Mechanism of the Visible-Light-Promoted C(sp3)-H Oxidation via Uranyl Photocatalysis.

Uranyl cation, as an emerging photocatalyst, has been successfully applied to synthetic chemistry in recent years and displayed remarkable catalytic ability under visible light. However, the molecular-level reaction mechanisms of uranyl photocatalysis are unclear. Here, we explore the mechanism of the stepwise benzylic C-H oxygenation of typical alkyl-substituted aromatics (i.e., toluene, ethylbenzene, and cumene) via uranyl photocatalysis using theoretical and experimental methods. Theoretical calculation results show that the most favorable reaction path for uranyl photocatalytic oxidation is as follows: first, hydrogen atom transfer (HAT) from the benzyl position to form a carbon radical ([R•]), then oxygen addition ([R•] + O2 → [ROO•]), then radical-radical combination ([ROO•] + [R•] → [ROOR] → 2[RO•]), and eventually [RO•] reduction to produce alcohols, of which 2° alcohol would further be oxidized to ketones and 1° would be stepwise-oxygenated to acids. The results of the designed verification experiments and the capture of reactive intermediates were consistent with those of theoretical calculations and the previously reported research that the active benzylic C-H would be stepwise-oxygenated in the presence of uranyl. This work deepens our understanding of the HAT mechanism of uranyl photocatalysis and provides important theoretical support for the relevant application of uranyl photocatalysts in organic transformation.

Cyanide-Bridged Fe-Co Polynuclear Clusters Based on Four-Coordinate Cobalt(II).

Treatment of CoCl2·6H2O and tris(pyrazolyl-1-yl)borate tricyanoiron(III) anions at 55 °C afforded a series of new Fe-Co polynuclear clusters: {Co2Cl2(DMF)4[(Tp4-Me)Fe(CN)3]2} (1; Tp4-Me = hydridotris(4-methylpyrazol-1-yl)borate), (H3O+)@{Co4Cl4[(Tp4-Me)Fe(CN)3]4} (2), (MePh3P)4{Co6Cl6[(Tp4-Me)Fe(CN)3]6}·15CH3CN·3CH3OH·2H2O (3), and (BnEt3N)4{Co5Cl8[(Tp*)Fe(CN)3]4}·4CH3CN·2H2O (4; Tp*= hydridotris(3,5-dimethylpyrazol-1-yl)borate). They feature an asymmetric [Fe2Co2(CN)4] square, a pseudocubic [Fe4Co4(CN)12] cluster, a distorted-hexagonal-prism-shaped [Fe6Co6(CN)18] cage, and a bis(trigonal-bipyramidal) cluster of [Fe4Co5(CN)12] fused at one cobalt center, respectively. The Co(II) ions adopt a four-coordinate tetrahedral geometry except for half of 1 in an octahedral geometry. It should be mentioned that 3 and 4 provide two novel molecular skeletons in the cyanometalate family. Interestingly, 1 behaved as a single-molecule magnet with an effective energy barrier for spin reverse of 30.7 K at zero dc field. Our result demonstrated a possible self-assembly route toward high-nuclearity cyanide-bridged clusters by introducing four-coordinate cobalt(II) ions.

Thyroid function of twin-pregnant women in early pregnancy.

BACKGROUND: Serum human chorionic gonadotrophin (hCG) is higher in twin than that in singleton pregnancies. As hCG stimulates the thyroid to produce more free thyroxine (FT4), which may lead to decreased thyroid-stimulating hormone (TSH) levels, the reference ranges of thyroid-related indicators may differ between singleton and twin pregnancies in the first trimester. This study aimed to establish reference ranges for thyroid-related indicators in early twin pregnancies and to compare them with singleton pregnancies. METHODS: Data of 820 twin-pregnant women were extracted from the established database of all pregnant women who delivered at Peking University First Hospital from October 2013 to May 2018; 160 who met National Academy of Clinical Biochemistry criteria were included to establish TSH and FT4 reference ranges. We screened 480 (3:1 paired) women with singleton pregnancies from the same database as controls. The Mann-Whitney test for TSH and FT4 levels was applied for comparisons between singleton and twin pregnancies. RESULTS: First-trimester reference ranges (4-12 gestational weeks) for twin pregnancies were: TSH 0.69 (0.01-3.35) mIU/L and FT4 16.38 (12.45-23.34) pmol/L. Median TSH was significantly lower at 7 to 12 gestational weeks than that at 4 to 6 gestational weeks (0.62 vs. 0.96 mIU/L, Z = -1.964, P = 0.049); FT4 was not significantly different between the two groups. Compared to singleton pregnancies, median TSH was significantly lower (0.69 vs. 1.27 mIU/L, Z = -6.538, P = 0.000), and FT4 was significantly higher (16.38 vs. 14.85 pmol/L, Z = -7.399, P = 0.000) in twin pregnancies in the first trimester. CONCLUSIONS: Specific reference ranges for thyroid-related indicators for twin pregnancies are needed to avoid a misdiagnosis of thyroid dysfunction. Moreover, establishment of separate reference ranges for 4 to 6 and 7 to 12 gestational weeks in twin pregnancies may be considered.