Silver Surface-Assisted Dehydrobrominative Cross-Coupling between Identical Aryl Bromides.

Cross-coupling reactions represent an indispensable tool in chemical synthesis. An intriguing challenge in this field is to achieve selective cross-coupling between two precursors with similar reactivity or, to the limit, the identical molecules. Here we report an unexpected dehydrobrominative cross-coupling between 1,3,5-tris(2-bromophenyl)benzene molecules on silver surfaces. Using scanning tunneling microscopy, we examine the reaction process at the single-molecular level, quantify the selectivity of the dehydrobrominative cross-coupling, and reveal the modulation of selectivity by substrate lattice-related catalytic activity or molecular assembly effect. Theoretical calculations indicate that the dehydrobrominative cross-coupling proceeds via regioselective C-H bond activation of debrominated TBPB and subsequent highly selective C-C coupling of the radical-based intermediates. The reaction kinetics plays an important role in the selectivity for the cross-coupling. This work not only expands the toolbox for chemical synthesis but also provides important mechanistic insights into the selectivity of coupling reactions on the surface.

Unraveling the Dynamic Processes of Methanol Electrooxidation at Isolated Rhodium Sites by In Situ Electrochemical Scanning Tunneling Microscopy.

Materials with isolated single-atom Rh-N4 sites are emerging as promising and compelling catalysts for methanol electrooxidation. Herein, we carried out an in situ electrochemical scanning tunneling microscopy (ECSTM) investigation of the dynamic processes of methanol absorption and catalytic conversion in the rhodium octaethylporphyrin (RhOEP)-catalyzed methanol oxidation reaction at the molecular scale. The high-contrast RhOEP-CH3OH complex formed by methanol adsorption was visualized distinctly in the STM images. The Rh-C adsorption configuration of methanol on isolated rhodium sites was identified on the basis of a series of control experiments and theoretical simulation. The adsorption energy of methanol on RhOEP was obtained from quantitative analysis. In situ ECSTM experiments present an explicit description of the transformation of the intermediate species in the catalytic process. By qualitatively evaluating the rate constants of different stages in the reaction at the microscopic level, we considered the CO transformation/desorption as the critical step for determining the reaction dynamics. Methanol adsorption was found to be correlated with RhOEP oxidation in the initial stage of the reaction, and the dynamic information was revealed unambiguously by in situ potential step experiments. This work provides microscopic results for the catalytic mechanism of Rh-N4 sites for methanol electrooxidation, which is instructive for the rational design of the high-performance catalyst.

Probing the Synergistic Effects of Mg2+ on CO2 Reduction Reaction on CoPc by In Situ Electrochemical Scanning Tunneling Microscopy.

We report herein the in situ electrochemical scanning tunneling microscopy (ECSTM) study on the synergistic effect of Mg2+ in CO2 reduction reaction (CO2RR) catalyzed by cobalt phthalocyanine (CoPc). ECSTM measurement molecularly resolves the self-assembled CoPc monolayer on the Au(111) substrate. In the CO2 environment, high-contrast species are observed in the adlayer and assigned to the CO2 adsorption on CoPc. Furthermore, the contrast of the CO2-bound complex is higher in Mg2+-containing electrolytes than in Mg2+-free electrolytes, indicating the formation of the CoPc-CO2-Mg2+ complex. The surface coverage of adsorbed CO2 is positively correlated with the Mg2+ concentration as the additive in electrolytes up to a plateau of 30.8 ± 2.7% when c(Mg2+) > 30 mM. The potential step experiment indicates the higher CO2 adsorption dynamics in Mg2+-containing electrolytes than without Mg2+. The rate constants of CO2 adsorption and dissociation in different electrolytes are extracted from the data fitting of statistical results from in situ ECSTM experiments.

Evolution of Br⋯Br contacts in enantioselective molecular recognition during chiral 2D crystallization.

Halogen-mediated interactions play an important role in molecular recognition and crystallization in many chemical and biological systems, whereas their effect on homochiral versus heterochiral recognition and crystallization has rarely been explored. Here we demonstrate the evolution of Br⋯Br contacts in chiral recognition during 2D crystallization. On Ag(100), type I contacts prevail at low coverage and lead to homochiral recognition and the formation of 2D conglomerates; whereas type II contacts mediating heterochiral recognition are suppressed at medium coverage and appear in the racemates induced by structural transitions at high coverage. On Ag(111), type I contacts dominate the 2D crystallization and generate 2D conglomerates exclusively. DFT calculations suggest that the energy difference between type I and type II contacts is reversed upon adsorption due to the substrate induced mismatch energy penalty. This result provides fundamental understanding of halogen-mediated interactions in molecular recognition and crystallization on surface.

Aromatic Ring Fusion to Benzoporphyrin via γ-ortho Cyclodehydrogenation on a Ag(111) Surface.

Aromatic ring fusion to porphyrins and their derivatives represents an attractive route to tune the molecular conjugation and thus expand their functionalities. Here, we report the expansion of the aromatic π-system of palladium tetraphenyltetrabenzoporphyrins (Pd-TPTBP) via surface-assisted γ-ortho cyclodehydrogenation on Ag(111). The chemical transformation of Pd-TPTBP into different products at an elevated temperature of 600 K was revealed at the single-molecule level using bond-resolved scanning tunneling microscopy with a CO-functionalized tip. We captured a series of γ-ortho cyclodehydrogenation products, wherein the maximum extent to which the reaction can progress is associated with 7-fold C-C formation to afford nearly planar γ-ortho fused porphyrins with 66 conjugated π-electrons. In addition, a small number of molecules undergo C-C bond dissociation of meso-phenyl at elevated temperature, producing fully planar γ-ortho fused products lacking one or two phenyl moieties. Scanning tunneling spectroscopy measurements and DFT calculations suggest the electronic gap of the γ-ortho fused porphyrin decreases compared to that of the precursor. The HOMO and LUMO of the planar γ-ortho fused products are localized on the partially fused benzo moieties and the meso-position, respectively.

Construction of 2D extended cocrystals on the Au(111) surface via IOaldehyde halogen bonds.

2D extended organic cocrystals were constructed using 1,4-diiodotetrafluorobenzene and aromatic aldehydes via IOaldehyde halogen bonds on an Au(111) surface. The competition and synergy of halogen bonds and hydrogen bonds in 2D co-crystallization were revealed by scanning tunneling microscopy.

Radical Borylative Cyclization of 1,6-Dienes: Synthesis of Boron-Substituted Six-Membered Heterocycles and Carbocycles.

A radical borylative cyclization reaction of 1,6-dienes was developed to assemble boron-handled six-membered heterocycles and carbocycles. This reaction was initiated by the chemo- and regio-controlled addition of an N-heterocyclic carbene-boryl radical to one of the alkene tethers, followed by an intramolecular 6- exo cyclization to afford a six-membered ring framework. The utility of this method was demonstrated in the synthesis of diverse paroxetine analogues through late-stage derivatization of the boryl functional unit.

Relationship between levels of testosterone and cortisol in saliva and aggressive behaviors of adolescents / 生物医学与环境科学（英文）

<p><b>OBJECTIVE</b>To explore the endocrinal factors which influence the aggressive behavior of adolescents.</p><p><b>METHODS</b>The levels of cortisol (CORT), testosterone (T), prolactin (PRL), and growth hormone (GH) in saliva from 20 aggressive students and 20 non-aggressive control students were measured by radioimmunoassay (RIA). The students were matched for their gender, age, grade, stage of pubertal development, and economic status of their families.</p><p><b>RESULTS</b>The salivary T levels were 22.20 +/- 14.50 pg/mL and 19.54 +/- 12.52 pg/mL in aggressive male and female students, 13.20 +/- 6.85 pg/mL and 5.24 +/- 3.03 pg/mL in non-aggressive male and female students (P < 0.05). The male aggressive students had a lower level of CORT in saliva than non-aggressive male students (P < 0.05). There were no significant differences in the salivary levels of PRL or GH between the aggressive and non-aggressive groups. Correlation analysis revealed a negative relationship in male students between the salivary CORT levels and the aggression factor scores of the child behavior checklist (CBCL). In addition, the data also showed a positive relationship between the salivary T levels and the aggression factor scores of CBCL in female students. Multiple linear regression analysis showed that the salivary CORT level was an independent predictive factor for aggressive behaviors in adolescent boys. The higher the CORT level, the less aggressive the boys were.</p><p><b>CONCLUSION</b>CORT and T levels may play a certain role in adolescent aggressive behaviors.</p>

Study on self-consciousness of children with learning disabilities and related factors / 生物医学与环境科学（英文）

<p><b>OBJECTIVE</b>To study the self-consciousness of children with learning disabilities (LD) and to identify related factors.</p><p><b>METHODS</b>Five hundred and sixty pupils graded from 1 to 6 in an elementary school were investigated. According to the pupil rating scale revised screening for learning disabilities (PRS), combined Raven's test (CRT) and achievement of main courses, 35 of 560 pupils were diagnosed as LD children. Thirty-five children were selected from the average children and 35 from advanced children in academic achievement equally matched in class, gender, and age with LD children as control groups. The three groups were tested by Piers-Harris children's self-concept scale. Basic information of each subject was collected by self-made questionnaire.</p><p><b>RESULTS</b>Compared with the average and advanced children, LD children got significantly lower scores in self-concept scale. Based on logistic regression analysis, 3 factors were identified, including family income per month, single child and delivery model.</p><p><b>CONCLUSION</b>The results suggest that self-consciousness of children with LD is lower than that of normal children.</p>