A Low‐Spin Three‐Coordinate Cobalt(I) Complex and Its Reactivity toward H2 and Silane

A three‐coordinate low‐spin cobalt(I) complex generated using a pincer ligand is presented. Since an empty orbital is sterically exposed at the site trans to the N donor of an acridane moiety, the cobalt(I) center accepts the coordination of various donors such as H₂ and PhSiH₃ revealing σ‐complex formation. At this low‐spin cobalt(I) site, homolysis of H–H and Si?H bonds preferentially occurs via bimolecular hydrogen atom transfer instead of two‐electron oxidative addition. When the resulting Co^II–H species was exposed to N₂, H₂ evolution readily occurs at ambient conditions. These results suggest single‐electron processes are favored at the structurally rigidified cobalt center.     

Modeling dioxygen-activating centers in non-heme diiron enzymes: carboxylate shifts in diiron(II) complexes supported by sterically hindered carboxylate ligands

General synthetic routes are described for a series of diiron(II) complexes supported by sterically demanding carboxylate ligands 2,6-di(p-tolyl)benzoate (Ar(Tol)CO(2)(-)) and 2,6-di(4-fluorophenyl)benzoate (Ar(4-FPh)CO(2)(-)). The interlocking nature of the m-terphenyl units in self-assembled [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (L = C(5)H(5)N (4); 1-MeIm (5)) promotes the formation of coordination geometries analogous to those of the non-heme diiron cores in the enzymes RNR-R2 and Delta 9D. Magnetic susceptibility and M?ssbauer studies of 4 and 5 revealed properties consistent with weak antiferromagnetic coupling between the high-spin iron(II) centers. Structural studies of several derivatives obtained by ligand substitution reactions demonstrated that the [Fe(2)(O(2)CAr')(4)L(2)] (Ar' = Ar(Tol); Ar(4-FPh)) module is geometrically flexible. Details of ligand migration within the tetracarboxylate diiron core, facilitated by carboxylate shifts, were probed by solution variable-temperature (19)F NMR spectroscopic studies of [Fe(2)(mu-O(2)CAr(4-FPh))(2)-(O(2)CAr(4-FPh))(2)(THF)(2)] (8) and [Fe(2)(mu-O(2)CAr(4-FPh))(4)(4-(t)BuC(5)H(4)N)(2)] (12). Dynamic motion in the primary coordination sphere controls the positioning of open sites and regulates the access of exogenous ligands, processes that also occur in non-heme diiron enzymes during catalysis.     

Elimination of amino acid interferences in the chiral ligand-exchange chromatographic analysis of lactic acid enantiomers in wine

Chiral ligand-exchange liquid chromatography is used to identify and quantitate lactic acid enantiomers in wines that have or have not undergone malolactic fermentation. The stationary phase is (R)-penicillamine, which is bound lipophilically to a C18 bonded silica matrix. The mobile phase is 1mM copper sulfate, and the detection mode is ultraviolet. Serious interference from (S)-aspartic acid and other amino acids is eliminated by the use of propanesulfonic acid-type cation exchange solid-phase extraction cartridges prior to chromatographic analysis. Lactic acid enantiomers in wine are quantitated in the range of 10 to 500 mg/L. The detection limit is 3 mg/L. The method is also successful in the determination of lactic acid enantiomers in certain beers (e.g., lambic beers), kim-chi, sauerkraut, and various yogurts.     

A series of long-chain lamellar hydrated copper(II) alkylsulfonates with different chain molecular assemblies

Reaction of copper(II) salts with n-alkylsulfonate anions yields light blue lamellar Cu(C(n)H(2n + 1)SO3)2 x zH2O displaying distinct (mono/bi-layer) chain packing with increasing alkyl chain lengths. This may be attributed to the amphiphilic nature of the surfactants, i.e., the hydrophilic sulfonate head groups, mediating the coordination, and H-bonding interactions, and the hydrophobic alkyl chains.     

Skin Necrosis due to Photodynamic Action of Benzoporphyrin Depends on Circulating Rather than Tissue Drug Levels: Implications for Control of Photodynamic Therapy

In an ideal world, photodynamic therapy (PDT) of abnormal tissue would reliably spare the surrounding normal tissue. Normal tissue responses set the limits for light and drug dosimetry. The threshold fluence for necrosis (TFN) was measured in normal skin following intravenous infusion with a photosensitizer, benzoporphyrin derivative monoacid ring A (BPD-MA) Verteporfin as a function of drug dose (0.25-2.0 mg/kg), wavelength of irradiation (458 and 690 nm) and time interval (0–5h) between drug administration and irradiation. The BPD-MA levels were measured in plasma and skin tissue to elucidate the relationship between TFN, drug kinetics and biodistribution. The PDT response of normal skin was highly reproducible. The TFN for 458 and 690 nm wavelengths was nearly identical and the estimated quantum efficiency for skin response was equal at these two wavelengths. Skin phototoxicity, quantified in terms of 1/ TFN, closely correlated with the plasma pharmacokinetics rather than the tissue pharmacokinetics and was quadratically dependent on the plasma drug concentration regardless of the administered drug dose or time interval between drug and light exposure. This study strongly suggests that noninvasive measurements of the circulating drug level at the time of light treatment will be important for setting optimal light dosimetry for PDT with liposomal BPD-MA, a vascular photosensitizer.     

Chronic Low-Dose UVA Irradiation Induces Local Suppression of Contact Hypersensitivity, Langerhans Cell Depletion and Suppressor Cell Activation in C3H/HeJ Mice

Abstract— It has previously been demonstrated that chronic low-dose solar-simulated UV radiation could induce both local and systemic immunosuppression as well as tolerance to a topically applied hapten. In this study, we have used a chronic low-dose UV-irradiation protocol to investigate the effects of UVA on the skin immune system of C3H/HeJ mice. Irradiation with UVA+B significantly suppressed the local and systemic primary contact hypersensitivity (CHS) response to the hapten 2,4,6-trinitrochlo-robenzene. Furthermore UVA+B reduced Langerhans cell (LC) and dendritic epidermal T cell (DETC) densities in chronically UV-irradiated mice. Ultraviolet A irradiation induced local, but not systemic, immunosuppression and reduced LC (32%) but not DETC from the epidermis compared to the shaved control animals. Treatment of mice with both UVA+B and UVA radiation also induced an impaired secondary CHS response, and this tolerance was transferable with spleen cells. These results suggest that depletion of LC, but not DETC, may be involved in UVA-induced local immunosuppression in our model, and that tolerance was induced in the presence of normal numbers of DETC. Hence exposure of C3H/HeJ mice 5 days per week for 4 weeks with UVA can induce local immunosuppression and tolerance.     

Semiempirical mo studies on the proton transfer equilibria of amides

Intramolecular proton transfer equilibria of acetamide and methyl carbamate have been studied by AMI MO calculations, and the results are compared with those of the MNDO method. It was found that the two semi- empirical methods predict essentially the same proton transfer mechanism, but MNDO tends to overestimate the activation barriers. Participation of one solvate vater in the proton transfer led to a considerable lovering of the activation barrier, by nearly the same amount, in both methods. One notable conflict between the two methods was that the methoxy-O-protonated form of methyl carbamate, in the gas phase, can be a local energy minimum with MNDO, whereas it leads to dissociation into two species Instead of an optimized structure with AM1. It was concluded that the MNDO method can be useful for this type of process, especially when one is interested in the relative activation barriers only.     

Synthesis of some heterocyclic skeletons via organoiron complexes. Crystal and molecular structure of (5a,6,7,8,9,9a-η6-1,4-benzoxathiino[3,2-b]pyridine)(η5-cyclopentadienyl)iron hexafluorophosphate

Synthesis of the heterocyclic skeletons of some biologically active compounds from (η⁶-o-dichlorobenzene)(η⁵-cyclopentadienyrl)iron hexafluorophosphate in a two step procedure is described. Cyclopentadienyliron hexafluorophosphate complexes of 1,4-benzodioxino[2,3-b]pyridine, 1,4-benzoxathiino[3,2-b]pyridine, 10H-pyrido[3,2-b]benzoxazine, benzo[b]naphtho[2,3-e][1,4]dioxin, 4-methylbenzo[b]benzopyran-2-one[7,6-e][1,4]dioxin and benzo[b]anthracen-9,10-diono[1,2-e][1,4]dioxin were isolated and characterized. Upon pyrolytic sublimation of these complexes the free heterocycles were obtained and characterized. (η⁶-1,4-Benzoxathiino[3,2-b]pyridine)(η⁵-cyclopentadienyl)iron hexafluorophosphate crystalizes in the orthothombic system, space group Pbca; the dihedral angle between the planes of outer rings was found to be 176.8 (1).     

Mass spectra of complexes of 8-quinolinol with trivalent metals (AL,Ga, In,Sc, Cr and Fe)

The main fragmentation of the compounds MX_3-nox_n (oxH=8-quinolinol. n = 3; M=AL, Ga, In, Sc, Cr or Fe. n = 2; M=In or Fe; X=Cl or Br. InIox₂. n = 1; M=AL, In or Fe; X= Cl or Br) involves loss of X and intact ox_. radicals. The comparative abundances of the fragments are primarily related to the common oxidation states of the metals. For example, all the Mox₃ compounds show the ions [Mox₃]⁺ and [Mox₂]⁺. The ions [Mox]⁺ and [M]⁺ are present when M=Ga, In, Cr or Fe but for the elements with only one oxidation state (Al or Sc) [M]⁺ is absent and [Mox]⁺ has only very low abundance. When M= Cr or Fe metal-containing ions arising from loss of species such as CO, H₂O, HX, C₂H₂, H and OH by fragmentation of the ox ligand are also present; this behaviour is rationalised in terms of the ability of these metals to undergo a unit change in oxidation state. When n=1 the ions [MXox₂]⁺ and [Mox₂]⁺ and when n= 2 the ions [MX₂ox]⁺ and [Mox₃]⁺ are present; these ions arise by ionization and fragmentation of species formed by redistribution reactions in the mass spectrometer.