Ling-Wei Chen

Synergism between Cu and Zn sites in Cu/Zn catalysts for methanol synthesis

Abstract Three Cu-based catalysts prepared using RF plasma-sputtering (Cu/ZnO and Cu/Al2O3) and coprecipitation (Cu/Zn/Al oxide) methods were employed for the investigation of the synergism between Cu and Zn sites. The static secondary ion mass spectrometry (SIMS) experiments indicate that, on both Cu/ZnO/Al2O3 and Cu/ZnO catalysts, CO is adsorbed at Cu sites (SIMS peaks appear at 91 and 93 amu), and H is bound to ZnO sites (67, 69, 70, 71 and 81, 83, 84, 85 amu) when the catalyst surfaces are exposed to H2, CO and CO2. Methoxy, the intermediate species of methanol synthesis, is found to be bound at Zn sites (95, 97, 98, 99 amu). CO and CO2 are found to induce Zn migration from sub-layers to the topmost layer while H2 is heterolyzed easier due to the presence of Cu. The coexistence of ZnO with Cu could enhance the capability of Cu to adsorb CO species and itself to adsorb H2 species. Al2O3 shows no synergetic effect with Cu in this experiment. No CO and H2 are detected on the Cu/Al2O3 catalyst exposed to syngas. The synergetic effect between Cu and Zn in the course of methanol synthesis was discussed.

Maternal caffeine intake during pregnancy is associated with risk of low birth weight: a systematic review and dose–response meta-analysis

BackgroundConsiderable controversy exists regarding the relation between maternal caffeine intake during pregnancy and risk of low birth weight (birth weight <2,500 g). We aim to assess this association using a systematic review and dose-response meta-analysis of prospective studies.MethodsPotential articles were identified by searching MEDLINE and SCOPUS databases through 17 July 2013. Two authors independently extracted information on study design, participant characteristics and estimates of associations. Random-effects models were used to derive the summary relative risks (RRs) and corresponding 95% confidence intervals (CIs). Dose-response relationships were assessed using generalized least-squares trend estimation.ResultsIn our meta-analysis, we included 13 prospective studies: 9 with low birth weight as a binary outcome variable (90,747 participants and 6,303 cases) and 6 with birth weight as a continuous outcome variable (10,015 participants; 2 studies reported both types of outcomes). Compared with the reference category with no or very low caffeine intake, the RR (95% CI) of low birth weight was 1.13 (1.06 to 1.21; I2 0.0%) for low intake (50 to 149 mg/day), 1.38 (1.18 to 1.62; I2 31.9%) for moderate intake (150 to 349 mg/day), and 1.60 (1.24 to 2.08; I2 65.8%) for high intake (≥350 mg/day). In the dose-response analysis, each 100-mg/day increment in maternal caffeine intake (around one cup of coffee) was associated with 13% (RR 1.13, 1.06 to 1.21) higher risk of low birth weight. The association persisted in strata defined according to various study characteristics. Moderate (-33 g, 95% CI -63 to -4; I2 0.3%) and high (-69 g, 95% CI -102 to -35; I2 0.0%) caffeine intakes were also associated with a significantly lower birth weight as compared with the reference category.ConclusionsHigher maternal caffeine intake during pregnancy was associated with a higher risk of delivering low birth weight infants. These findings support recommendations to restrict caffeine intake during pregnancy to low levels.

N2O decomposition over ZrO2 : an in-situ DRIFT, TPR, TPD and XPS study

Abstract The adsorption and decomposition of N2O over ZrO2 are studied using in-situ DRIFT, TPD, TPR and XPS. N2O is found to be reversibly and molecularly adsorbed on the surface. The dissociation of N2O into adsorbed dinitrogen and oxygen can take place on Ar-pre-purged ZrO2. The adsorbed dinitrogen, which produces an IR band at 2360 cm−1 as detected by in-situ DRIFT, can be easily removed from the surface by Ar-purge or heating to high temperatures. The adsorbed oxygen, which is identified by the IR band at 810 cm−1, is strongly bonded to surface Zr ions and remain at the surface at high temperatures. TPR shows that the decomposition of N2O into N2 over ZrO2 becomes significant only at temperatures higher than 750 K, especially after the evolution of dioxygen (the desorption of adsorbed oxygen). The mechanism of decomposition is discussed.

Maternal caffeine intake during pregnancy and risk of pregnancy loss: a categorical and dose–response meta-analysis of prospective studies

OBJECTIVE To assess the association between maternal caffeine intake and risk of pregnancy loss using a systematic review and meta-analysis. DESIGN Categorical and dose-response meta-analysis of prospective studies. SETTING Relevant articles were identified by searching MEDLINE and SCOPUS databases through 30 January 2015. Two authors independently extracted information from eligible studies. Random-effects models were used to derive the summary relative risks (RR) and corresponding 95% CI for specific categories of caffeine consumption and for a continuous association using generalized least-squares trend estimation. SUBJECTS A total of 130 456 participants and 3429 cases in fourteen included studies. RESULTS Compared with the reference category with no or very low caffeine intake, the RR (95% CI) of pregnancy loss was 1·02 (0·85, 1·24; I(2)=28·3%) for low intake (50-149 mg/d), 1·16 (0·94, 1·41; I 2=49·6%) for moderate intake (150-349 mg/d), 1·40 (1·16, 1·68; I(2)=18·6%) for high intake (350-699 mg/d) and 1·72 (1·40, 2·13; I(2)=0·0%) for very high intake (≥ 700 mg/d). In the dose-response analysis, each 100 mg/d increment in maternal caffeine intake (~1 cup of coffee) was associated with 7% (95% CI 3%, 12%) higher risk of pregnancy loss. Our results may have been affected by publication bias, but the association remained significant for the subset of larger studies. Furthermore, adjustment for smoking and pregnancy symptoms may have been incomplete, potentially resulting in residual confounding. CONCLUSIONS Albeit inconclusive, higher maternal caffeine intake was associated with a higher risk of pregnancy loss and adherence to guidelines to avoid high caffeine intake during pregnancy appears prudent.

FTIR, XPS and TPR studies of N2O decomposition over Cu‐ZSM‐5

Decomposition of N 2 O on Cu-ZSM-5 was studied by temperature-programmed reaction (TPR), in situ Fourier transform infrared spectroscopy (FTIR) and XPS. It is found that the decomposed intermediates of N 2 O-dinitrogen and oxygen ion-show absorption bands at 2161 cm -1 and 910 cm -1 in the IR spectrum, which can be assigned respectively to as N-N stretching vibration and a T-O stretching vibration perturbed by Cu 2+ . Both bands increase in intensity with temperature in the range 25-250°C. Unlike the band at 2161 cm -1 , whose intensity decreases sharply above 250°C, the band at 910 cm -1 still persists at higher temperatures. The IR results agree with the TPR profiles of N 2 and O 2 : N 2 starts to desorb at 250°C whereas O 2 remains until 310°C, where N 2 O decomposes. An oscillation in the O 2 signal is observed between 400 and 550°C, along with a more evident but opposite oscillation in the N 2 O signal. The oscillation of N 2 O decomposition and the release rates of O 2 are found to correlate with the oxidation-reduction of copper sites by XPS. Based on this evidence, Cu + is proposed to be the active centre for dissociative adsorption of N 2 O. The removal of adsorbed oxygen ions through recombination as O 2 or through interaction with protons trapped in the zeolite cavities may preserve Cu in the +1 oxidation state, which enables continuous decomposition of N 2 O.

Maternal Folate Status, but Not That of Vitamins B-12 or B-6, Is Associated with Gestational Age and Preterm Birth Risk in a Multiethnic Asian Population

BACKGROUND Maternal folate, vitamin B-12, and vitamin B-6 concentrations during pregnancy have been shown to influence birth outcomes, but the evidence is inconclusive. OBJECTIVE We aimed to examine the associations of maternal B-vitamin status with gestational age, birth weight, and length in a birth cohort study in Singapore. METHODS Maternal blood samples (n = 999) collected during weeks 26-28 of gestation were assayed for plasma folate, vitamin B-12, and vitamin B-6 concentrations. Birth weight and gestational age data were obtained from hospital records, and other anthropometric variables were measured within 72 h after birth. Relations between B-vitamin status and birth outcomes were assessed by linear or logistic regression with adjustment for potential confounders. RESULTS Median (IQR) plasma concentrations were 34.4 (24.5-44.6) nmol/L for folate, 209 (167-258) pmol/L for vitamin B-12, and 61.8 (25.9-113) nmol/L for vitamin B-6. We found that higher plasma folate concentrations were associated with a longer gestational age (0.12 wk per SD increase in folate; 95% CI: 0.02, 0.21) and tended to be associated with lower risk of all preterm birth (delivery at <37 wk of gestation; OR: 0.79; 95% CI: 0.63, 1.00) and spontaneous preterm birth (OR: 0.76; 95% CI: 0.56, 1.04). Overall, concentrations of maternal folate, vitamin B-12, and vitamin B-6 were not independently associated with birth weight or being born small for gestational age (SGA; birth weight <10th percentile for gestational age). CONCLUSIONS Higher maternal folate concentrations during late pregnancy were associated with longer gestational age and tended to be associated with a lower risk of preterm birth in this multiethnic Asian population. In contrast, the results of our study suggested little or no benefit of higher folate concentrations for reducing the risk of SGA or of higher vitamin B-6 and vitamin B-12 concentrations for reducing the risk of preterm birth or SGA.

Maternal Macronutrient Intake during Pregnancy Is Associated with Neonatal Abdominal Adiposity: The Growing Up in Singapore Towards healthy Outcomes (GUSTO) Study.

BACKGROUND Infant body composition has been associated with later metabolic disease risk, but few studies have examined the association between maternal macronutrient intake and neonatal body composition. Furthermore, most of those studies have used proxy measures of body composition that may not reflect body fat distribution, particularly abdominal internal adiposity. OBJECTIVE We investigated the relation between maternal macronutrient intake and neonatal abdominal adiposity measured by using MRI in a multiethnic Asian mother-offspring cohort. METHODS The macronutrient intake of mothers was ascertained by using a 24-h dietary recall at 26-28 wk gestation. Neonatal abdominal adiposity was assessed by using MRI in week 2 of life. Mother-offspring dyads with complete macronutrient intake and adiposity information (n = 320) were included in the analysis. Associations were assessed by both substitution and addition models with the use of multivariable linear regressions. RESULTS Mothers (mean age: 30 y) consumed (mean ± SD) 15.5% ± 4.3% of their energy from protein, 32.4% ± 7.7% from fat, and 52.1% ± 9.0% from carbohydrate. A higher-protein, lower-carbohydrate or -fat diet during pregnancy was associated with lower abdominal internal adipose tissue (IAT) in the neonates [β (95% CI): -0.18 mL (-0.35, -0.001 mL) per 1% protein-to-carbohydrate substitution and -0.25 mL (-0.46, -0.04 mL) per 1% protein-to-fat substitution]. These associations were stronger in boys than in girls (P-interaction < 0.05). Higher maternal intake of animal protein, but not plant protein, was associated with lower offspring IAT. In contrast, maternal macronutrient intake was not associated consistently with infant anthropometric measurements, including abdominal circumference and subscapular skinfold thickness. CONCLUSIONS Higher maternal protein intake at the expense of carbohydrate or fat intake at 26-28 wk gestation was associated with lower abdominal internal adiposity in neonates. Optimizing maternal dietary balance might be a new approach to improve offspring body composition. This trial was registered at clinicaltrials.gov as NCT01174875.

Infant body mass index peak and early childhood cardio-metabolic risk markers in a multi-ethnic Asian birth cohort

Background : Infant body mass index (BMI) peak has received much interest recently as a potential predictor of future obesity and metabolic risk. No studies, however, have examined infant BMI peak in Asian populations, in whom the risk of metabolic disease is higher. Methods : We utilized data among 1020 infants from a mother-offspring cohort, who were Singapore citizens or permanent residents of Chinese, Malay or Indian ethnicity with homogeneous parental ethnic backgrounds, and did not receive chemotherapy, psychotropic drugs or have diabetes mellitus. Ethnicity was self-reported at recruitment and later confirmed using genotype analysis. Subject-specific BMI curves were fitted to infant BMI data using natural cubic splines with random coefficients to account for repeated measures in each child. We estimated characteristics of the childs BMI peak [age and magnitude at peak, average pre-peak velocity (aPPV)]. Systolic (SBP) and diastolic blood pressure (DBP), BMI, sum of skinfolds (SSF) and fat-mass index (FMI) were measured during a follow-up visit at age 48 months. Weighted multivariable linear regression was used to assess the predictors (maternal BMI, gestational weight gain, ethnicity, infant sex, gestational age, birthweight-for-gestational age and breastfeeding duration) of infant BMI peak and its associations with outcomes at 48 months. Comparisons between ethnicities were tested using Bonferroni post-hoc correction. Results : Of 1020 infants, 80.5% were followed up at the 48-month visit. Mean (SD) BMI, SSF and FMI at 48 months were 15.6 (1.8) kg/m 2 , 16.5 (5.3) mm and 3.8 (1.3) kg/m 2 , respectively. Mean (SD) age at peak BMI was 6.0 (1.6) months, with a magnitude of 17.2 (1.4) kg/m 2 and pre-peak velocity of 0.7 (0.3) kg/m 2 /month. Compared with Chinese infants, the peak occurred later in Malay {B [95% confidence interval (CI): 0.64 mo (0.36, 0.92)]} and Indian infants [1.11 mo (0.76, 1.46)] and was lower in magnitude in Indian infants [-0.45 kg/m 2 (-0.69, -0.20)]. Adjusting for maternal education, BMI, gestational weight gain, ethnicity, infant sex, gestational age, birthweight-for-gestational-age and breastfeeding duration, higher peak and aPPV were associated with greater BMI, SSF and FMI at 48 months. Age at peak was positively associated with BMI at 48 months [0.15 units (0.09, 0.22)], whereas peak magnitude was associated with SBP [0.17 units (0.05, 0.30)] and DBP at 48 months [0.10 units (0.01, 0.22)]. Older age and higher magnitude at peak were associated with increased risk of overweight at 48 months [Relative Risk (95% CI): 1.35 (1.12-1.62) for age; 1.89 (1.60-2.24) for magnitude]. The associations of BMI peak with BMI and SSF at 48 months were stronger in Malay and Indian children than in Chinese children. Conclusions : Ethnic-specific differences in BMI peak characteristics, and associations of BMI peak with early childhood cardio-metabolic markers, suggest an important impact of early BMI development on later metabolic outcomes in Asian populations.

Associations of maternal macronutrient intake during pregnancy with infant BMI peak characteristics and childhood BMI

Background: Infant body mass index (BMI) peak characteristics and early childhood BMI are emerging markers of future obesity and cardiometabolic disease risk, but little is known about their maternal nutritional determinants.Objective: We investigated the associations of maternal macronutrient intake with infant BMI peak characteristics and childhood BMI in the Growing Up in Singapore Towards healthy Outcomes study.Design: With the use of infant BMI data from birth to age 18 mo, infant BMI peak characteristics [age (in months) and magnitude (BMIpeak; in kg/m2) at peak and prepeak velocities] were derived from subject-specific BMI curves that were fitted with the use of mixed-effects model with a natural cubic spline function. Associations of maternal macronutrient intake (assessed by using a 24-h recall during late gestation) with infant BMI peak characteristics (n = 910) and BMI z scores at ages 2, 3, and 4 y were examined with the use of multivariable linear regression.Results: Mean absolute maternal macronutrient intakes (percentages of energy) were 72 g protein (15.6%), 69 g fat (32.6%), and 238 g carbohydrate (51.8%). A 25-g (∼100-kcal) increase in maternal carbohydrate intake was associated with a 0.01/mo (95% CI: 0.0003, 0.01/mo) higher prepeak velocity and a 0.04 (95% CI: 0.01, 0.08) higher BMIpeak These associations were mainly driven by sugar intake, whereby a 25-g increment of maternal sugar intake was associated with a 0.02/mo (95% CI: 0.01, 0.03/mo) higher infant prepeak velocity and a 0.07 (95% CI: 0.01, 0.13) higher BMIpeak Higher maternal carbohydrate and sugar intakes were associated with a higher offspring BMI z score at ages 2-4 y. Maternal protein and fat intakes were not consistently associated with the studied outcomes.Conclusion: Higher maternal carbohydrate and sugar intakes are associated with unfavorable infancy BMI peak characteristics and higher early childhood BMI. This trial was registered at clinicaltrials.gov as NCT01174875.

Higher Maternal Dietary Protein Intake Is Associated with a Higher Risk of Gestational Diabetes Mellitus in a Multiethnic Asian Cohort

Background: Dietary protein may affect glucose metabolism through several mechanisms, but results from studies on dietary protein intake and risk of gestational diabetes mellitus (GDM) have been inconsistent.Objective: We examined the cross-sectional associations of dietary protein intake from different food sources during pregnancy with the risk of GDM in a multiethnic Asian population.Methods: We included 980 participants with singleton pregnancies from the Growing Up in Singapore Toward healthy Outcomes (GUSTO) cohort. Protein intake was ascertained from 24-h dietary recall and 3-d food diaries at 26-28 wk gestation. GDM was defined as fasting glucose ≥7.0 mmol/L and/or 2-h postload glucose ≥7.8 mmol/L at 26-28 wk gestation. We evaluated the association of dietary protein intake with GDM risk by substituting carbohydrate with protein in an isocaloric model with the use of multivariable logistic regression analysis.Results: The prevalence of GDM was 17.9% among our participants. After adjustment for potential confounders, a higher total dietary protein intake was associated with a higher risk of GDM; the OR comparing the highest with the lowest quartile of intake was 2.15 (95% CI: 1.27, 3.62; P-trend = 0.016). Higher intake levels of both animal protein (OR: 2.87; 95% CI: 1.58, 5.20; P-trend = 0.001) and vegetable protein (OR: 1.78; 95% CI: 0.99, 3.20; P-trend = 0.009) were associated with a higher risk of GDM. Among the animal protein sources, higher intake levels of seafood protein (OR: 2.17; 95% CI: 1.26, 3.72; P-trend = 0.023) and dairy protein (OR: 1.87; 95% CI: 1.11, 3.15; P-trend = 0.017) were significantly associated with a higher GDM risk.Conclusion: Higher intake levels of both animal and vegetable protein were associated with a higher risk of GDM in Asian women. This trial was registered at clinicaltrials.gov as NCT01174875.