A theoretical study of the oxidation of benzene by manganese oxide clusters: formation of quinone intermediates.

Manganese oxides (MnxOy) have been widely applied in various chemical industrial processes owing to their long lifetime, low cost and high abundance. They have been used as co-reactants for the elimination of volatile organic compounds (VOCs); however, their oxidation mechanism is not clearly established. In this theoretical study, interaction capacities between benzene (C6H6) and MnxOy clusters, which were modeled with MnO2 and Mn2O3 molecules, were investigated by quantum chemical computations using density functional theory (DFT) with the PBE-D3 functional. The interaction capacity between C6H6 and MnxOy was evaluated, and the probing of the initial stage of the C6H6 oxidation at a molecular level offers an in-depth oxidation reaction path. Interaction energies computed in several spin states, along with the analysis of the electron distribution using the quantum theory of atoms in molecules, natural bond orbital and Wiberg bond index techniques as well as local softness values and MO energies of fragments, point out that the interaction between C6H6 and Mn2O3 is stronger than that with MnO2, amounting to -43 and -35 kcal mol-1, respectively, and the metal atom is identified as the primary active site. During the oxide cluster-assisted oxidation, benzene firstly undergoes an oxidation reaction by active oxygen to generate intermediates such as hydroquinone and benzoquinone. The pathway involving p-benzoquinone as the product (noted as PR1) is the most energetically favored one through a transition structure lying at 19 kcal mol-1, below the energy reference of the reactants, leading to an energy barrier significantly lower than that of 36 kcal mol-1 found for the gas phase oxidation reaction with molecular oxygen without the assistance of the oxide clusters. Potential energy profiles illustrating the reaction paths and molecular mechanisms were described in detail.

Mechanistic insights into the dehydrogenation of formaldehyde, formic acid and methanol using the Pt4 cluster as a promising catalyst.

Reaction mechanisms of the dehydrogenation of formaldehyde, formic acid and methanol on the Pt4 cluster were computationally investigated using density functional theory (DFT) with the B3LYP functional in the conjunction with the aug-cc-pVTZ basis sets for H, C and O atoms, and the cc-pVDZ-PP basis set for Pt. Herein, the key mechanistic aspects of three possible pathways of the dehydrogenation of these compounds are summarized. The results indicate that the formation of H2 and CO or CO2 molecules is more energetically favorable than the generation of H and H2O, HCHO products. Generally, the formation of H2 molecule in the presence of catalysts is more favorable than the direct decomposition of either HCHO, HCOOH or CH3OH molecule. The use of Pt4 catalyst significantly reduces the energy barriers for C-H and O-H bond cleavage of all three compounds to 14, 9 and 12 kcal/mol, respectively. The decomposition of HCOOH is found to be the most energetically favorable. In addition, the mechanistic insights of the reactions confirm the reduction of the energy barriers of the gas-phase dehydrogenation by 67-82 kcal/mol and bring it to the values smaller than 14 kcal/mol in the presence of the Pt4 catalysts.

Patterns of risk for anxiety-depression amongst Vietnamese-immigrants: a comparison with source and host populations.

BACKGROUND: Studies suggest that immigrants have higher rates of anxiety-depression than compatriots in low-middle income countries and lower rates than populations in host high income countries. Elucidating the factors that underlie these stepwise variations in prevalence may throw new light on the pathogenesis of anxiety-depressive disorders globally. This study aimed to examine whether quantitative differences in exposure to, or the interaction between, risk factors account for these anxiety-depression prevalence differences amongst immigrant relative to source and host country populations. METHODS: Multistage population mental health surveys were conducted in three groups: 1) a Vietnamese-immigrant sample settled in Australia (n = 1161); 2) a Vietnamese source country sample residing in the Mekong Delta region (n = 3039); 3) an Australian-born host country sample (n = 7964). Multivariable logistic regression analyses compared risk factors between the Vietnamese-immigrant group and: 1) the Mekong Delta Vietnamese; and 2) the Australian-born group. Twelve month anxiety-depression diagnoses were the main outcome measures, derived from the Composite International Diagnostic Interview (CIDI), supplemented by an indigenously derived measure - the Phan Vietnamese Psychiatric Scale (PVPS) in both Vietnamese groups. RESULTS: The 12-month prevalence of anxiety-depression showed a stepwise increase across groups: Mekong Delta Vietnamese 4.8%; Vietnamese-immigrants 7.0%; Australian-born 10.2%. The two Vietnamese populations showed a similar risk profile with older age, exposure to potentially traumatic events (PTEs), multiple physical illnesses and substance use disorder (SUD) being associated with anxiety-depression, with the older Vietnamese-immigrants reporting greater exposure to these factors. The interaction between key risk factors differed fundamentally when comparing Vietnamese-immigrant and Australian-born samples. Age emerged as the major discriminator, with young Vietnamese-immigrants exhibiting particularly low rates of anxiety-depression. CONCLUSIONS: The findings reported here suggest that core risk factors for anxiety-depression may be universal, but their patterning and interaction may differ according to country-of-origin. The study also highlights the importance of including both standard international and culturally-specific measures to index cross-cultural manifestations of common mental disorders.

International and indigenous diagnoses of mental disorder among Vietnamese living in Vietnam and Australia.

BACKGROUND: Whether the prevalence rates of common mental disorders can be compared across countries depends on the cultural validity of the diagnostic measures used. AIMS: To investigate the prevalence of Western and indigenously defined mental disorders among Vietnamese living in Vietnam and in Australia, comparing the data with an Australian-born sample. METHOD: Comparative analysis of three multistage population surveys, including samples drawn from a community living in the Mekong Delta region of Vietnam (n=3039), Vietnamese immigrants residing in New South Wales, Australia (n=1161), and an Australian-born population (n=7961). Western-defined mental disorders were assessed by the Composite International Diagnostic Interview (CIDI) 2.0 and included DSM-IV anxiety, mood and substance use disorders as well as the ICD-10 category of neurasthenia. The Vietnamese surveys also applied the indigenously based Phan Vietnamese Psychiatric Scale (PVPS). Functional impairment and service use were assessed. RESULTS: The prevalence of CIDI mental disorders for Mekong Delta Vietnamese was 1.8% compared with 6.1% for Australian Vietnamese and 16.7% for Australians. Inclusion of PVPS mental disorders increased the prevalence rates to 8.8% for Mekong Delta Vietnamese and 11.7% for Australian Vietnamese. Concordance was moderate to good between the CIDI and the PVPS for Australian Vietnamese (area under the curve (AUC)=0.77) but low for Mekong Vietnamese (AUC=0.59). PVPS- and CIDI-defined mental disorders were associated with similar levels of functional impairment. CONCLUSIONS: Cultural factors in the expression of mental distress may influence the prevalence rates of mental disorders reported across countries. The findings have implications for assessing mental health needs at an international level.