Electron-Rich Metal Cations Enable Synthesis of High Molecular Weight, Linear Functional Polyethylenes.

Group 10 metal catalysts have shown much promise for the copolymerization of nonpolar with polar alkenes to directly generate functional materials, but access to high copolymer molecular weights nevertheless remains a key challenge toward practical applications in this field. In the context of identifying new strategies for molecular weight control, we report a series of highly polarized P(V)-P(III) chelating ligands that manifest unique space filling and electrostatic effects within the coordination sphere of single component Pd polymerization catalysts and exert important influences on (co)polymer molecular weights. Single component, cationic phosphonic diamide-phosphine (PDAP) Pd catalysts are competent to generate linear, functional polyethylenes with Mw up to ca. 2 × 105 g mol-1, significantly higher than prototypical catalysts in this field, and with polar content up to ca. 9 mol %. Functional groups are positioned by these catalysts almost exclusively along the main chain, not at chain ends or ends of branches, which mimics the microstructures of commercial linear low-density polyethylenes. Spectroscopic, X-ray crystallographic, and computational data indicate PDAP coordination to Pd manifests cationic yet electron-rich active species, which may correlate to their complementary catalytic properties versus privileged catalysts such as electrophilic α-diimine (Brookhart-type) or neutral phosphine-sulfonato (Drent-type) complexes. Though steric blocking within the catalyst coordination sphere has long been a reliable strategy for catalyst molecular weight control, data from this study suggest electronic control should be considered as a complementary concept less prone to suppression of comonomer enchainment that can occur with highly sterically congested catalysts.

Density functional theory study of oxygen-atom insertion into metal-methyl bonds of iron(II), ruthenium(II), and osmium(II) complexes: study of metal-mediated C-O bond formation.

Metal-mediated C-O bond formation is a key step in hydrocarbon oxygenation catalytic cycles; however, few examples of this reaction have been reported for low-oxidation-state complexes. Oxygen insertion into a metal-carbon bond of Cp*M(CO)(OPy)R (Cp* = η(5)-pentamethylcyclopentadienyl; R = Me, Ph; OPy = pyridine-N-oxide; M = Fe, Ru, Os) was analyzed via density functional theory calculations. Oxygen-atom insertions through a concerted single-step organometallic Baeyer-Villiger pathway and a two-step pathway via a metal-oxo intermediate were studied; calculations predict that the former pathway was lower in energy. The results indicated that functionalization of M-R to M-OR (R = Me, Ph) is plausible using iron(II) complexes. Starting from Cp*Fe(CO)(OPy)Ph, the intermediate Fe-oxo showed oxyl character and, thus, is best considered an Fe(III)O(•-) complex. Oxidation of the π-acid ancillary ligand CO was facile. Substitutions of CO with dimethylamide and NH3 were calculated to lower the activation barrier by ∼1-2 kcal/mol for formation of the Fe(III)O(•-) intermediate, whereas a chloride ligand raised the activation barrier to 26 kcal/mol from 22.9 kcal/mol.

Variable pathways for oxygen atom insertion into metal-carbon bonds: the case of Cp*W(O)2(CH2SiMe3).

Cp*W(O)(2)(CH(2)SiMe(3)) (1) (Cp* = η(5)-pentamethylcyclopentadienyl) reacts with oxygen atom donors (e.g., H(2)O(2), PhIO, IO(4)(-)) in THF/water to produce TMSCH(2)OH (TMS = trimethylsilyl). For the reaction of 1 with IO(4)(-), the proposed pathway for alcohol formation involves coordination of IO(4)(-) to 1 followed by concerted migration of the -CH(2)TMS ligand to the coordinated oxygen of IO(4)(-) with concomitant dissociation of IO(3)(-) to produce Cp*W(O)(2)(OCH(2)SiMe(3)) (3), which undergoes protonolysis to yield free alcohol. In contrast to the reaction with IO(4)(-), the reaction of 1 with H(2)O(2) results in the formation of the η(2)-peroxo complex Cp*W(O)(η(2)-O(2))(CH(2)SiMe(3)) (2). In the presence of acid (HCl) or base (NaOH), complex 2 produces TMSCH(2)OH. The conversion of 2 to TMSCH(2)OH catalyzed by Brønsted acid is proposed to occur through protonation of the η(2)-peroxo ligand, which facilitates the transfer of the -CH(2)TMS ligand to a coordinated oxygen of the η(2)-hydroperoxo ligand. In contrast, the hydroxide promoted conversion of 2 to TMSCH(2)OH is proposed to involve hydroxide coordination, followed by proton transfer from the hydroxide ligand to the peroxide ligand to yield a κ(1)-hydroperoxide intermediate. The migration of the -CH(2)TMS ligand to the coordinated oxygen of the κ(1)-hydroperoxo produces an alkoxide complex, which undergoes protonolysis to yield free alcohol.

[Isolation of high osmotic-tolerant mutants of Escherichia coli for succinic acid production by metabolic evolution].

Succinic acid production was inhibited by high osmotic pressure caused by the accumulation of sodium ions in the process of two-stage fermentation by Escherichia coli using Na2CO3 as the pH regulator. To enhance the resistance of this strain to osmotic stress, the possibility to isolate high NaCl-tolerant mutant strain of Escherichia coli for succinic acid production by metabolic evolution was investigated. The metabolic evolution system was used as a mutant-generating system, allowing the cells to be continuously cultured at the maximum specific growth rate. The mutant strain can grow at maximum rate in the condition of high osmotic by gradually improving the concentration of NaCl in a continuous culture. Then the high osmotic-tolerant mutant strain of E. coli XB4 was selected with NaCl as the osmo-regulator. When using Na2CO3 as the pH regulator, E. coli XB4 was used in a 7.0 L fermenter during two-stage fermentation. After 60 h anaerobic fermentation, the mutant strain XB4 produced 69.5 g/L succinic acid with a productivity of 1.18 g/(L x h), which were increased by 18.6% and 20% compared with that of the parent strain.

Effects of four regulating-intestine prescriptions on pathology and ultrastructure of colon tissue in rats with ulcerative colitis.

AIM: To observe different histomorphologic changes of ulcerative colitis (UC) rats that were treated with four regulating-intestine prescriptions (FRIP), to investigate the curative effects of FRIP and to analyze their treatment mechanism. METHODS: The UC rat model was made by the method of 2,4-dinitro chloro benzene (DNCB) immunity and acetic acid local enema. Ninety-eight SD rats were randomly divided into seven groups, namely, the normal control group, model group, salicylazosulfapyridine (SASP) group, Wumeiwan (WMW) group, Baitouwengtang (BTWT) group, Senglingbaishusan (SLBSS) group, and Tongxieyaofang (TXYF) group. Each group had 14 rats (with equal ratio of male and female). The six animal model groups of UC -SASP, TXYF, WMW, BTWT, SLBSS, TXYF-were treated by distilled water except the normal control group. Changes of the rat's general conditions after treatment were respectively observed, the colon tissue damage scores were given out, the pathology of colonic mucosa and changes of ultrastructure were analyzed. RESULTS: Different pathological changes on histology were shown after treatment by FRIP. The colon tissue damage score in model group was higher than that of FRIP groups and SASP group (q = 4.59, 4.77, P<0.05 or q = 5.48, 6.25, 5.97, P<0.01). The scores of WMW group, BTWT group and SLBSS group were lower than that of SASP (q = 4.13, P<0.05 or q = 5.31, 5.12, P<0.01). There was no remarkable difference between the damage score of TXYF group and SASP group (q = 3.75, P>0.05). In addition, some apoptosis cells were found in the pathologic control group. CONCLUSION: The model made with DNCB and acetic acid was successful, and FRIP had better curative effect and WMW was the best curative effect, BTW, SLBSS and TXYF were similar to SASP, and we discovered that apoptosis was possibly related to UC.

Effects of Zuogui Wan on neurocyte apoptosis and down-regulation of TGF-beta1 expression in nuclei of arcuate hypothalamus of monosodium glutamate -liver regeneration rats.

AIM: To inquire into the effects and mechanism of Zuogui Wan (Pills for Kidney Yin) on neurocyte apoptosis in nuclei of arcuate hypothalamus (ARN) of monosodium glutamate (MSG)-liver regeneration rats, and the mechanism of liver regeneration by using optic microscope, electron microscope and in situ end labeling technology to adjust nerve-endocrine-immunity network. METHODS: Neurocyte apoptosis in ARN of the experiment rats was observed by using optic microscope, electron microscope and in situ end labeling technology. Expression of TGF-beta1 in ARN was observed by using immunohistochemistry method. RESULTS: The expression of TGF-beta1 in rats of model group was increased with the increase of ARN neurocyte apoptosis index (AI) (t = 8.3097, 12.9884, P<0.01). As compared with the rats of model group, the expression of TGF-beta1 in rats of Zuogui Wan treatment group was decreased with the significant decrease of ARN neurocyte apoptosis (t = 4.5624, 11.1420, P<0.01). CONCLUSION: Brain neurocyte calcium ion overexertion and TGF-beta1 protein participate in the adjustment and control of ARN neurocyte apoptosis in MSG-liver regeneration-rats. Zuogui Wan can prevent ARN neurocyte apoptosis of MSG-liver regeneration in rats by down-regulating the expression of TGF-beta1, and influence liver regeneration through adjusting nerve-endocrine-immune network.