Synthesis and Properties of Nitrogen-Doped Carbon Quantum Dots Using Lactic Acid as Carbon Source

Nitrogen-doped carbon quantum dots (N-CQDs) were synthesized in a one-step hydrothermal technique utilizing L-lactic acid as that of the source of carbon and ethylenediamine as that of the source of nitrogen, and were characterized using dynamic light scattering, X-ray photoelectron spectroscopy ultraviolet-visible spectrum, Fourier-transformed infrared spectrum, high-resolution transmission electron microscopy, and fluorescence spectrum. The generated N-CQDs have a spherical structure and overall diameters ranging from 1–4 nm, and their surface comprises specific functional groups such as amino, carboxyl, and hydroxyl, resulting in greater water solubility and fluorescence. The quantum yield of N-CQDs (being 46%) is significantly higher than that of the CQDs synthesized from other biomass in literatures. Its fluorescence intensity is dependent on the excitation wavelength, and N-CQDs release blue light at 365 nm under ultraviolet light. The pH values may impact the protonation of N-CQDs surface functional groups and lead to significant fluorescence quenching of N-CQDs. Therefore, the fluorescence intensity of N-CQDs is the highest at pH 7.0, but it decreases with pH as pH values being either more than or less than pH 7.0. The N-CQDs exhibit high sensitivity to Fe3+ ions, for Fe3+ ions would decrease the fluorescence intensity of N-CQDs by 99.6%, and the influence of Fe3+ ions on N-CQDs fluorescence quenching is slightly affected by other metal ions. Moreover, the fluorescence quenching efficiency of Fe3+ ions displays an obvious linear relationship to Fe3+ concentrations in a wide range of concentrations (up to 200 µM) and with a detection limit of 1.89 µM. Therefore, the generated N-CQDs may be utilized as a robust fluorescence sensor for detecting pH and Fe3+ ions

The COVID-19 Vaccination and Vaccine Inequity Worldwide: An Empirical Study Based on Global Data

Vaccination is critical for controlling the COVID-19 pandemic. However, the progress of COVID-19 vaccination varies from different countries, and global vaccine inequity has been a worldwide public health issue. This study collected data from the Our World in Data COVID-19 vaccination data set between 13 December 2020 and 1 January 2022. The measurement reflecting the pandemic situation included New cases, New deaths, Hospital patients, ICU patients, and the Reproduction rate. Indicators for measuring the vaccination coverage included Total vaccinations per hundred and People vaccinated per hundred. The Human Development Index (HDI) measured the country’s development level. Findings indicated that countries with higher HDI have more adequate vaccine resources, and global vaccine inequity exists. The study also found that vaccination significantly mitigates the pandemic, and reaching 70% immunization coverage can further control the epidemic. In addition, the emergence of Omicron variants makes the COVID-19 epidemic situation even worse, suggesting the importance and necessity of addressing vaccine inequity. The globe will face a greater challenge in controlling the pandemic if lower-vaccinated countries do not increase their vaccination coverage. Addressing the issue of vaccine inequity needs the cooperation of HIC, LMIC, public health departments, and vaccine producers. Moreover, the media has to contribute to effective public health communication by raising public perceptions of the COVID-19 pandemic, vaccination, and vaccine inequity

Preparation and Properties of Stereocomplex of Poly(lactic acid) and Its Amphiphilic Copolymers Containing Glucose Groups

The stereocomplex of poly(lactic acid) containing glucose groups (sc-PLAG) was prepared by solution blending from equal amounts of poly(l-lactic acid) (PLLA) and poly(d-lactic acid-co-glucose) (PDLAG), which were synthesized from l- and d-lactic acid and glucose by melt polycondensation. The methods, including 1H nuclear magnetic resonance spectroscopy (1H NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), polarizing microscope (POM), scanning electron microscope (SEM), transmission electron microscope (TEM), and contact angle were used to determine the effects of the stereocomplexation of enantiomeric poly(lactic acid) (PLA) units, the amphiphilicity due to glucose residues and lactic acid units, and the interaction of glucose residues with lactic units on the crystallization performance, hydrophilicity, thermal stability, and morphology of samples. The results showed PDLAG was multi-armed, and partial OH groups of glucose residues in PDLAG might remain unreacted. The molecular weight (Mw), dispersity (Ɖ), and glucose proportion in the chain of PDLAG thereby had significant effects on sc-PLAG. There were the stereocomplexation of enantiomeric lactic units and the amphiphilic self-assembly of PDLAG in sc-PLAG, which resulted in glucose groups mainly in the surface phase and lactic units in the bulk phase. The sc-PLAG only possessed the stereocomplex crystal owing to the interaction between nearly equimolar of l-lactic units of PLLA and d-lactic units of PDLAG, and had no homo-crystallites of l- or d-lactic units, which improved the melting temperature (Tm) of sc-PLAG about 50 °C higher than that of PLLA. Glucose groups in sc-PLAG played an important role by forming heterogeneous nucleation, promoting amphiphilic self-assembly, and affecting the ordered arrangement of lactic units. The glass transition temperature (Tg), the melting temperature (Tm), crystallinity, crystallization rate, and water absorption of sc-PLAG showed similar changes with the increased glucose content in feeding. All these parameters increased at first, and the maximum appeared as glucose content in feeding about 2%, such as the maximum crystallinity of 48.8% and the maximum water absorption ratio being 11.7%. When glucose content in feeding continued increasing, all these performances showed a downward trend due to the decrease of arrangement regularity of lactic acid chains caused by glucose groups. Moreover, the contact angle of sc-PLAG decreased gradually with the increased glucose content in feeding to obtain the minimum 77.5° as the glucose content in feeding being 5%, while that of PLLA was 85.0°. The sc-PLAG possessed a regular microsphere structure, and its microspheres with a diameter of about 200 nm could be observed. In conclusion, sc-PLAG containing proper glucose amount could effectively enhance the crystallinity, hydrophilicity, and thermal stability of PLA material, which is useful for drug delivery, a scaffold for tissue engineering, and other applications of biomedicine

Role of the Branched PEG‑<i>b</i>‑PLLA Block Chain in Stereocomplex Crystallization and Crystallization Kinetics for PDLA/MPEG‑<i>b</i>‑PLLA‑<i>g</i>‑glucose Blends with Different Architectures

The isothermal crystallization behavior and corresponding morphology evolution of poly(d-lactic acid) (PDLA) blends with PLLA6.7k or MPEG-b-PLLA6.7k-g-glucose with different architectures and different PLLA-grafted copolymer contents were investigated. The formation of stereocomplexes (SCs) in between the chain branched structure of MPEG-b-PLLA6.7k-g-glucose and PDLA chains acting as the physical crosslinking points slows down the motion of PDLA chains, but the SCs could act as a heterogeneous nucleating agent for the late formation of homocrystals (HCs) in the blend system, accelerating the crystallization kinetics of HCs through enhancing the nucleation density. For PDLA/MPEG-b-PLLA6.7k-g-glucose blends, the mobility of SCs in the blend system and the nucleation density of SCs in the blends exhibit oppositional behavior during the isothermal crystallization at a Tc of 130 °C. The evolution of the crystal growth and structure during the isothermal crystallization process by rheometry has revealed the interesting role of the branched chains of MPEG-b-PLLA6.7k-g-glucose in the mechanism of the crystallization in PDLA blends

Design of Heterogeneous Nuclei Composed of Uniaxial Cellulose Nanocrystal Assemblies for Epitaxial Growth of Poly(ε-caprolactone)

Epitaxial crystallization is the most prominent approach to achieving oriented thin films composed of semicrystalline polymers (SCPs). Nevertheless, current templates remain limited in fulfilling oriented SCPs with high-throughput coating processes. Herein, we report the first template for the epitaxial crystallization of SCPs based on a uniaxial assembly of shape-anisotropic nanocrystalscellulose nanocrystals (CNCs). The template was fabricated via a dip-coating method, leading to a uniaxial thin coating on both planar and nonplanar substrates. Such a thin coating functioned similarly to a laterally oriented SCP thin film in regulating the crystallization behaviors of poly­(ε-caprolactone) (PCL). The orientational relationship between the CNC thin coating and the PCL overlayer was studied systematically by employing multiple characterization tools including scattering, diffraction, and microscopy. Moreover, the epitaxial match based on the crystallography-regulated hydrogen-bonding networks between the two layers was confirmed by molecular modeling, in agreement with the experimental results. Besides the orientational regulation, CNCs also promoted the crystallization kinetics of PCL effectively due to the nanoepitaxial effect provided by each CNC particle. We highlight this facile assembly approach to heterogeneous nuclei for the epitaxial crystallization of SCPs and its extendability of achieving thin coatings composed of 3D-oriented SCPs on ambient substrates

Design of Heterogeneous Nuclei for Lateral Crystallization via Uniaxial Assembly of Cellulose Nanocrystals

Semicrystalline polymers (SCPs) represent a group of cheap heterogeneous nuclei for crystallization. Nevertheless, cellulose, the most abundant biogenic SCP, is notorious for its poor processability. This limits its application as the orientational guiding agent in crystallization of functional compounds. Different from current polymer engineering approaches to uniaxial SCP thin films, we explored a novel approach to the uniaxial cellulose thin film via the oriented assembly of cellulose nanocrystals (CNCs) by means of a simple dip-coating technique. This thin film successfully guides the lateral crystallization of two drug compounds, which in turn reflects the uniformity of the uniaxial CNC alignment on the macroscopic scale. Furthermore, unlike traditional SCP thin films, the assembly route driven by different external forces can lead to CNC thin films with distinct orientational characters for fabrication of patterned drug thin films. The emerging colloidal assembly route to a uniaxial SCP substrate leads to unprecedented access to design heterogeneous nuclei for oriented crystallization of functional hybrids

Effects of flora deficiency on the structure and function of the large intestine

Summary: The significant anatomical changes in large intestine of germ-free (GF) mice provide excellent material for understanding microbe-host crosstalk. We observed significant differences of GF mice in anatomical and physiological involving in enlarged cecum, thinned mucosal layer and enriched water in cecal content. Furthermore, integration analysis of multi-omics data revealed the associations between the structure of large intestinal mesenchymal cells and the thinning of the mucosal layer. Increased Aqp8 expression in GF mice may contribute to enhanced water secretion or altered hydrodynamics in the cecum. In addition, the proportion of epithelial cells, nutrient absorption capacity, immune function and the metabolome of cecum contents of large intestine were also significantly altered. Together, this is the first systematic study of the transcriptome and metabolome of the cecum and colon of GF mice, and these findings contribute to our understanding of the intricate interactions between microbes and the large intestine