resulted in Ru–H abstraction to form the boryl complex Ru(IPr)2(CO)(Bcat) BAr4 F (8), which proved to be competent in the catalytic hydroboration of 1-hexene. In 8, a combined X-ray/neutron structure refinement and QTAIM analysis suggested the presence of a single Ru···η2-HC ξ-agostic interaction.
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