Tunable Gas Admission via a "Molecular Trapdoor" Mechanism in a Flexible Cationic Metal-Organic Framework Featuring 1D Channels

Achieving high gas selectivity is challenging when dealing with gas pairs of similar size and physiochemical properties. The "molecular trapdoor" mechanism discovered in zeolites holds promise for highly selective gas adsorption separation but faces limitations like constrained pore volume and slow adsorption kinetics. To address these challenges, for the first time, a flexible metal-organic framework (MOF) featuring 1D channels and functioning as a "molecular trapdoor" material is intoduced. Extra-framework anions act as "gate-keeping" groups at the narrowest points of channels, permitting gas admissions via gate opening induced by thermal/pressure stimuli and guest interactions. Different guest molecules induce varied energy barriers for anion movement, enabling gas separation based on distinct threshold temperatures for gas admission. The flexible framework of Pytpy MOFs, featuring swelling structure with rotatable pyridine rings, facilitates faster gas adsorption than zeolite. Analyzing anion properties of Pytpy MOFs reveals a guiding principle for selecting anions to tailor threshold gas admission. This study not only overcomes the kinetic limitations related to gas admission in the "molecular trapdoor" zeolites but also underscores the potential of developing MOFs as molecular trapdoor adsorbents, providing valuable insights for designing ionic MOFs tailored to diverse gas separation applications.

2D Semi-Metallic Hafnium Ditelluride: A Novel Nonlinear Optical Material for Ultrafast and Ultranarrow Photonics Applications

2D semi-metallic hafnium ditelluride material is used in several applications such as solar steam generation, gas sensing, and catalysis owing to its strong near-infrared absorbance, high sensitivity, and distinctive electronic structure. The zero-bandgap characteristics, along with the thermal and dynamic stability of 2D-HfTe2, make it a desirable choice for developing long-wavelength-range photonics devices. Herein, the HfTe2 -nanosheets are prepared using the liquid-phase exfoliation method, and their superior nonlinear optical properties are demonstrated by the obtained modulation depth of 11.9% (800 nm) and 6.35% (1560 nm), respectively. In addition, the observed transition from saturable to reverse saturable absorption indicates adaptability of the prepared material in nonlinear optics. By utilizing a side polished fiber-based HfTe2 -saturable absorber (SA) inside an Er-doped fiber laser cavity, a mode-locked laser with 724 fs pulse width and 56.63 dB signal-to-noise ratio (SNR) is realized for the first time. The generated laser with this SA has the second lowest mode-locking pump threshold (18.35 mW), among the other 2D material based-SAs, thus paving the way for future laser development with improved efficiency and reduced thermal impact. Finally, employing this HfTe2 -SA, a highly stable single-frequency fiber laser (SNR ≈ 74.56 dB; linewidth ≈ 1.268 kHz) is generated for the first time, indicating its promising ultranarrow photonic application.

[Meta-analysis of the correlation between prenatal steroid exposure and hypoglycemia in late preterm neonates]

Objective: To systematically evaluate the correlation between prenatal steroid exposure and hypoglycemia in late preterm neonates. Methods: Eight databases in either Chinese or English, including PubMed, the Cochrane Library, Embase, Medline, Scopus, CNKI, Wanfang and VIP, were searched to extract the studies on the correlation between prenatal steroid exposure and hypoglycemia in late preterm neonates published from the establishment of each database to December 2022. The Meta-analysis was performed using Stata 14.0 statistical software. Results: A total of 9 studies were included in this Meta-analysis, including 6 retrospective cohort studies, 2 prospective cohort studies and 1 randomized controlled trial (RCT) study, involving 9 143 premature infants. The Meta-analysis showed that prenatal steroid exposure increased the risk of late preterm neonatal hypoglycemia (RR=1.55, 95%CI 1.25-1.91, P<0.001). The similar correlation between prenatal steroid exposure and hypoglycemia in late preterm neonates was all found in the following subgroups: North America (RR=1.57, 95%CI 1.37-1.80, P<0.001), enrolling pregnant women with gestational diabetes (RR=1.62, 95%CI 1.26-2.08, P<0.001), A-grade literature quality (RR=1.43, 95%CI 1.14-1.79, P=0.002), criteria for hypoglycemia ≤40 mg/dl (1 mg/dl=0.056 mmol/L, RR=1.49, 95%CI 1.28-1.73, P<0.001), sample size of 501-1 500 (RR=1.69, 95%CI 1.19-2.40, P=0.003) and >1 500 (RR=1.65, 95%CI 1.48-1.83, P<0.001), steroid injection dosage and frequency of 12 mg 2 times (RR=1.66, 95%CI 1.50-1.84, P<0.001), the time interval from antenatal corticosteroid administration to delivery of 24-47 h (RR=1.98, 95%CI 1.26-3.10, P=0.003), unadjusted gestational age (RR=1.78, 95%CI 1.02-3.10,P=0.043) and unadjusted birth weight (RR=1.80, 95%CI 1.22-2.66, P=0.003). Meta-regression results showed that steroid injection frequency and dose were the main sources of high heterogeneity among studies (P=0.030). Conclusion: Prenatal steroid exposure may be a risk factor for hypoglycemia in late preterm neonates.

Influence of Defect Number, Distribution Continuity and Orientation on Tensile Strengths of the CNT-Based Networks: A Molecular Dynamics Study

Networks based on carbon nanotube (CNT) have been widely utilized to fabricate flexible electronic devices, but defects inevitably exist in these structures. In this study, we investigate the influence of the CNT-unit defects on the mechanical properties of a honeycomb CNT-based network, super carbon nanotube (SCNT), through molecular dynamics simulations. Results show that tensile strengths of the defective SCNTs are affected by the defect number, distribution continuity and orientation. Single-defect brings 0 ~ 25% reduction of the tensile strength with the dependency on defect position and the reduction is over 50% when the defect number increases to three. The distribution continuity induces up to 20% differences of tensile strengths for SCNTs with the same defect number. A smaller arranging angle of defects to the tensile direction leads to a higher tensile strength. Defective SCNTs possess various modes of stress concentration with different concentration degrees under the combined effect of defect number, arranging direction and continuity, for which the underlying mechanism can be explained by the effective crack length of the fracture mechanics. Fundamentally, the force transmission mode of the SCNT controls the influence of defects and the cases that breaking more force transmission paths cause larger decreases of tensile strengths. Defects are non-negligible factors of the mechanical properties of CNT-based networks and understanding the influence of defects on CNT-based networks is valuable to achieve the proper design of CNT-based electronic devices with better performances.