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Dissociation of molecular hydrogen (H2) is extensively studied to understand the mechanism of hydrogenation reactions. In this study, H2 dissociation by Au1-doped closed-shell titanium oxide cluster anions AuTi3O7− and AuTi3O8− has been identified by mass spectrometry and quantum chemistry calculations. The clusters were generated by laser ablation and mass-selected to react with H2 in an ion trap reactor. In the reaction of AuTi3O8− with H2, the ion pair Au+−O22− rather than Au+−O2− is the active site to promote H2 dissociation. This finding is in contrast with the previous result that the lattice oxygen is usually the reactive oxygen species in H2 dissociation. The higher reactivity of the peroxide species is further supported by frontier molecular orbital analysis. This study provides new insights into gold catalysis involving H2 activation and dissociation. [ABSTRACT FROM AUTHOR]

Time-of-flight mass spectrometry experiments demonstrated that laser ablation generated and mass selected gold-vanadium heteronuclear oxide cluster AuVO4+ can oxidize three H2 molecules consecutively in an ion trap reactor. Quantum chemistry calculations were employed to reveal the elementary steps involved in the consecutive H2 oxidation. The positively charged gold in AuVO4+ functions as the active site to capture H2 and split the H-H bond in collaboration with the terminal lattice oxygen O2−, during the process of which the superoxide species O2•− in AuVO4+ is activated and then dissociated to supply enough oxygen sites for the subsequent H2 oxidation. After the oxidation of three H2 molecules, the Au-O bond in AuVO4+ is converted to Au-V bond in product AuVO+ that is inert towards H2. In contast, cluster AuNbO4+ that is structurally related to AuVO4+ can oxdize only one H2 molecule. The origin of the different reactivities between two clusters was explored and the importance of different central metal in H2 oxidation was emphasized. [ABSTRACT FROM AUTHOR]

Time-of-flight mass spectrometry experiments demonstrated that laser ablation generated and mass selected gold-vanadium heteronuclear oxide cluster AuVO4+ can oxidize three H2 molecules consecutively in an ion trap reactor. Quantum chemistry calculations were employed to reveal the elementary steps involved in the consecutive H2 oxidation. The positively charged gold in AuVO4+ functions as the active site to capture H2 and split the H-H bond in collaboration with the terminal lattice oxygen O2−, during the process of which the superoxide species O2•− in AuVO4+ is activated and then dissociated to supply enough oxygen sites for the subsequent H2 oxidation. After the oxidation of three H2 molecules, the Au-O bond in AuVO4+ is converted to Au-V bond in product AuVO+ that is inert towards H2. In contast, cluster AuNbO4+ that is structurally related to AuVO4+ can oxdize only one H2 molecule. The origin of the different reactivities between two clusters was explored and the importance of different central metal in H2 oxidation was emphasized. [ABSTRACT FROM AUTHOR]

Background: The relationship between the number of harvested lymph nodes (HLNs) and prognosis of gastric cancer patients without an involvement of lymph nodes has not been well-evaluated. The objective of this study is to further explore this issue.Methods: We collected data from 399 gastric cancer patients between November 2006 and October 2011. All of them were without metastatic lymph nodes.Results: Survival analyses showed that statistically significant differences existed in the survival outcomes between the two groups allocated by the total number of HLNs ranging from 16 to 22. Therefore, we adopted 22 as the cut-off value of the total number of HLNs for grouping (group A: HLNs <22; group B: HLNs≥22). The intraoperative and postoperative characteristics, including operative blood loss (P=0.096), operation time (P=0.430), postoperative hospital stay (P=0.142), complications (P=0.552), rate of reoperation (P=0.966) and postoperative mortality (P=1.000), were comparable between the two groups. T-stage-stratified Kaplan-Meier analyses revealed that the 5-year survival rate of patients at the T4 stage was better in group B than in group A (76.9% vs. 58.5%; P=0.004). An analysis of multiple factors elucidated that the total number of HLNs, T stage, operation time and age were independently correlated factors of prognosis.Conclusions: Regarding gastric cancer patients without the involvement of lymph nodes, an HLN number ≥22 would be helpful in prolonging their overall survival, especially for those at T4 stage. The total number of HLNs was an independent prognostic factor for this population of patients. [ABSTRACT FROM AUTHOR]

Background: The optimal extent of gastrectomy for middle-third gastric cancer remains controversial. In our study, the short-term effects and longer-term survival outcomes of distal subtotal gastrectomy and total gastrectomy are analysed to determine the optimal extent of gastrectomy for middle-third gastric cancer.Methods: We retrospectively collect and analyse clinicopathologic data and follow-up outcomes from a prospectively collected database at the Peking University Cancer Hospital. Patients with middle-third gastric adenocarcinoma who underwent curative resection are enrolled in our study.Results: We collect data of 339 patients between January 2005 and October 2011. A total of 144 patients underwent distal subtotal gastrectomy, and 195 patients underwent total gastrectomy. Patients in the total gastrectomy group have longer operative duration (P < 0.001) and postoperative hospital stay (P = 0.001) than those in the distal subtotal gastrectomy group. In the total gastrectomy group, more lymph nodes are harvested (P < 0.001). Meanwhile, the rate of postoperative complications is lower in the distal subtotal gastrectomy group than in the total gastrectomy group (8% vs 15%, P = 0.047). Further analysis demonstrates that the rate of anastomosis leakage is lower in the distal subtotal gastrectomy group than in the total gastrectomy group (0% vs 4%, P = 0.023). Kaplan-Meier (log rank test) analysis shows a significant difference in overall survival between the two groups. The 5-year overall survival rates in the distal subtotal gastrectomy and total gastrectomy groups are 65% and 47%, respectively (P < 0.001). Further stage-stratified analysis reveals that no statistical significance exists in 5-year survival rate between the distal subtotal gastrectomy and total gastrectomy groups at the same stage. Multivariate analysis shows that age (P = 0.046), operation duration (P < 0.001), complications (P = 0.037), usage of neoadjuvant chemotherapy (P < 0.001), tumor size (P = 0.012), presence of lymphovascular invasion (P = 0.043) and N stage (P < 0.001) are independent prognostic factors for survival.Conclusions: For patients with middle-third gastric cancer, distal subtotal gastrectomy shortens the operation duration and postoperative hospital stay and reduces postoperative complications. Meanwhile, the long-term survival of patients with distal subtotal gastrectomy is similar to that of those with total gastrectomy at the same stage. The extent of gastrectomy for middle-third gastric cancer is not an independent prognostic factor for survival. [ABSTRACT FROM AUTHOR]

Time-of-flight mass spectrometry experiments demonstrated that laser ablation generated and mass selected Au2TiO4− cluster anions can unexpectedly oxidize three CO molecules in an ion trap reactor. This is an improvement on the more commonly observed oxidation of at most two CO molecules by a doped cluster. Quantum chemistry calculations were performed to rationalize the reactions. The lowest energy isomer of Au2TiO4− contains a superoxide unit, the participation of which in CO oxidation can be promoted by the Au2 dimer. The Au2 dimer functions as a rather flexible electron reservoir in each CO oxidation step in terms of the release and storage of electrons to drive the dissociation of superoxide to peroxide and then to lattice oxygen atoms, which can be removed by reaction with CO molecules. This gas-phase study enriches our understanding toward the nature of reactive oxygen species involved in gold-catalyzed oxidation reactions. [ABSTRACT FROM AUTHOR]

Atomic clusters are being actively studied for activation of methane, the most stable alkane molecule. While many cluster cations are very reactive with methane, the cluster anions are usually not very reactive, particularly for noble metal free anions. This study reports that the reactivity of molybdenum carbide cluster anions with methane can be much enhanced by adsorption of CO. The Mo2C2− is inert with CH4 while the CO addition product Mo2C3O− brings about dehydrogenation of CH4 under thermal collision conditions. The cluster structures and reactions are characterized by mass spectrometry, photoelectron spectroscopy, and quantum chemistry calculations, which demonstrate that the Mo2C3O− isomer with dissociated CO is reactive but the one with non-dissociated CO is unreactive. The enhancement of cluster reactivity promoted by CO adsorption in this study is compared with those of reported systems of a few carbonyl complexes. [ABSTRACT FROM AUTHOR]

The study of chemical reactions between gold-containing heteronuclear oxide clusters and small molecules can provide molecular level mechanisms to understand the excellent activity of gold supported by metal oxides. While the promotion role of gold in alkane transformation was identified in the clusters with atomic oxygen radicals (O−.), the role of gold in the systems without O−. is not clear. By employing mass spectrometry and quantum chemistry calculations, the reactivity of Au2VO3+ clusters with closed-shell electronic structures toward ethane was explored. Both the dehydrogenation and ethene elimination channels were identified. It is gold rather than oxygen species initiating the C−H activation. The Au−Au dimer formed during the reactions plays important roles in ethane transformation. The reactivity comparison between Au2VO3+ and bare Au2+ demonstrates that Au2VO3+ not only retains the property of bare Au2+ that transforming ethane to dihydrogen, but also exhibits new functions in converting ethane to ethene, which reveals the importance of the composite system. This study provides a further understanding of the reactivity of metal oxide supported gold in alkane activation and transformation. [ABSTRACT FROM AUTHOR]

Although early transition metal (ETM) carbides can activate CH bonds in condensed-phase systems, the electronic-level mechanism is unclear. Atomic clusters are ideal model systems for understanding the mechanisms of bond activation. For the first time, CH activation of a simple alkane (ethane) by an ETM carbide cluster anion (MoC3−) under thermal-collision conditions has been identified by using high-resolution mass spectrometry, photoelectron imaging spectroscopy, and high-level quantum chemical calculations. Dehydrogenation and ethene elimination were observed in the reaction of MoC3− with C2H6. The CH activation follows a mechanism of oxidative addition that is much more favorable in the carbon-stabilized low-spin ground electronic state than in the high-spin excited state. The reaction efficiency between the MoC3− anion and C2H6 is low (0.23±0.05) %. A comparison between the anionic and a highly efficient cationic reaction system (Pt++C2H6) was made. It turned out that the potential-energy surfaces for the entrance channels of the anionic and cationic reaction systems can be very different. [ABSTRACT FROM AUTHOR]

Although early transition metal (ETM) carbides can activate CH bonds in condensed-phase systems, the electronic-level mechanism is unclear. Atomic clusters are ideal model systems for understanding the mechanisms of bond activation. For the first time, CH activation of a simple alkane (ethane) by an ETM carbide cluster anion (MoC3−) under thermal-collision conditions has been identified by using high-resolution mass spectrometry, photoelectron imaging spectroscopy, and high-level quantum chemical calculations. Dehydrogenation and ethene elimination were observed in the reaction of MoC3− with C2H6. The CH activation follows a mechanism of oxidative addition that is much more favorable in the carbon-stabilized low-spin ground electronic state than in the high-spin excited state. The reaction efficiency between the MoC3− anion and C2H6 is low (0.23±0.05) %. A comparison between the anionic and a highly efficient cationic reaction system (Pt++C2H6) was made. It turned out that the potential-energy surfaces for the entrance channels of the anionic and cationic reaction systems can be very different. [ABSTRACT FROM AUTHOR]