541 research outputs found
Effect of Ring Size and Migratory Groups on [1,n] Suprafacial Shift Reactions. Confirmation of Aromatic and Antiaromatic Transition-State Character by Ring-Current Analysis
Suprafacial sigmatropic shift reactions of 5-substituted cyclopentadienes,
3-substituted cyclopropenes, and 7-substituted cycloheptatrienes have been studied
computationally at the MP2/6-31+G* level for structures and energetics, and using the
ipsocentric method at the CHF/6-31G** level to calculate current-density maps. The
hydrogen shifts in cyclopentadienes have a diatropic ring currents indicating aromatic,
cyclopentadienide anion character. This result stands in contrast to the fluorine shift in 5-
fluorocyclopentadiene which requires much more energy, and has a paratropic ring
current in the TS pointing to antiaromatic, cyclopentadienyl cation character. [1,3]
hydrogen shifts in cyclopropenes are very difficult, passing through transition states that
have an extended C-C bond. For 3-fluorocyclopropene the [1,3] fluorine shift is much
easier than the hydrogen shift. For 7-fluorocycloheptatriene the [1,7] hydrogen shift is
predicted, but requires very high energy and has a paratropic ring current and
antiaromatic character. The [1,7] suprafacial fluorine shift is relatively easy, having a TS
with cycloheptatrienyl cation character. Patterns of currents, and the reversal for H and F
migration, are rationalized by orbital analysis based on the ipsocentric method.
Calculated charges and structural features for reactants and transition states support these
conclusions
Reductive CâC Coupling from α,ÎČâUnsaturated Nitriles by Intercepting Keteniminates
We present an atomâeconomic strategy to catalytically generate and intercept nitrile anion equivalents using hydrogen transfer catalysis. Addition of α,ÎČâunsaturated nitriles to a pincerâbased RuâH complex affords structurally characterized ÎșâNâcoordinated keteniminates by selective 1,4âhydride transfer. When generated inâ
situ under catalytic hydrogenation conditions, electrophilic addition to the keteniminate was achieved using anhydrides to provide αâcyanoacetates in high yields. This work represents a new application of hydrogen transfer catalysis using α,ÎČâunsaturated nitriles for reductive CâC coupling reactions.An atomâeconomic strategy to catalytically generate and intercept nitrile anion equivalents by hydrogen transfer catalysis has been developed. Addition of α,ÎČâunsaturated nitriles to a pincerâbased RuâH complex affords keteniminates by selective 1,4âhydride transfer, which were employed in a net hydrogenative acylation reaction.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149503/1/anie201904530.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/149503/2/anie201904530-sup-0001-misc_information.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/149503/3/anie201904530_am.pd
Effects of cortisol and dexamethasone on insulin signalling pathways in skeletal muscle of the ovine fetus during late gestation.
Before birth, glucocorticoids retard growth, although the extent to which this is mediated by changes in insulin signalling pathways in the skeletal muscle of the fetus is unknown. The current study determined the effects of endogenous and synthetic glucocorticoid exposure on insulin signalling proteins in skeletal muscle of fetal sheep during late gestation. Experimental manipulation of fetal plasma glucocorticoid concentration was achieved by fetal cortisol infusion and maternal dexamethasone treatment. Cortisol infusion significantly increased muscle protein levels of Akt2 and phosphorylated Akt at Ser473, and decreased protein levels of phosphorylated forms of mTOR at Ser2448 and S6K at Thr389. Muscle GLUT4 protein expression was significantly higher in fetuses whose mothers were treated with dexamethasone compared to those treated with saline. There were no significant effects of glucocorticoid exposure on muscle protein abundance of IR-ÎČ, IGF-1R, PKCζ, Akt1, calpastatin or muscle glycogen content. The present study demonstrated that components of the insulin signalling pathway in skeletal muscle of the ovine fetus are influenced differentially by naturally occurring and synthetic glucocorticoids. These findings may provide a mechanism by which elevated concentrations of endogenous glucocorticoids retard fetal growth
Gas phase reactions of trimethyl borate with phosphates and their non-covalent complexes
5-HT2A and 5-HT2C receptors as hypothalamic targets of developmental programming in male rats.
Although obesity is a global epidemic, the physiological mechanisms involved are not well understood. Recent advances reveal that susceptibility to obesity can be programmed by maternal and neonatal nutrition. Specifically, a maternal low-protein diet during pregnancy causes decreased intrauterine growth, rapid postnatal catch-up growth and an increased risk for diet-induced obesity. Given that the synthesis of the neurotransmitter 5-hydroxytryptamine (5-HT) is nutritionally regulated and 5-HT is a trophic factor, we hypothesised that maternal diet influences fetal 5-HT exposure, which then influences development of the central appetite network and the subsequent efficacy of 5-HT to control energy balance in later life. Consistent with our hypothesis, pregnant rats fed a low-protein diet exhibited elevated serum levels of 5-HT, which was also evident in the placenta and fetal brains at embryonic day 16.5. This increase was associated with reduced levels of 5-HT2CR, the primary 5-HT receptor influencing appetite, in the fetal, neonatal and adult hypothalamus. As expected, a reduction of 5-HT2CR was associated with impaired sensitivity to 5-HT-mediated appetite suppression in adulthood. 5-HT primarily achieves effects on appetite by 5-HT2CR stimulation of pro-opiomelanocortin (POMC) peptides within the arcuate nucleus of the hypothalamus (ARC). We show that 5-HT2ARs are also anatomically positioned to influence the activity of ARC POMC neurons and that mRNA encoding 5-HT2AR is increased in the hypothalamus ofin uterogrowth-restricted offspring that underwent rapid postnatal catch-up growth. Furthermore, these animals at 3 months of age are more sensitive to appetite suppression induced by 5-HT2AR agonists. These findings not only reveal a 5-HT-mediated mechanism underlying the programming of susceptibility to obesity, but also provide a promising means to correct it, by treatment with a 5-HT2AR agonist
Manipulating the fragmentation patterns of phosphopeptides via gas-phase boron derivatization: Determining phosphorylation sites in peptides with multiple serines
Classroom Ventilation: The Effectiveness of Preheating and Refresh Breaks: An analysis of 169 spaces at 43 schools across New Zealand
The COVID-19 pandemic has highlighted the importance of ventilation as a transmission mitigation strategy. However,
there was a widely held concern that a drop in outdoor temperatures during winter may impact thermal comfort in the
context of naturally ventilated classrooms. This concern has not been widely investigated by peer-reviewed empirical
studies (Sutherland et al., 2022b).
The aim of the Ministryâs ventilation monitoring initiative was to assess ventilation performance and thermal comfort
by continuously measuring indoor CO2 levels, air temperature, and relative humidity in classrooms during winter,
without obstructing teaching activities.
A total of 43 schools, which represent a broad mix of property attributes and located across the 6 Climate Zones in New
Zealand, were selected for the monitoring initiative. The CO2 monitors were deployed in about 4-6 pre-selected and
representative spaces in each school. Data was retrieved from 213 spaces; of these, 44 spaces were excluded, because
the initiative concentrated on teaching environments (classrooms) and those spaces were categorised as non-teaching
environments (e.g., staff rooms, meeting rooms, etc.).
From the 213 spaces, the data from 169 teaching spaces retrieved for the period 23 May to 26 August 2022 were
analysed to ascertain the impacts of inferred human behaviours considered to be able to improve natural ventilation
and detected from features of CO2 and temperature data. This analysis does not (and did not intend to) corroborate
independent observation of behaviours
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