Synthesis of main group, rare-earth, and d{sup 0} metal complexes containing beta-hydrogen

A series of organometallic compounds containing the tris(dimethylsilyl)methyl ligand are described. The potassium carbanions KC(SiHMe{sub 2}){sub 3} and KC(SiHMe{sub 2}){sub 3}TMEDA are synthesized by deprotonation of the hydrocarbon HC(SiHMe{sub 2}){sub 3} with potassium benzyl. KC(SiHMe{sub 2}){sub 3}TMEDA crystallizes as a dimer with two types of three-center-two-electron KH- Si interactions. Homoleptic Ln(III) tris(silylalkyl) complexes containing β-SiH groups M{C(SiHMe{sub 2}){sub 3}}{sub 3} (Ln = Y, Lu, La) are synthesized from salt elimination of the corresponding lanthanide halide and 3 equiv. of KC(SiHMe{sub 2}){sub 3}. The related reactions with Sc yield bis(silylalkyl) ate-complexes containing either LiCl or KCl. The divalent calcium and ytterbium compounds M{C(SiHMe{sub 2}){sub 3}}{sub 2}L (M = Ca, Yb; L = THF{sub 2} or TMEDA) are prepared from MI{sub 2} and 2 equiv of KC(SiHMe{sub 2}){sub 3}. The compounds M{C(SiHMe{sub 2}){sub 3}}{sub 2}L (M = Ca, Yb; L = THF{sub 2} or TMEDA) and La{C(SiHMe{sub 2}){sub 3}}{sub 3} react with 1 equiv of B(C{sub 6}F{sub 5}){sub 3} to give 1,3- disilacyclobutane {Me2Si-C(SiHMe2)2}2 and MC(SiHMe2)3HB(C6F5)3L, and La{C(SiHMe{sub 2}){sub 3}}{sub 2}HB(C{sub 6}F{sub 5}){sub 3}, respectively. The corresponding reactions of Ln{C(SiHMe{sub 2}){sub 3}}{sub 3} (Ln = Y, Lu) give the β-SiH abstraction product [{(Me{sub 2}HSi){sub 3}C}{sub 2}LnC(SiHMe{sub 2}){sub 2}SiMe{sub 2}][HB(C{sub 6}F{sub 5}){sub 3}] (Ln = Y, Lu), but the silene remains associated with the Y or Lu center. The abstraction reactions of M{C(SiHMe{sub 2}){sub 3}}{sub 2}L (M = Ca, Yb; L = THF{sub 2 }or TMEDA) and Ln{C(SiHMe{sub 2}){sub 3}}{sub 3} (Ln = Y, Lu, La) and 2 equiv of B(C{sub 6}F{sub 5}){sub 3} give the expected dicationic M{HB(C{sub 6}F{sub 5}){sub 3}}{sub 2}L (M = Ca, Yb; L = THF{sub 2} or TMEDA) and dicationic mono(silylalkyl) LnC(SiHMe{sub 2}){sub 3}{HB(C{sub 6}F{sub 5}){sub 3}}{sub 2} (Ln = Y, Lu, La), respectively. Salt metathesis reactions of Cp{sub 2}(NR{sub 2})ZrX (X = Cl, I, OTf; R = t-Bu, SiHMe{sub 2}) and lithium hydrosilazide ultimately afford hydride products Cp{sub 2}(NR{sub 2})ZrH that suggest unusual β-hydrogen elimination processes. A likely intermediate in one of these reactions, Cp{sub 2}Zr[N(SiHMe{sub 2})t-Bu][N(SiHMe{sub 2}){sub 2}], is isolated under controlled synthetic conditions. Addition of alkali metal salts to this zirconium hydrosilazide compound produces the corresponding zirconium hydride. However as conditions are varied, a number of other pathways are also accessible, including C-H/Si-H dehydrocoupling, γ-abstraction of a CH, and β-abstraction of a SiH. Our observations suggest that the conversion of (hydrosilazido)zirconocene to zirconium hydride does not follow the classical four-center β- elimination mechanism. Elimination and abstraction reactions dominate the chemistry of ligands containing β- hydrogen. In contrast, Cp{sub 2}Zr{N(SiHMe{sub 2}){sub 2}}H and Cp{sub 2}Zr{N(SiHMe{sub 2}){sub 2}}Me undergo selective γ-CH bond activation to yield the azasilazirconacycle Cp{sub 2Zr}{κ{sup 2}-N(SiHMe{sub 2})SiHMeCH{sub 2}}, even though there are reactive β-hydrogen available for abstraction. The β-SiH groups in metallacycle provide access to new pathways for sixteen-electron zirconium alkyl compounds, in which Cp{sub 2}Zr{κ{sup 2}-N(SiHMe{sub 2})SiHMeCH{sub 2}} undergoes a rare σ-bond metathesis reaction with ethylene. The resulting vinyl intermediate undergoes β-hydrogen abstraction to reform ethylene and a silanimine zirconium species that reacts with ethylene to give a metallacyclopentane as the isolated product. The pendent β-SiH in metallocycle also reacts with paraformaldehyde through an uncatalyzed hydrosilylation to form an exocyclic methoxysilyl moiety, while the zirconium-carbon bond in metallocycle is surprisingly inert toward formaldehyde. Still, the Zr-C moiety in metallocycle is available for chemistry, and it interacts with the carbon monoxide and strong electrophile B(C{sub 6}F{sub 5}){sub 3} to provide Cp{sub 2}Zr[κ{sup 2}- OC(=CH{sub 2})SiMeHN(SiHMe{sub 2})] and Cp{sub 2}Zr[N(SiHMe{sub 2})SiHMeCH{sub 2}B(C{sub 6}F{sub 5}){sub 3}]. Finally, the frustrated Lewis-pair 2,6-lutidine-B(C{sub 6}F{sub 5}){sub 3} adduct reacts with the intra-cyclic SiH to give a transient 2,6-lutidine-stabilized silicon cation [Cp{sub 2}ZrCH{sub 2}SiMe(2,6-Me{sub 2 }- NC{sub 6}H{sub 3})N(SiMe{sub 2}H)][HB(C{sub 6}F{sub 5}){sub 3}] that slowly rearranges to give Cp{sub 2}Zr[N(SiHMe{sub 2})SiHMeCH{sub 2}B(C{sub 6}F{sub 5}){sub 3}] and free 2,6-lutidine. Finally, we also demonstrated a β-elimination of a cationic zirconocene disilazide compound [Cp{sub 2}ZrN(SiHMe{sub 2}){sub 2}]{sup +} that is facilitated by DMAP (4-N,N-dimethylaminopyridine) to give [Cp{sub 2}ZrH{N(SiHMe{sub 2})(SiMe{sub 2DMAP})}]{sup +}. A formal insertion reaction of a Zr-R group of Cp{sub 2}ZrN(SiHMe{sub 2}){sub 2}R (R = H, alkyl, halide, alkoxide) into a silaimine, formed by reaction of the zirconocene silazide and B(C{sub 6}F{sub 5}){sub 3}, to give [Cp{sub 2}Zr{N(SiHMe{sub 2})(SiRMe{sub 2})]{sup +}. Thus, we also show the application of the β-elimination reaction in hydrosilylation of ketones and aldehydes

Senior year = 高三

Film Director: Zhou Hao (周浩) Film Release Year: 2005https://commons.ln.edu.hk/ccs_worksheet/1008/thumbnail.jp

Perceptions of Special School Nurses in Hong Kong During the COVID-19 Pandemic

AbstractIntroduction: The coronavirus (COVID-19) pandemic is a global public health crisis that started in 2020. Although health authorities believe that reducing social contact between students is necessary to protect students’ health, there is limited research on the lived experiences of school nurses caring for children and adolescents with intellectual disabilities (ID) in special schools during the COVID-19 pandemic. The aim of this study was to explore the experiences of school nurses caring for children and adolescents with ID in Hong Kong.Methods: This study used a phenomenological research design focused on experiences, events, and occurrences. Nine school nurses working in special schools in Hong Kong shared their lived experiences of caring for students with ID during the COVID-19 pandemic. Transcripts were analyzed according to the steps in Colaizzi’s method to understand and accurately describe the experiences of school nurses.Results: The role of school nurses during the COVID-19 pandemic was complex and multi-dimensional. Three themes emerged from the interview data: (1) the unpredictable and uncertain situation of COVID-19, (2) the extreme emotions experienced while caring for students during the outbreak of COVID-19, and (3) the inevitability of committing nursing errors during the outbreak of COVID-19.Conclusions: This study provided first-hand insights into nurses’ experiences in caring for students with special health needs during the COVID-19 pandemic. The findings indicated that continuous support from school organizations is needed to enable school nurses to care for students and their parents during a public health crisis, and to help school nurses to cope with unpredictable situations

The use of commitment techniques to support weight loss maintenance in obese adolescents

Objectives: Obesity is a rising problem in adolescents related to unhealthy behaviours. Commitment devises are one type of behavioural intervention that may help people change their behaviours. The current pilot trial tests whether commitment devices delivered via text message help adolescents maintain their recent weight loss. Methods: During a 12-week pilot trial adolescents who attended a weight loss camp were randomly assigned to either received text messages that contained only information, i.e., advice, about weight loss management (n=13) or asked for them to commit to following the same advise (n=14). Results: The BMI of the adolescents in the commitment group did not change. In contrast, the BMI of adolescents in the information group increased. A linear regression revealed that group was a significant predictor of BMI change. A logistic regression revealed that adolescents in the information group were nearly eight times more likely to regain weight than those in the commitment group. Conclusions: This is the first study with adolescents to show weight maintenance using a commitment device. The results suggest that commitment devices can help adolescents maintain their recent weight loss

Appetite, gut hormone and energy intake responses to low volume sprint interval and traditional endurance exercise.

Sprint interval exercise improves several health markers but the appetite and energy balance response is unknown. This study compared the effects of sprint interval and endurance exercise on appetite, energy intake and gut hormone responses. Twelve healthy males [mean (SD): age 23 (3) years, body mass index 24.2 (2.9) kg m(-2), maximum oxygen uptake 46.3 (10.2) mL kg(-1) min(-1)] completed three 8 h trials [control (CON), endurance exercise (END), sprint interval exercise (SIE)] separated by 1 week. Trials commenced upon completion of a standardised breakfast. Sixty minutes of cycling at 68.1 (4.3) % of maximum oxygen uptake was performed from 1.75-2.75 h in END. Six 30-s Wingate tests were performed from 2.25-2.75 h in SIE. Appetite ratings, acylated ghrelin and peptide YY (PYY) concentrations were measured throughout each trial. Food intake was monitored from buffet meals at 3.5 and 7 h and an overnight food bag. Appetite (P 0.05). Therefore, relative energy intake (energy intake minus the net energy expenditure of exercise) was lower in END than that in CON (15.7 %; P = 0.006) and SIE (11.5 %; P = 0.082). An acute bout of endurance exercise resulted in lower appetite perceptions in the hours after exercise than sprint interval exercise and induced a greater 24 h energy deficit due to higher energy expenditure during exercise

Improvement of Insulin Sensitivity by Isoenergy High Carbohydrate Traditional Asian Diet: A Randomized Controlled Pilot Feasibility Study

The prevalence of diabetes is rising dramatically among Asians, with increased consumption of the typical Western diet as one possible cause. We explored the metabolic responses in East Asian Americans (AA) and Caucasian Americans (CA) when transitioning from a traditional Asian diet (TAD) to a typical Western diet (TWD), which has not been reported before. This 16-week randomized control pilot feasibility study, included 28AA and 22CA who were at risk of developing type 2 diabetes. Eight weeks of TAD were provided to all participants, followed by 8 weeks of isoenergy TWD (intervention) or TAD (control). Anthropometric measures, lipid profile, insulin resistance and inflammatory markers were assessed. While on TAD, both AA and CA improved in insulin AUC (−960.2 µU/mL×h, P = 0.001) and reduced in weight (−1.6 kg; P<0.001), body fat (−1.7%, P<0.001) and trunk fat (−2.2%, P<0.001). Comparing changes from TAD to TWD, AA had a smaller weight gain (−1.8 to 0.3 kg, P<0.001) than CA (−1.4 to 0.9 kg, P = 0.001), but a greater increase in insulin AUC (AA: −1402.4 to 606.2 µU/mL×h, P = 0.015 vs CA: −466.0 to 223.5 µU/mL×h, P = 0.034) and homeostatic static model assessment-insulin resistance (HOMA-IR) (AA: −0.3 to 0.2, P = 0.042 vs CA: −0.1 to 0.0, P = 0.221). Despite efforts to maintain isoenergy state and consumption of similar energy, TAD induced weight loss and improved insulin sensitivity in both groups, while TWD worsened the metabolic profile. Trial Registration: ClinicalTrials.gov NCT0037954

Bridging flavour violation and leptogenesis in SU(3) family models

We reconsider basic, in the sense of minimal field content, Pati-Salam x SU(3) family models which make use of the Type I see-saw mechanism to reproduce the observed mixing and mass spectrum in the neutrino sector. The goal of this is to achieve the observed baryon asymmetry through the thermal decay of the lightest right-handed neutrino and at the same time to be consistent with the expected experimental lepton flavour violation sensitivity. This kind of models have been previously considered but it was not possible to achieve a compatibility among all of the ingredients mentioned above. We describe then how different SU(3) messengers, the heavy fields that decouple and produce the right form of the Yukawa couplings together with the scalars breaking the SU(3) symmetry, can lead to different Yukawa couplings. This in turn implies different consequences for flavour violation couplings and conditions for realizing the right amount of baryon asymmetry through the decay of the lightest right-handed neutrino. Also a highlight of the present work is a new fit of the Yukawa textures traditionally embedded in SU(3) family models.Comment: 26 pages, 5 figures, Some typos correcte

Examining the Drinking Motives Questionnaire-Revised Short Form among university students in Australia, New Zealand and Argentina

CAUL read and publish agreement 2023fals

A link between tropical intraseasonal variability and Arctic stratospheric ozone

Previous studies using satellite measurements showed evidence that subtropical upper troposphere/lower stratosphere ozone (O_3) can be modulated by tropical intraseasonal variability, the most dominant form of which is the Madden Julian Oscillation (MJO) with a period of 30–60 days. Here we further study the MJO modulation in the upper troposphere/lower stratosphere O_3 over the northern extratropics and the Arctic. Significant MJO-related O_3 signals (13–20 Dobson units) are found over the northern extratropics (north of 30°N). The O_3 anomalies change their magnitude and patterns depending on the phase of the MJO. Over the Arctic, the MJO-related O_3 anomalies are dominated by a wave number 2 structure and are anticorrelated with the geopotential height (GPH) anomalies at 250 hPa. The latter is similar to the findings in the previous studies over subtropics and indicates that the Arctic upper troposphere/lower stratosphere O_3 anomalies are associated with dynamical motions near the tropopause. The teleconnection from the tropics to the Arctic is likely through propagation of planetary waves generated by the equatorial heating that affects the tropopause height and O_3 at high latitudes