437 research outputs found
Zinc calixarene complexes for the ring opening polymerization of cyclic esters
Reaction of Zn(CâFâ
)â·toluene (two equivalents) with 1,3-dipropoxy-p-tert-butyl-calix[4]arene (LÂčHâ) led to the isolation of the complex [{Zn(CâFâ
)}âLÂč] (1), whilst similar use of Zn(Me)â resulted in the known complex [{Zn(Me)}âLÂč] (2). Treatment of LÂčHâ with in situ prepared Zn{N(SiMeâ)â}â in refluxing toluene led to the isolation of the compound [(Na)ZnN(SiMeâ)âLÂč] (3). The stepwise reaction of LÂčHâ and sodium hydride, followed by ZnClâ and finally NaN(SiMeâ)â yielded the compound [Zn{N(SiMeâ)â}âLÂč] (4). The reaction between three equivalents of Zn(CâFâ
)â·toluene and oxacalix[3]arene (LÂČHâ) at room temperature formed the compound {[Zn(CâFâ
)]âLÂČ} (5); heating of 5 in acetonitrile caused the ring opening of the parent oxacalix[3]arene and rearrangement to afford the complex [(LÂČ)Znâ(CâFâ
)(R)(RH)OH]·5MeCN R = CâFâ
CHâ-(p-á”BuPhenolate-CHâOCHââ)ââp-á”BuPhenolate-CHâOâ»)Âłâ» (6). The molecular structures of the new complexes 1, 3 and 6, together with that of the known complex 2, whose solid state structure has not previously been reported, have been determined. Compounds 1, 3â5 have been screened for the ring opening polymerization (ROP) of Δ-caprolactone (Δ-CL) and rac-lactide. Compounds featuring a ZnâCâFâ
fragment were found to be poor ROP pre-catalysts as they did not react with benzyl alcohol to form an alkoxide. By contrast, compound 4, which contains a zinc silylamide linkage, was the most active of the zinc-based calix[4]arene compounds screened and was capable of ROP at ambient temperature with 65% conversion over 4 h
Effect of pregnancy planning and fertility treatment on cognitive outcomes in children at ages 3 and 5: longitudinal cohort study
Objective To investigate how pregnancy planning, time to conception, and infertility treatment influence cognitive development at ages 3 and 5
Ring opening polymerization of lactides and lactones by multimetallic alkyl zinc complexes derived from the acids PhâC(X)COâ2H (X = OH, NHâ )
The reaction of the dialkylzinc reagents RâZn with the acids 2,2-PhâC(X)(COâH), where X = NHâ, OH, i.e. 2,2âČ-diphenylglycine (dpgH) or benzilic acid (benzH2), in toluene at reflux temperature afforded the tetra-nuclear ring complexes [RZn(dpg)]â, where R = Me (1), Et (2), 2-CFâCâHâ (3), and 2,4,6-FâCâHâ (4); complex 2 has been previously reported. The crystal structures of 1·(2MeCN), 3 and 4·(4(CâHâ)·1.59(HâO)) are reported, along with that of the intermediate compound (2-CFâCâHâ)3B·MeCN and the known compound [ZnClâ(NCMe)â]. Complexes 1â4, together with the known complex [(ZnEt)â(ZnL)â(benz)â] (5; L = MeCN), have been screened, in the absence of benzyl alcohol, for their potential to act as catalysts for the ring opening polymerization (ROP) of Δ-caprolactone (Δ-CL), ÎŽ-valerolactone (ÎŽ-VL) and rac-lactide (rac-LA); the co-polymerization of Δ-CL with rac-LA was also studied. Complexes 3 and 4 bearing fluorinated aryls at zinc were found to afford the highest activities
Pillared two-dimensional metal-organic frameworks based on a lower-rim acid appended calix[4]arene
Solvothermal reactions of the lower-rim functionalized diacid calix[4]arene 25,27-bis(methoxycarboxylic acid)-26,28-dihydroxy-4-tert-butylcalix[4]arene (LHâ) with Zn(NOâ)ââą6HâO and the dipyridyl ligands 4,4/-bipyridyl (4,4/-bipy), 1,2-di(4-pyridyl)ethylene (DPE) or 4,4/-azopyridyl (4,4/-azopy) afforded a series of 2-D structures of the formulae {[Zn(4,4/-bipy)(L)]âą2ÂŒDEF}n (1), {[Znâ(L)(DPE)]âąDEF}n (2) and {[Zn(OHâ)â(L)(4,4/-azopy)]âąDEF}n (3) (DEF = diethylformamide)
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Mapping maternity care: the configuration of maternity care in England. Birthplace in England research programme
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The Birthplace in England national prospective cohort study: further analyses to enhance policy and service delivery decision-making for planned place of birth
Background: Evidence from the Birthplace in England Research Programme supported a policy of offering âlow riskâ women a choice of birth setting, but a number of unanswered questions remained.
Aims: This project aimed to provide further evidence to support the development and delivery of maternity services and inform womenâs choice of birth setting: specifically, to explore maternal and organisational factors associated with intervention, transfer and other outcomes in each birth setting in âlow riskâ and âhigher riskâ women.
Design: Five component studies using secondary analysis of the Birthplace prospective cohort study (studies 2â5) and ecological analysis of unit/NHS trust-level data (studies 1 and 5).
Setting: Obstetric units (OUs), alongside midwifery units (AMUs), freestanding midwifery units (FMUs) and planned home births in England.
Participants: Studies 1â4 focused on âlow riskâ women with âtermâ pregnancies planning vaginal birth in 43 AMUs (nâ=â16,573), in 53 FMUs (nâ=â11,210), at home in 147 NHS trusts (nâ=â16,632) and in a stratified, random sample of 36 OUs (nâ=â19,379) in 2008â10. Study 5 focused on women with pre-existing medical and obstetric risk factors (âhigher riskâ women).
Main outcome measures: Interventions (instrumental delivery, intrapartum caesarean section), a measure of low intervention (ânormal birthâ), a measure of spontaneous vaginal birth without complications (âstraightforward birthâ), transfer during labour and a composite measure of adverse perinatal outcome (âintrapartum-related mortality and morbidityâ or neonatal admission within 48 hours for >â48 hours). In studies 1 and 3, rates of intervention/maternal outcome and transfer were adjusted for maternal characteristics.
Analysis: We used (a) funnel plots to explore variation in rates of intervention/maternal outcome and transfer between units/trusts, (b) simple, weighted linear regression to evaluate associations between unit/trust characteristics and rates of intervention/maternal outcome and transfer, (c) multivariable Poisson regression to evaluate associations between planned place of birth, maternal characteristics and study outcomes, and (d) logistic regression to investigate associations between time of day/day of the week and study outcomes.
Results: Study 1 â unit-/trust-level variations in rates of interventions, transfer and maternal outcomes were not explained by differences in maternal characteristics. The magnitude of identified associations between unit/trust characteristics and intervention, transfer and outcome rates was generally small, but some aspects of configuration were associated with rates of transfer and intervention. Study 2 â âlow riskâ women planning non-OU birth had a reduced risk of intervention irrespective of ethnicity or area deprivation score. In nulliparous women planning non-OU birth the risk of intervention increased with increasing age, but women of all ages planning non-OU birth experienced a reduced risk of intervention. Study 3 â parity, maternal age, gestational age and âcomplicating conditionsâ identified at the start of care in labour were independently associated with variation in the risk of transfer in âlow riskâ women planning non-OU birth. Transfers did not vary by time of day/day of the week in any meaningful way. The duration of transfer from planned FMU and home births was around 50â60 minutes; transfers for âpotentially urgentâ reasons were quicker than transfers for ânon-urgentâ reasons. Study 4 â the occurrence of some interventions varied by time of the day/day of the week in âlow riskâ women planning OU birth. Study 5 â âhigher riskâ women planning birth in a non-OU setting had fewer risk factors than âhigher riskâ women planning OU birth and these risk factors were different. Compared with âlow riskâ women planning home birth, âhigher riskâ women planning home birth had a significantly increased risk of our composite adverse perinatal outcome measure. However, in âhigher riskâ women, the risk of this outcome was lower in planned home births than in planned OU births, even after adjustment for clinical risk factors.
Conclusions: Expansion in the capacity of non-OU intrapartum care could reduce intervention rates in âlow riskâ women, and the benefits of midwifery-led intrapartum care apply to all âlow riskâ women irrespective of age, ethnicity or area deprivation score. Intervention rates differ considerably between units, however, for reasons that are not understood. The impact of major changes in the configuration of maternity care on outcomes should be monitored and evaluated. The impact of non-clinical factors, including labour ward practices, staffing and skill mix and womenâs preferences and expectations, on intervention requires further investigation. All women planning non-OU birth should be informed of their chances of transfer and, in particular, older nulliparous women and those more than 1 week past their due date should be advised of their increased chances of transfer. No change in the guidance on planning place of birth for âhigher riskâ women is recommended, but research is required to evaluate the safety of planned AMU birth for women with selected relatively common risk factors.
Funding: The National Institute for Health Research Health Services and Delivery Research programme
Perinatal and maternal outcomes in planned home and obstetric unit births in women at âhigher riskâ of complications: secondary analysis of the Birthplace national prospective cohort study
Objective: To explore and compare perinatal and maternal outcomes in women at âhigher riskâ of complications planning home versus obstetric unit (OU) birth.
Design: Prospective cohort study.
Setting: OUs and planned home births in England.
Population: 8180 âhigher riskâ women in the Birthplace cohort.
Methods: We used Poisson regression to calculate relative risks adjusted for maternal characteristics. Sensitivity analyses explored possible effects of differences in risk between groups and alternative outcome measures.
Main outcome measures: Composite perinatal outcome measure encompassing âintrapartum related mortality and morbidityâ (intrapartum stillbirth, early neonatal death, neonatal encephalopathy, meconium aspiration syndrome, brachial plexus injury, fractured humerus or clavicle) and neonatal admission within 48 hours for more than 48 hours. Two composite maternal outcome measures capturing intrapartum interventions/adverse maternal outcomes and straightforward birth.
Results: The risk of âintrapartum related mortality and morbidityâ or neonatal admission for more than 48 hours was lower in planned home births than planned OU births [adjusted relative risks (RR) 0.50, 95% CI 0.31â0.81]. Adjustment for clinical risk factors did not materially affect this finding. The direction of effect was reversed for the more restricted outcome measure âintrapartum related mortality and morbidityâ (RR adjusted for parity 1.92, 95% CI 0.97â3.80). Maternal interventions were lower in planned home births.
Conclusions: The babies of âhigher riskâ women who plan birth in an OU appear more likely to be admitted to neonatal care than those whose mothers plan birth at home, but it is unclear if this reflects a real difference in morbidity. Rates of intrapartum related morbidity and mortality did not differ statistically significantly between settings at the 5% level but a larger study would be required to rule out a clinically important difference between the groups
Mass Measurement of P for Improved Type-I X-ray Burst Modeling
Light curves are the primary observable of type-I x-ray bursts. Computational
x-ray burst models must match simulations to observed light curves. Most of the
error in simulated curves comes from uncertainties in process reaction
rates, which can be reduced via precision mass measurements of
neutron-deficient isotopes in the process path. We perform a precise
atomic mass measurement of P and use this new measurement to update
existing type-I x-ray burst models to produce an improved light curve.
High-precision Penning trap mass spectrometry was used to determine the
atomic mass of P. Modules for Experiments in Stellar Astrophysics (MESA)
was then used to simulate x-ray bursts using a 1D multi-zone model to produce
updated light curves. The mass excess of P was measured to be
-670.7 0.6 keV, a fourteen-fold precision increase over the mass reported
in AME2020. The Si()P and reverse photodisintegration
reaction rates have been determined to a higher precision based on the new,
high precision mass measurement of P, and MESA light curves generated
using these rates. Changes in the mass of P seem to have minimal effect
on XRB light curves, even in burster systems tailored to maximize impact.
The mass of P does not play a significant role in x-ray burst light
curves. It is important to understand that more advanced models don't just
provide more precise results, but often qualitatively different ones. This
result brings us a step closer to being able to extract stellar parameters from
individual x-ray burst observations. In addition, the Isobaric Multiplet Mass
Equation (IMME) has been validated for the quartet, but only
after including a small, theoretically predicted cubic term and utilizing an
updated excitation energy for the isobaric analogue state of Si.Comment: 8 pages, 7 figure
Systematic study of trace radioactive impurities in candidate construction materials for EXO-200
The Enriched Xenon Observatory (EXO) will search for double beta decays of
136Xe. We report the results of a systematic study of trace concentrations of
radioactive impurities in a wide range of raw materials and finished parts
considered for use in the construction of EXO-200, the first stage of the EXO
experimental program. Analysis techniques employed, and described here, include
direct gamma counting, alpha counting, neutron activation analysis, and
high-sensitivity mass spectrometry.Comment: 32 pages, 6 figures. Expanded introduction, added missing table
entry. Accepted for publication in Nucl. Instrum. Meth.
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